Damaged AC fitting bolt hole

Well, the ALH has exactly one pressure sensor and its right in front of the TXV, effectively at the high-side service port. What did your gauges show when it happened?

When you're charging the charge goes into the system and pressure rises on both sides; when the high side (where the sensor is) reaches ~35-40 psi the unit will come on. I've having trouble seeing how the pressure goes *too low* to cause it to cycle back off on the high side after that point. It's real common on systems with two switches (e.g. most "cycling" units like those on American and Japanese cars) to cycle repeatedly until you get a decent charge in them because the low side switch will cycle it off under suction -- but the ALH doesn't have a low-side sensor.

The most-likely event that I can think of to cause that would be a (quite badly) plugged dryer, which would result in low pressure on the high side AND low side -- basically all the refrigerant is stuffed in the condenser and dryer. With a low charge that could lead to cycling but it also should lead to no cooling either

That condition is rather dangerous in that if the RCV was to stick closed (no bypass) you'd blow the relief valve on the compressor since the switch would not see the high pressure condition and would probably burn up the compressor too since there'd be very little refrigerant actually circulating and thus little cooling of the compressor itself.

Yeah, I'm well aware of the pressure switch location on the car. And, as you stated with respect to American cars, the pressure switch on the Blazer is on the low side.

Well, whatever happened in the course of charging it from a 29 + inch vacuum resulted in the compressor to kicking-on and off two or three times and back on for the duration of charging (fans included). The car is used by my son for a relay vehicle for his work. So, a couple of times per week he drives from southern Ky to southern Tn and visa versa. He says the AC works great.

Ok guys, so I've done the following:

1. Checked the fuses above the battery and in the cabin-Good.
2. Tested both fans at both speeds-Good (driver's side is making a light gritty rattling sound, hopefully not on the way out. This may be the one I had taken apart before.)
3. Cleaned oxidation off spade terminals at the compressor.
4. Checked for voltage at the harness from the FCM- 9V. Should it be 12V?

Based on the results of #4, am I testing the FCM next?

I really can't imagine the compressor I installed as new 3 years ago would be bad, and I'm hesitant to supply 12v directly to the clutch without refrigerant in the system.

Harness from the FCM to where? If to the A/C clutch ~9V is normal. The clutch coil itself should read ~4 ohms.

Genesis said:

Harness from the FCM to where? If to the A/C clutch ~9V is normal. The clutch coil itself should read ~4 ohms.

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Yes, to the clutch. Ok, good.

So, am I checking the high pressure/low pressure switches then? Never done that before so I will do some reading. Maybe it really is just an issue with the low pressure in the system.

Also, wondering why I can't push the harness connector to the a/c clutch on firmly. It's possible it isn't making enough of a connection. As far as I could press it in with a zip-tie around it may not have been enough. I remember a nightmare scenario from years ago chasing after a charging issue with my Passat TDI for weeks. It turned out the alternator plug was not seating properly, quite similar to this.

There is one transducer (you can see it right near the firewall and TXV) on the high side (small hard line) leading to the TXV and it's NOT a switch -- it's a PWM-modulated transducer. You need something that can read duty cycle to test it (or VCDS, which can read what it's returning to the ECU); do not attempt to put voltage on those pins or short them. The only way to test it is either via VCDS or "in-circuit" with something that can read duty cycle (via pushing pins through the wires while it's connected, which of course you need to seal when you're done doing so!)

The compressor will not pull in if it is showing either very low (under ~35psi) or very high (over ~250psi) pressure. The former tells the system there's nothing in it and the latter is a "don't blow up" safety.

There is also an ambient temperature sensor that has to be working as well. This one has no visible reading on the cluster or similar but if the ECU "sees" a low enough reading (below freezing) from it the compressor is locked out. I suspect an open circuit on that sensor would result in a lockout as well.

I believe you can get what the ECU sees for both off VCDS but I don't remember where they are in the menus offhand -- and my daughter has her '03 at work right now so I can't go digging around looking for them.

