Check your radiator/condenser fan operation NOW

[DanG144]

Continuously high as far as I can tell, any time the key is turned on or the engine is running. They switch off as soon as the key is removed, even if the engine is hot.

I have had several people tell me the fans were in fast, when indeed they were in slow. You can either do the fan tests in the first post to calibrate your ear, or listen to a similar car. But assuming you can tell...

Is this even with the AC selected to OFF (on a car parked overnight)? If so...

Unplug the HP sensor, see what happens. If the fans stop, then that is the culprit. (I was wondering if your HP sensor readings were inverted. I have run into meters before that read 80% when in actuality it was 20%. If this is happening to you then you are reading very high -more than high enough to cause the fans to run in fast, almost high enough to trip off the compressor.) You can find info in the Pdfs in the first post on expected readings vs ambient temperature on a check done after being parked 8 hours. 20% is very low for the summertime.

If unplugging the HP sensor does not stop the fans, then unplug the radiator thermoswitch, see if they stop. If so, then this is the culprit. If they still run fast, and it was not the HP sensor, then it is a bad FCM. (If the ECU was asking for fast fans due to a high Coolant Temperature Sensor Signal, I think it also turns off the
AC clutch. You can check with VCDS.

 

[ymz]

...If it is stiff, it is probably not worth replacing the coil ...

Well, as I was loosening the nut at the front of the compressor, the shaft broke around 1/4" past the nut...

This car's not worth putting in a replacement compressor, so I guess I'll just remove the clutch disc to avoid having it pop off (perhaps cement it in place with Loctite Red ??) and run without a/c... (unless I can find a place that rents a refrigerant recovery unit - not likely around here...)

Thanks (yet again!!) for your help...

Yuri

 

[djdad]

No low speed on either fan

Hey, Dan--you are pretty popular!

2002 Jetta w/ALH engine.

Just had my car to the shop because A/C was not running as cold as it should. They found that it needed a recharge, which they did along with adding some dye to be able to check for leaks. They also told me that the driver's side fan is shot. I told them that I would take care of the fan.

I got home and looked in Bentley. I checked the fuses and links, and they are OK. I shorted across the thermoswitch connector terminals and found that neither slow nor fast speeds work with the ignition off and only fast works with the ignition on--both fans.

I then found your post. It is EXTREMELY helpful! Both fans run fast with ignition and A/C switches on. When tested directly (your favorite method), both fans run both slow and fast. Pin 2 of the thermoswitch connector has battery voltage. With the thermoswitch pins 1 & 2 jumped, my test light (which I verified works correctly) did not light when put across pins 2 & 3 of either fan wiring harness connector. Per your write-up, there is a fault somewhere in the wiring, not a bad FCM. Does that mean not necessarily a bad FCM or definitely not a bad FCM? And since the problem lies in the wiring somewhere, is there a progression from most likely place to look to least likely place to look?

Thank you!

 

[DanG144]

If the fans work in slow with direct feed, and not from the slow speed contacts for the Radiator thermoswitch feed, it can be a combination of the voltage drops in the connections in the power flow path not being present which can provide more EMF to overcome poor contacts in the fan (normally brushes being held in position by melted holders or dirt), or it can simply be a broken wire.

As you can see from schematic 38 in your Bentley manual, when you are trying to power the fans from the thermoswitch the FCM is not even in the equation, hence my statement at this point in the discussion. There is no guarantee, however that the FCM is GOOD, just that it is not causing the fans not to run from the thermoswitch.

If you want to know for sure, take voltage readings at the fan connector while trying to run both fans (so you have full load, dropping more voltage than a single fan would) from the thermoswitch and from the FCM. Then look at the voltage at the fan contact when powering it directly from a battery with a large (10 gauge) wire.

If degraded voltage is present from the normal flow paths, then you can start measuring voltages at different points in the path (while under load) to find the culprit. Quite often just plugging and unplugging fuses and connectors can wipe the corrosion off enough that the fan might get enough voltage to turn.

