Check your radiator/condenser fan operation NOW

Hi Dan,

Thanks for this really thorough piece. I am learning a lot about the A/C, and hoping to be able to fix it myself.

2000 Jetta

My PS side fan doesn't come on (slow or fast), but my DS fan does work. The compressor works as well. (I hear it engage, and I can see the left-most part of it spin) If I understand correctly, this means my referigerant levels are good (checked low pressure, it is 26psi).

But, shouldn't my A/C work (it only blows out HOT air) with only one fan working? What does this lead you to beleive?

Thanks in advance! 100+ day today, here in Raleigh NC!

Your low pressure this time of year should read about 70 to 100 psi or higher.

Is the internal piece of the pulley part engaging and staying engaged? 26 psi might let it engage momentarily, but it would probably only be for a moment.

You are correct that if the single fan not running was your only problem, the AC would blow cool. The compressor would be working against a higher pressure and at a higher temperature, and efficiency would be down, but not enough for most people to notice.

Look at the pulley on your A/C compressor, with the engine off/key off. Note how the outside of the pulley is locked by the belt. The inside of the pulley should turn easily by hand.

When the A/C is running with the engine on, the inside of the pulley should spin. When the A/C is turned off you should see the inside of the pulley stop spinning.

To see all this you need a good light, and you need to stand on the passenger side of the vehicle looking in. Night, evening or morning may make it easier to see.

Dan

Thank you, Dan for the quick and detailed response!!!!

The internal pulley on the compressor IS engaging, and stays engaged. I tested it for 5+ minutes in 100 degree weather.

Regarding pressure, I tested the valve closest to the very front of the car, which I believe is the low valve. I did it according to instructions on the can of r-134a I bought. Also, on page 4 of your A$ AC Control Circuit Troubleshooting guide, it says psig should be about 27-130. Am I reading wrong or making a total newbie mistake?

Fuse test results:

Fuse 5 - Good
Fuse 16 - Good
Fuse 25 - Good (but VERY VERY HOT!)
Fuse S164 - Good, no melting
Fuse s180 - Good, no melting

Would Fuse 25 being very hot have anything to do with my problem? It's still good, just hot to the touch.
Thanks again. I am glad to paypal you some cash in return for your efforts. This might save me a ton of money.

I am guilty of poor communication; I made an unwarranted assumption.

With the A/C off and the engine at ambient temperature the pressure in the system will follow the table in the A4 Air Conditioner troubleshooting guide. As the temperature goes up, the pressure goes up.

As temperature goes up, pressure goes up.

The only time that the low side pressure has anything to do with the high side pressure (where the pressure sensor is) is when the compressor is shut off. I have never intentionally published what should be a good operating pressure profile for a compressor. This can get tricky. The 27 to 130 psi was intended to be the range of pressures that you might see on an idle system from 35 degrees to 110 degrees ambient temperature. The pressure is determined by the actual temperature.

So were you getting 26 psi with the compressor off at ambient temperature? Or was that with the compressor running?

To evaluate what is going on with the compressor you will have to read the high side and low side pressures. I am far from an expert on this.

There are tests written in the Bentley manual and Repair manual for evalutating the compressor operation. The very first step is ENSURING you have the normal charge in the system by evacuating the system to completely remove the charge, then put in the exactly proper weight of refrigerant, then evaluating the compressor reading during various tests.

Many of our compressors are SD7V16 Sanden compressors. These have control valves in them that adjust the compressor's stroke - and they often fail. If your compressor sounds normal, engages normally, but has very low differential pressure that might be the problem.

The fans on the MKIV are wired in parallel. When moth my Jetta's had just the small fans working I thought the fan controller ran them independently.
I disected the big fan motors and found the plastic brush holders had melted and held the brushes from contacting the armature. I freed the brushes but the crimp tabs that were bent back to remove the motor back had broked off. A tig weld spot on each tab after the fix held the back on and they have been working for 30K.

We've had near record temps here the last week or so - just in time for my AC to stop working. I checked under the hood and sure enough, it appears that my driver's side fan is not working at all. I unplugged it and hooked it straight to the battery and was unable to get it to run in fast or slow mode. Just as a sanity check, I only need to jumper the positive terminal from the battery and a ground, right? It seemed kind of strange to me that I wouldn't have to connect the negative terminal to something, so I just wanted to double-check before going further.

Thanks!
-Lee

Pin 1, near flat end, is positive for fast speed,
Pin 2, in the middle is positive for slow speed,
Pin 3 must be negative battery terminal or ground.

I usually use the battery terminals.