Genesis said:

There is one transducer (you can see it right near the firewall and TXV) on the high side (small hard line) leading to the TXV and it's NOT a switch -- it's a PWM-modulated transducer. You need something that can read duty cycle to test it (or VCDS, which can read what it's returning to the ECU); do not attempt to put voltage on those pins or short them.

The compressor will not pull in if it is showing either very low (under ~35psi) or very high (over ~250psi) pressure. The former tells the system there's nothing in it and the latter is a "don't blow up" safety.

There is also an ambient temperature sensor that has to be working as well. This one has no visible reading on the cluster or similar but if the ECU "sees" a low enough reading (below freezing) from it the compressor is locked out.

I believe you can get both off VCDS but I don't remember where they are in the menus offhand -- and my daughter has her '03 at work right now so I can't go digging around looking for them.

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Thanks, don't have access to vcds.
What is the likelihood of these transducers or the temp sensor failing? I had never heard of them?

The pressure transducer has been reported to fail on occasion; it's under quite a bit of pressure normally since it's on the high side so that's not all that surprising. It's also a relatively-common leak point.

The temp sensor is more likely to be a wiring fault... Wire harness problems become more and more of an issue with age on any vehicle. I believe on your car it's under the cowling on the left side under the windshield.

Find someone with VCDS; if the ECU is seeing a bad signal from either of those you'll know which it is immediately instead of screwing around. If one of them is showing a bad value you then know what you're after and when you find it you'll also know it's fixed.

Here's the other thing though -- how'd you get 9V to the clutch at the FCM? You shouldn't be able to get that without (1) the car running and (2) all the other inputs correct for the compressor to run, because with that 9V present and a good clutch coil the compressor IS engaged!

Genesis said:

The pressure transducer has been reported to fail on occasion; it's under quite a bit of pressure normally since it's on the high side so that's not all that surprising. It's also a relatively-common leak point.

The temp sensor is more likely to be a wiring fault... Wire harness problems become more and more of an issue with age on any vehicle. I believe on your car it's under the cowling on the left side under the windshield.

Find someone with VCDS; if the ECU is seeing a bad signal from either of those you'll know which it is immediately instead of screwing around. If one of them is showing a bad value you then know what you're after and when you find it you'll also know it's fixed.

Here's the other thing though -- how'd you get 9V to the clutch at the FCM? You shouldn't be able to get that without (1) the car running and (2) all the other inputs correct for the compressor to run, because with that 9V present and a good clutch coil the compressor IS engaged!

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I thought that's how it was supposed to be done?
Car was running, plug connector to the compressor was unplugged, turned on a/c switch in the cabin with blower on 2, plugged multimeter leads into the connector-Got 9V.

So it sounds like I have my answer then? It has to be the low pressure.
I did go out and firmly press the connector on, it didn't click but it definitely can't be pulled off now so I tossed the zip-tie.
I guess I should just take it to the shop now and see what happens with freon added.

intro said:

I thought that's how it was supposed to be done?
Car was running, plug connector to the compressor was unplugged, turned on a/c switch in the cabin with blower on 2, plugged multimeter leads into the connector-Got 9V.

So it sounds like I have my answer then? It has to be the low pressure.
I did go out and firmly press the connector on, it didn't click but it definitely can't be pulled off now so I tossed the zip-tie.
I guess I should just take it to the shop now and see what happens with freon added.

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IMHO the clutch lead has to be checked UNDER LOAD (plugged in.)

I believe that is a solid-state switch (NOT a physical relay -- the fans are a physical relay as you can hear them click on and off) so with no load on it you might well see voltage from leakage across the junction (I can't go check it at the moment) yet there's no current behind it. No current, no clutch.

But what you've reported is that the shop says NEITHER the fans OR clutch engage.

There's a disconnect between what you are reporting here and what the shop is saying. With no refrigerant in the system (zero or negative pressure) the fans should NOT run and there should NOT be power to the compressor clutch.

Genesis said:

IMHO the clutch lead has to be checked UNDER LOAD (plugged in.)

I believe that is a solid-state switch (NOT a physical relay -- the fans are a physical relay as you can hear them click on and off) so with no load on it you might well see voltage from leakage across the junction (I can't go check it at the moment) yet there's no current behind it. No current, no clutch.