In my own case, I put in a large (40 amp) circuit breaker to replace one of my fuses on top the battery that had developed a bad connection. I just took power from the hot side of one of the strip fuses to feed it. Those fuse panels above the battery are so poor, and so expensive, that i will do this instead of replacing it in kind, as my car ages.

 

[DanG144]

There is a splice connection, K21 in the positive side of the fan wiring, below the battery, best found by starting at the fan connector and peeling back the cover as you work toward the battery and thermoswitch. One person found the wires corroded through near this junction recently.

There is also a splice 193 in the ground wiring from the fans, same story, work your way up to the ground points under the battery.

While you are there, take the grounds up, polish them and clean them, then put them back down. Examine the crimps for corrosion. You can end up with a high resistance contact from the wire to lug crimp, even if everything else is fine. This is most easily found by loading the circuit and feeling for hot spots. Any hot spot is a problem.

Good job with the troubleshooting, and the questions.

 

[DanG144]

General notice.

Over the 10 years I have been helping folks wth VW AC systems (7.5 years in this thread), I have had several people say they will draw up some schematics to post here. No one has ever done it, though.

It is easy enough to talk intelligently with owners of Bentley Manuals (especially the ones that actually use them), but it is extremely frustrating to work with the others on circuit issues.

My own efforts have proven illegible.

If anyone can help out the community with this, it would be most welcome.

 

[ngng]

ngng,
I suspect that AnotherPerson is talking about the CTS, coolant temperature sensors, just off the head, not the AC high temperature cutout switch that we are referring to in your early model MKIV.

So you have confirmed that it is the early model, and thus you troubleshoot it with the "Sept 98 - May 99 Build date A4 Manual Air Conditioner Troubleshooting "

My earlier statement was trying to point out that the guide (also a PDF linked in the first post of this thread) for the cars built a month after yours is much more detailed and thorough - simply because I could use my car as a guinea pig and test things out.

If you have not located and tested the F38 low temperature cutout switch (and it is an actual switch for your car, not a thermistor as on later cars) then that is where I would start.

Owners of cars built after April of 99, stop reading, don't jumper anything or you will cause damage.
Since yours is an actual switch, you can simply jumper around it for testing, once you find it. Or You can simply jumper from pin 2 of the F163 high temperature cutout switch to pin 2 of the four wire connector for your AC pressure switch. If your AC starts working when you do this, then it is the wiring, ambient temp switch, or high temp cutout switch. If this does not work, then verify that you are getting 12v at pin 2 of the pressure switch.

Be sure to refer to schematic 14, starting on page 97-152 of your Bentley manual.

Good job troubleshooting so far,

I've removed the ambient temp switch and have ordered a new Meyle replacement (PN 1H0959625 for future reference). On my 4/99 it required removing both wipers to access; it was on the far left side of the car. I tried jumping the harness but that didn't seem to do anything. I wasn't quite sure how to test the sensor itself (but it looked old, and when I shook it sounded like something was broken inside).

Where can I find the pinouts for the F163 and AC pressure switch? I don't see these in the Bentley.

Regarding the temp cut out switch, this is the Delphi replacement that I purchased. It appears to be blue? Not sure if it should be green. I will try jumping this connector when the new ambient temp switch arrives.

http://www.ebay.com/itm/272315215775

[img 500x500]http://i.imgur.com/EFyVUh7.jpg[/img]

Thanks!

 

[ngng]

ngng,
I suspect that AnotherPerson is talking about the CTS, coolant temperature sensors, just off the head, not the AC high temperature cutout switch that we are referring to in your early model MKIV.

So you have confirmed that it is the early model, and thus you troubleshoot it with the "Sept 98 - May 99 Build date A4 Manual Air Conditioner Troubleshooting "

My earlier statement was trying to point out that the guide (also a PDF linked in the first post of this thread) for the cars built a month after yours is much more detailed and thorough - simply because I could use my car as a guinea pig and test things out.