One fan not working will not stop your AC from working - it will just be slightly less efficient - most folks would not notice the difference in performance.

You must have something else going on, too.

Is your AC clutch engaging?

Dan

DanG144 said:

Pin 1, near flat end, is positive for fast speed,
Pin 2, in the middle is positive for slow speed,
Pin 3 must be negative battery terminal or ground.

I usually use the battery terminals.

Click to expand...

Ah ok. Thanks. I'll try again this evening using the negative battery terminal instead of ground.

DanG144 said:

You must have something else going on, too.

Is your AC clutch engaging?

Click to expand...

It sounds like it is (I hear the "click" from the engine compartment when I press the AC button). Plus, as long as I keep the fan switch on 1 or 2 I get relatively cool air in the mornings. If I bump it up higher than 2 or try to use it in the afternoons when the car has been sitting in the heat all day I get warm to hot air.

I checked the pressure on the low side (with the compressor running...I think) and it was over 100 PSI, but I figured that should be pretty close to correct with temps > 95 degrees outside.

100 psi is about right for the suction pressure when the compressor is not running.

If you have this when it is running, then it will not be cooling very well at all. That is about 65 or 70 degrees.

Fixing your fan is a good thing to do, but it probably not solve your main issue.

If the clutch is staying engaged, then you need to get your overall mechanical system tested. To do this right, the Bentley procedure and most professionals will start off by removing the charge, evacuating the system, and putting in the correct charge.

Then you do three tests and evaluate the responses. They will help narrow down the problem.

The Sanden SD7v16 compressor has a control valve in it that controls the loading of the compressor. This can fail, causing an otherwise healthy compressor to not load and not provide cooling.

Most professionals will not work on compressors, they just replace them.

Several members of this forum have replaced these control valves on otherwise healthy compressors (not noisy) and restored complete function. These are inside the compressor, so you lose the charge when you replace it, the system then needs to be evacuated and recharged. Usually a professional will replace the expansion valve that meters the liquid refrigerant into the evaporator, and the refrigerant drier, and all O-rings that are disturbed.

All this is not cheap. You can get a kit with a new compressor for about $400 from an internet supplier. You can get a gasket set and control valve for about $60 from the same supplier. A drier costs about $30. I do not have a separate price for an expansion valve.

I will probably be doing (attempting?) my first compressor control valve replacement this weekend. Since this is an attempt to do a low budget repair, I will just replace the control valve, not the expansion valve or drier. I would not do this on my own car, because I can afford the drier at least.

Dan, please post how you replace the compressor control valve. That sounds interesting. Also, where do you buy this part?

Tx.

--Nate

Several firsts here.

First time I buy parts from www.acparts.com .

First time I try working on an AC compressor.

I will take some photos and notes.

DanG144 said:

100 psi is about right for the suction pressure when the compressor is not running.

If you have this when it is running, then it will not be cooling very well at all. That is about 65 or 70 degrees.

Click to expand...

Ok thanks for the info. I'll try to do some more thorough testing to see if I can figure out for sure whether or not the compressor is really coming on.

DanG144 said:

Fixing your fan is a good thing to do, but it probably not solve your main issue.

Click to expand...

Doh! Oh well, we'll start with the fan and go from there. Thanks for your help!

Just started trouble shooting my non operating fans. I did the quick test , (fan on low, key on, ac on) a couple of months ago and the fans would work intermitently , now I get nothing. Moved over to the fuse panel and everything looks good there, now melting , or signs of corrosion.
I think my next step now is to make sure I have a full charge in the AC system. Then I'll start testing the fans.

Thanks Dan for all your help and info related to the troubleshooting and repair.

I noticed my drivers side fan not working before I came offshore. Driving home Tuesday and start troubleshooting on Wednesday (and reading more of this post).

If it's the fan, can you get that at an auto parts store, or is it a dealership item?

I would buy one off ebay for about $80, if I did not try to clean the brush holders myself. Or when the fan fails the next time after I have cleaned the brush holder once.

This is one case where the ebay fans are the same quality as the OEM fans - nothing to write home about.

CWarner, if you wish you could test your fans via the thermoswitch on the radiator.

It is pretty easy and definitive for the fans in slow speed. This is covered in the fan testing pdf at the bottom of post 1.

If I had my own gauges I would check the pressure next, if I did not, I would check the fans via the thermoswitch before I paid someone to check the charge pressures.

DanG144 said:

I would buy one off ebay for about $80, if I did not try to clean the brush holders myself. Or when the fan fails the next time after I have cleaned the brush holder once.