If you have not located and tested the F38 low temperature cutout switch (and it is an actual switch for your car, not a thermistor as on later cars) then that is where I would start.

Owners of cars built after April of 99, stop reading, don't jumper anything or you will cause damage.
Since yours is an actual switch, you can simply jumper around it for testing, once you find it. Or You can simply jumper from pin 2 of the F163 high temperature cutout switch to pin 2 of the four wire connector for your AC pressure switch. If your AC starts working when you do this, then it is the wiring, ambient temp switch, or high temp cutout switch. If this does not work, then verify that you are getting 12v at pin 2 of the pressure switch.

Be sure to refer to schematic 14, starting on page 97-152 of your Bentley manual.

Good job troubleshooting so far,

I've removed the ambient temp switch and have ordered a new Meyle replacement (PN 1H0959625 for future reference). On my 4/99 it required removing both wipers to access; it was on the far left side of the car. I tried jumping the harness but that didn't seem to do anything. I wasn't quite sure how to test the sensor itself (but it looked old, and when I shook it sounded like something was broken inside).

Where can I find the pinouts for the F163 and AC pressure switch? I don't see these in the Bentley.

Regarding the temp cut out switch, this is the Delphi replacement that I purchased. It appears to be blue? Not sure if it should be green. I will try jumping this connector when the new ambient temp switch arrives.

http://www.ebay.com/itm/272315215775

Thanks!

 

[DanG144]

Please do all of us a favor and remove or downsize that huge photograph. You can leave the link. That is making the thread very hard to read.

 

[DanG144]

Everyone I have ever picked up seemed to rattle when shaken. Even if it worked.

Can you confirm to me what schematic or page numbers you are looking at? Schematic number is best, as page numbers can change from edition to edition.

In my manual the schematic is #14 which has sections 1-5 on pages 97-152 to 97-156.

The F163 A/C cutout thermal switch and F38 ambient temperature switch are shown on 14/3 page 97-154. Their pin numbers, and wire colors are shown. So is the F129 4 wire pressure switch.

As I mentioned before, I have never had one of these to examine closely,

 

[DanG144]

Check the resistance pin to pin for the F38 ambient temperature switch. It should have continuity above 35 degrees F. The newer style has a thermistor in it, and should have low resistance at high temperatures, about 1k ohm at 75 degrees, perhaps. If you search on CTS and thermistor on this site, you can probably find the curve for the new style, but I was under the impression that yours was a simple switch, not a thermistor.

From the pdf in post #1 for the 98-99 cars.
"2) Check for 12 volts at the T10a connector pin No. 8 and 5 (T10b/8, T10b/5). This 12-volt signal comes from the A/C switch and requests both cooling fans on at low speed and compressor activation by the Fan Control Module. (Through fuse 25, the fresh air blower switch, the AC switch, F129 pressure switch , F38 ambient temperature switch, and F163 A/C high temperature cutout switch. This signal is also sent to the ECM, Engine Control Module.) If this voltage is not present, drop down to section B."

 

[djdad]

If the fans work in slow with direct feed, and not from the slow speed contacts for the Radiator thermoswitch feed, it can be a combination of the voltage drops in the connections in the power flow path not being present which can provide more EMF to overcome poor contacts in the fan (normally brushes being held in position by melted holders or dirt), or it can simply be a broken wire.

As you can see from schematic 38 in your Bentley manual, when you are trying to power the fans from the thermoswitch the FCM is not even in the equation, hence my statement at this point in the discussion. There is no guarantee, however that the FCM is GOOD, just that it is not causing the fans not to run from the thermoswitch.

If you want to know for sure, take voltage readings at the fan connector while trying to run both fans (so you have full load, dropping more voltage than a single fan would) from the thermoswitch and from the FCM. Then look at the voltage at the fan contact when powering it directly from a battery with a large (10 gauge) wire.

If degraded voltage is present from the normal flow paths, then you can start measuring voltages at different points in the path (while under load) to find the culprit. Quite often just plugging and unplugging fuses and connectors can wipe the corrosion off enough that the fan might get enough voltage to turn.

In my own case, I put in a large (40 amp) circuit breaker to replace one of my fuses on top the battery that had developed a bad connection. I just took power from the hot side of one of the strip fuses to feed it. Those fuse panels above the battery are so poor, and so expensive, that i will do this instead of replacing it in kind, as my car ages.

There is a splice connection, K21 in the positive side of the fan wiring, below the battery, best found by starting at the fan connector and peeling back the cover as you work toward the battery and thermoswitch. One person found the wires corroded through near this junction recently.

There is also a splice 193 in the ground wiring from the fans, same story, work your way up to the ground points under the battery.

While you are there, take the grounds up, polish them and clean them, then put them back down. Examine the crimps for corrosion. You can end up with a high resistance contact from the wire to lug crimp, even if everything else is fine. This is most easily found by loading the circuit and feeling for hot spots. Any hot spot is a problem.

Good job with the troubleshooting, and the questions.

Thank you for your replies, Dan! And thank you for your kind words. Conciseness is a trait of engineers. Unfortunately, I am a mechanical rather than an electrical engineer, so I am challenged.

I found ground connection 21 underneath the the battery support tray (outboard connection of the three that are there), disassembled, cleaned with emory cloth (even though the ring terminals were quite clean already), and reassembled using dielectric grease. I found ground circuit splice 193, which is assembled with a sealer material inside heat shrink tubing--it is clean and stable. I measured the resistance between pin 3 on each wiring harness connector for the fans and body, and both were 0.3 ohm. I found the feed circuit splice K21, which also has sealer inside heat shrink tubing, and it is clean and stable. I measured resistance between pin 1 of the thermoswitch connector and pin 2 of each of the wiring harness connectors for the fans, and both were 0.3 ohm. I noted that splice K21 includes a wire that is connected to the FCM. I disconnected the 14-pin connector from the FCM and it made no difference at all when going through the checks.

At that point, I was very perplexed. There is continuity in each circuit when no power is present, but no slow speed fan operation when power is applied. Even though both fans operate at both speeds when powered directly, I decided to check resistances per your fan testing write-up. The passenger-side fan measured close to your figures--0.8, 1.4 and 1.9 ohms, respectively. The driver-side fan measured about 3 Mohm, about 9 Mohm and 1.0 ohm, respectively. So, even though it runs, the driver-side fan is bad. But the circuit that is bad is the high-speed side. The slow speed, between pins 2 & 3 measures OK. I am even more perplexed that I was before. What is going on?

At this point, I believe that I will purchase a new driver-side fan, put my car back together, replace the fan when the new one arrives, and see how everything works at that time. If there are still operational issues, I would continue investigating. Any thoughts or alternate ideas?

Thank you!

 

[DanG144]

I would suggest trying to measure the voltage supplied to the fan side connector lugs while both fans are trying to run, so the circuit is loaded. This may show that voltage drops considerably when the circuit is loaded.

If the brushes in the fans are not being forced onto the commutator, the resistance can vary considerably. Sometimes vibration from the running engine will get you momentary contact.

 

[djdad]

I would suggest trying to measure the voltage supplied to the fan side connector lugs while both fans are trying to run, so the circuit is loaded. This may show that voltage drops considerably when the circuit is loaded.

If the brushes in the fans are not being forced onto the commutator, the resistance can vary considerably. Sometimes vibration from the running engine will get you momentary contact.