This is one case where the ebay fans are the same quality as the OEM fans - nothing to write home about.

CWarner, if you wish you could test your fans via the thermoswitch on the radiator.

It is pretty easy and definitive for the fans in slow speed. This is covered in the fan testing pdf at the bottom of post 1.

If I had my own gauges I would check the pressure next, if I did not, I would check the fans via the thermoswitch before I paid someone to check the charge pressures.

Click to expand...

I will check the fans first... thanks. It figures I wait til we have one of the hottest weeks to do this ..

I just began troubleshooting the A/C problem on my '02 Jetta. No fans and no compressor/clutch engagement. So I checked pressures (which there was) and then was going to bypass the coolant sensor in the radiator.

While checking the area I found the following:



Looked like it had rubbed thru the insulation and then corroded. This is the small red wire in the connector/pigtail to the FCM.

I soldered in a wire section to repair it. Plugged it all back in and the fans worked, and the comp. clutch engaged. Woohoo A/C..

Just figured that it's always good to check things thoroughly. Not always as obvious as this though. I'm glad it worked out this way for me.

Steve

I am experiencing A/C problems as well. My A/C compressor will not turn on and both fans spin fine. All the fuses are fine and the compressor plug seems to be getting the proper voltage. The system also has proper pressure. I believe either the fan control module or G65 switch is faulty. Anyone have suggestions on where to go from here?

You must check the voltage to the compressor with the compressor plugged in to provide the proper electrical load on the circuit.

Use a safety pin through the wire and measure to ground. What do you get?

If you get 9.5 volts with the compressor plugged in, then check the compressor clutch electrical resistance. It should be 3-4 ohms.

If you get the proper voltage with the circuit loaded, then the problem is not your fan control module or the pressure sensor, it is the AC clutch or wiring.

srponies said:

Just figured that it's always good to check things thoroughly.

Click to expand...

Amen to that, brother!

Thanks to this thread I found my driver's side fan to be inoperative and un-repairable. Got a new one and installed. All was perfect until I lost all my coolant due to the lower rad hose being cut by the spinning circumference ring on the new working fan. I didn't check things thoroughly enough.

Dan you have assembled some excellent information! Have you considered organizing it into a trouble shooting flow chart?

Also do you know what RPM is slow and fast? Both my fans run and the fuses are good.

Thanks for your excellent write ups.

I was tempted to try a troubleshooting flow chart, but it would be time intensive to prepare. I already have several hundred hours in what I have done so far.

If I have a slow period next winter I might try again.

The possible interactions between all of the components get so complex that it may be of little benefit.

Dan,

Thank you so much for all your help, man. I finally broke down and took it to an A/C guy. Turns out, I was just low on r-134a! He said there was just enough in there to engage the compressor, but not enough to cool. He filled it up, charged me $41 bucks and now it's working perfect!

Many thanks, your guides and patience with newbies like myself is MUCH appreciated.

For the guy that might need a new compressor, here are a couple I found on Ebay. Some of them are OEM remanufactured.

http://cgi.ebay.com/ebaymotors/ws/e...0147435801&viewitem=&sspagename=STRK:MEWAX:IT

http://cgi.ebay.com/ebaymotors/ws/e...0132028365&viewitem=&sspagename=STRK:MEWAX:IT

http://cgi.ebay.com/ebaymotors/ws/e...0354019678&viewitem=&sspagename=STRK:MEWAX:IT

Hope this helps....

rico_law78 said:

Thank you so much for all your help, man. I finally broke down and took it to an A/C guy. Turns out, I was just low on r-134a! He said there was just enough in there to engage the compressor, but not enough to cool. He filled it up, charged me $41 bucks and now it's working perfect!

Click to expand...

I used this thread and tested all the connections with a volt meter etc etc and concluded it is the same problem you have as my best guess, so i took it to my nearest A/C repair place and they wanted $175 to "charge" up to 1lb of r134a...which included them "diagnosing" if the charge is low, or air is in the lines......i told them to go to hell.

Does anyone know where to get AC hoses for a 2000 Beetle, other than the dealership? I have a hole in the hose coming off the Dryer.

Try BTCost on the forum.

Dan

I know this might sound like a dumb question initially, but here I go, Both my fans were not working at all so I pulled them both out. if I don't use my a/c except on the highway is there any reason I need to replace them? Will the engine run too hot without them?

The engine can run too hot without them.

Probably not as long as you are moving down the road at speed.

But in traffic. During and after climbing hills.

When pulling off the interstate into rest areas - any time you run hard then shut it off.

are we talking the two plastic fans in front of the rad here??