After having mixed results measuring voltages, the passenger-side fan came on! It happened when I was fiddling around with it's connector. So I fiddled around with that connector some more, but it was come-and-go. Then, I happened to bump the thermoswitch connector harness (pins 1 & 2 still being jumpered) and the passenger fan went on-off. So I grabbed the connector and tried flexing the wire bundle going into it, and the fan would turn on and off. So, since pin 2 (input) has battery voltage, the wire attached to terminal 1 (output) has a problem. That would make sense and explain what I have been experiencing. After finding that issue, I went back and checked voltages at the fan connectors. With the thermoswitch connector jumpered and the passenger-side fan running, there was about 11V at pin 2 (low speed) and about 9V at pin 1 (high speed) at both connectors. The driver-side fan was still not running.

I disconnected the battery and the driver-side fan connector. I had my meter attached to the fan terminals and set to read resistance. I spun the fan and tapped on the fan body with a small plastic mallet. Both 1-3 and 2-3 connections returned resistance values between about 1 kohm and open circuit, and fluctuating wildly. The fan is bad. My new Metrix fan is on order and will be in tomorrow morning. In the meantime, I have a wire to fix and a bunch of reassembly to do.

Thanks for your help, Dan!

Update: The pin 2 terminal in the thermoswitch connector is separated at the neck-down between the crimp and the spade. I have not been able to get the spade end out of the connector (and the lock is out). Ideas for repairing the terminal inside the connector? If there were a conductive epoxy cement available to me, I would try smearing some on both pieces and then jam the wire back in. What works?

Update 2: Got the piece of the terminal out a couple of hours ago. Now looking for a used wire with terminal piece that I can splice in.

 

[DanG144]

You have the tool, or have made one to unhook the catches, now that the lock is out?

You have to put two thin shims, one on each side of the spade, then push the spade IN further, then pull it out.

https://www.youtube.com/watch?v=5rlXZUvhEsQ

 

[ngng]

Check the resistance pin to pin for the F38 ambient temperature switch. It should have continuity above 35 degrees F. The newer style has a thermistor in it, and should have low resistance at high temperatures, about 1k ohm at 75 degrees, perhaps. If you search on CTS and thermistor on this site, you can probably find the curve for the new style, but I was under the impression that yours was a simple switch, not a thermistor.

From the pdf in post #1 for the 98-99 cars.
"2) Check for 12 volts at the T10a connector pin No. 8 and 5 (T10b/8, T10b/5). This 12-volt signal comes from the A/C switch and requests both cooling fans on at low speed and compressor activation by the Fan Control Module. (Through fuse 25, the fresh air blower switch, the AC switch, F129 pressure switch , F38 ambient temperature switch, and F163 A/C high temperature cutout switch. This signal is also sent to the ECM, Engine Control Module.) If this voltage is not present, drop down to section B."

Replaced the ambient temp sensor today and nothing comes on still. Will be testing more soon...

 

[commanderjjones]

Thanks to the info' here (especially Dan), I diagnosed my problem was the pressure switch. I replaced it and it has been working great for over a month......until last night.

NEW PROBLEM. I thought it would be a great idea to replace my interior lights with LED's (kicking myself in the butt now). In that process, I blew a fuse while prying out one of the bulbs with a screw driver. I thought, no big deal......replaced the fuse and the interior lights and power windows started working again. I didn't drive the car immediately after the light swap, but got up the next morning to go to work and noticed the A/C wasn't working very well.......then on the way home (when it was hot outside), it was BARELY working. The compressor would kick on, but only work for a few seconds and then would shut off. After a few minutes, the process repeats itself. After looking into it, I notice my fans are working on low, but not on high.

I'm fairly certain this is related to blowing that fuse. The A/C has worked flawlessly for a month.....right up until I blew that fuse during the light installation. So I checked all of the other fuses (that I could find) and they seem to be okay. What else could I have burnt when I blew that fuse? I'm hoping I didn't fry the fan control module or something. Are there other fuses or relays that would cause the fans to not work on high?

 

[DanG144]

The behavior you describe is often associated with a bad HP sensor (or switch if before May 99). Did yours have 4 wires or 3 wires?

It can also be due to high pressure if the high speed fans are indeed not working.
Try running the AC stationary at 1800 rpm, if you get the same behavior spray the condenser coil with water continuously, see if the AC stays on. If it does, then it is likely your lack of high speed fans that are the problem.

Fan issues are generally due to power delivery issues, fuses, bad connections, bad wires. The FCM can be at fault, but less likely.

Have you checked all the fuses listed in the PDF in post 1, for your car?

 

[commanderjjones]

My sensor is a 3 wire. I replaced the sensor AND the connector plug last month. I replaced the connector first because I thought that was the issue, since the A/C would kick on when I wiggled the connector. But it turned out the bad connection was on the sensor side and not in the plug end.

I missed the part about those fuses in the PDF. I'll check those and try the water test, then report back.

Thanks for pointing me in the right direction!

 

[commanderjjones]

Well, the fuses are good. Turns out that I had indeed checked those. I just wasn't sure about the description in the PDF.

Unfortunately the mosquitoes were HORRENDOUS tonight, so I didn't do the water test. I'll try that in the morning when it's cooler.

 

[commanderjjones]

The water test didn't seem to make it function any better. So I started watching closely and it appears that the compressor clutch may be slipping. I could hear it click and attempt to engage, then it would spin for a second and then start to chatter like it is slipping. The longer it ran and the hotter it got, the less the clutch worked.

Before it got hot, the compressor would run for about 3 seconds and then shut off for about 3 seconds. Is this normal? I thought that it should probably run longer before cycling off.

With the engine running, I really can't hear the fan well enough to be 100% if the fan is working on high or not. Is there a way to test fan function between low and high?

 

[SilverGhost]

First, the compressor does not cycle. Once the clutch is engaged the compressor regulates internally.

Second, normal speed is generally not too noticeable over back ground noise, but high speed sounds like a jet is starting to taxi. NOTE: both fans always turn the same speed.

If the clutch is slipping then first thing I would check is if the nut is loose. Unless someone has taken it apart then it may also have snap rings or missing/broken shims.

Jason

 

[AnotherPerson]

First, the compressor does not cycle. Once the clutch is engaged the compressor regulates internally.

Second, normal speed is generally not too noticeable over back ground noise, but high speed sounds like a jet is starting to taxi. NOTE: both fans always turn the same speed.

If the clutch is slipping then first thing I would check is if the nut is loose. Unless someone has taken it apart then it may also have snap rings or missing/broken shims.

Jason

Based on the compressor does not cycle. In my car if I rev the car when I'm stopped it disengages. Driving of I floor it to the same rpm it doesn't cycle. Why does it do this?

 

[commanderjjones]

First, the compressor does not cycle. Once the clutch is engaged the compressor regulates internally.

Second, normal speed is generally not too noticeable over back ground noise, but high speed sounds like a jet is starting to taxi. NOTE: both fans always turn the same speed.

If the clutch is slipping then first thing I would check is if the nut is loose. Unless someone has taken it apart then it may also have snap rings or missing/broken shims.

Jason

Thanks for the info'. I was thinking the same thing about the fan, so it sounds like my high speed isn't working......and I assume that the compressor cycling off is a direct result of that. I'm nearly certain this is related to me blowing that fuse because everything was great up until that point.

Is there anything besides the fan module that I may have fried? I've checked all of the fuses, but are there any other relays, etc...?

 

[cidades]

Based on the compressor does not cycle. In my car if I rev the car when I'm stopped it disengages. Driving of I floor it to the same rpm it doesn't cycle. Why does it do this?

Too much headpressure probably caused by lack of condenser cooling(fans not working correctly, clogged radiator fins), too much refrigerant gas or system contaminated with atmospheric air.

 

[DanG144]

Thanks for the info'. I was thinking the same thing about the fan, so it sounds like my high speed isn't working......and I assume that the compressor cycling off is a direct result of that. I'm nearly certain this is related to me blowing that fuse because everything was great up until that point.
Is there anything besides the fan module that I may have fried? I've checked all of the fuses, but are there any other relays, etc...?

The statement given that our systems should engage the AC clutch once upon startup and never disengage it again until shutdown is correct. If it is doing anything else you have a problem.

With water spray over the condenser coil, fans and speed should not matter - the water will keep it from getting too high a temperature and thus too high a pressure. If your compressor was slipping the clutch then you have a different issue.

One could be bad clutch or coil. Not getting enough seating force and friction. This is very unusual.
It could be high internal resistance inside the compressor. You should be able to turn the compressor easily with one finger when the engine is shutdown. Smooth, no catches.

Is there any chance your system is overcharged? Too much refrigerant causes the high side to be come over pressurized due to becoming essentially full of liquid - which does not compress well. When this situation occurs what you normally get is a rapid on and off cycling of the clutch as pressure hits 450 psi, the clutch disengages, the pressure rapidly drops to 350 psi and the cycle repeats.

A similar pressure cycle occurs when your high speed fans do not work (if you are not cooling it with a water spray). When the fans try to shift to high speed they stop instead. Pressure rises, clutch secures, pressure drop is slower, pressure rise is slower so cycle time is longer.

The relief lifts on the compressor at 550 psi.
Normal summertime high pressure condition is under about 300 psi, in pretty bad conditions.

If your high speed fans don't work, then as soon as you start driving and get a breeze on the condenser (assuming normal charge) the pressure drops, the AC starts working.

In all of this remember the HP sensor translates the system pressure into an electrical Pulse width modulated proportional signal. If it is bad - or has too much error you have to figure that out - the car cannot.



I don't have time this morning to reply to all of the others, but...

Some of you guys just need to go back to post one and read the PDFs for fan testing, and AC troubleshooting.

There is no substitute for a set of AC gauges to read the high and low side pressure during operation for troubleshooting. None.

 

[commanderjjones]

If I had time I'd post a video, but my clutch is definitely slipping, so I'm going to start by replacing it. It seems highly unlikely that the blown fuse issue would have caused the clutch to start slipping, but maybe it was already on it's last leg......or maybe the timing is purely coincidental. Water spray on the condenser seemed to make the AC work a little better, but only slightly, and the clutch was still cycling on and off about every 3 seconds.

The system "shouldn't" be overcharged. It was professionally charged about 2 months ago and worked flawlessly for over a month......once I determined that the pressure switch was bad and replaced it. So I know that the pressure switch WAS good, but I'm wondering if I fried it when I had the blown fuse episode.

Ambient air was cooler (relative term) this morning and my AC was working well when I left the house, but it was barely working by the end of my 45 minute drive to work.

 

[DanG144]

I agree that it does not sound as if the system is overcharged.
I too wonder if the hp sensor is bad. It is best to read the duty cycle it puts out while reading the pressure on a gauge, and ensure they agree. There is info in the PDFs linked in post #1 for the correlation.

 

[commanderjjones]

......You should be able to turn the compressor easily with one finger when the engine is shutdown. Smooth, no catches........

Let me make sure that I understand that correctly. So even with the belt still on the pulley (and key/engine off), I should still be able to spin the compressor freely? That makes sense, since there would be no engagement without the coil energized, but I want to make sure. How much resistance should I be feeling? The compressor spins without binding or catching, but there is a moderate amount of resistance. It's not like I have to strain to turn it, but it doesn't spin "easily" or freewheel. Spinning it with one hand is not a problem, but trying it with one finger might be a stretch.

 

[DanG144]

It will not free wheel, but it should spin easily when the 14mm shaft nut is grasped with thumb and forefinger. Just 3 or 4 inch pounds, at a guess. i have never tried to measure the force it takes to rotate it, and it is dependent upon how fast you rotate it.

This test is done on a car that has not been run overnight - so there is no differential pressure across the compressor - the high side and low side are the same pressure.

Can you try it on a known good one to compare?