But what you've reported is that the shop says NEITHER the fans OR clutch engage.

There's a disconnect between what you are reporting here and what the shop is saying. With no refrigerant in the system (zero or negative pressure) the fans should NOT run and there should NOT be power to the compressor clutch.

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And that was the case, but...

UPDATE
After speaking with the manager and explaining everything that had happened since last week, he set me up to come down, and we agreed to just recharge the system. If it worked, great, if not, it would allow me to continue testing with the system full.

Unfortunately, they filled it and then called me over to show me-Clutch still wouldn't engage. I did see both fans running, so pay for the recharge and I'm on my way.

Here's where it gets weird. I get home, unplug the connector, and supply power directly to the compressor with the car running, AND the clutch engages. It seemed like it struggled at first, starting and stopping almost like it had to break through some rust before spinning consistently. This may have just been in my mind, as I struggled at first to keep my clips on the terminals. When I reconnected the plug it just started spinning no problems.
The only thing I noticed is the clutch sounds louder than it should be I think.

Hard to say what it was at this point. The clutch had never been spun in the 3 years since I had installed it, so I'm not sure if that can create a build-up internally. And if that's true, is it possible the 12V direct from the battery rather than the 9V from the FCM was the extra bit of juice needed to break the clutch free? I dunno. Hopefully, this doesn't mean I'll be due for a premature failure but I'll cross that bridge later, for now it's nice to have cold A/C again.

Thanks folks!

Since the unit was open to the atmosphere for quite some time I would not be shocked at all if the compressor is corrosion-damaged. You'll find out rather quickly if that's the case

But for now, enjoy the working A/C....

I would not be surprised if you have an intermittent connection on the clutch connector; you said the tab was broken. If so make sure it's secure; at 4 ohms there's a decent amount of current going through there, probably enough to burn it up over time if the connection is loose, never mind it not pulling in.

Oh yeah, one more quick question: Would PAG oil have been added in with the freon? I know the compressor had come pre-loaded, but would that have been cleared out by the evacuation? I totally forgot to add oil to the drier this time around.

Genesis said:

Since the unit was open to the atmosphere for quite some time I would not be shocked at all if the compressor is corrosion-damaged. You'll find out rather quickly if that's the case

But for now, enjoy the working A/C....

I would not be surprised if you have an intermittent connection on the clutch connector; you said the tab was broken. If so make sure it's secure; at 4 ohms there's a decent amount of current going through there, probably enough to burn it up over time if the connection is loose, never mind it not pulling in.

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Ugh! It was a bone-headed move on my part to leave the system open that long. Who would have thought that condensation could spread all the way to the compressor? I hope replacing the drier again was enough of a lesson. The tab actually doesn't appear broken, just takes a lot of effort to push it on. It's not pulling apart without the aid of a screwdriver now. Definitely feel like I understand the system a little better, so thanks again!

intro said:

Oh yeah, one more quick question: Would PAG oil have been added in with the freon? I know the compressor had come pre-loaded, but would that have been cleared out by the evacuation? I totally forgot to add oil to the drier this time around.

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Not normally, no. Shops know that a new compressor typically comes full of oil; the risk is typically of an oil overcharge (unless you tear a compressor apart and clean it completely out of course!) and when you flush a system the compressor is NOT flushed (you can't; you'll destroy it as you can't get all the solvent out nor clean it that way -- you have to disassemble it.)

The new compressor should have a full charge of oil in it, so if anything (e.g. you didn't flush the condenser, evaporator and lines) you're likely somewhat over-oiled -- but not a lot, because most is in the compressor. You should be fine in that regard (being a bit over will raise the boiling point and decrease efficiency somewhat but is otherwise not harmful.)

Pulling a vacuum on the system will not boil the oil at all; whatever was in there still will be in there.

Ok, so this really sucks. After having a couple of cold weeks of ac, I was driving around today and I noticed the AC didn't feel as cold, and also a strange smell coming from the vents, followed by some strange sounds. I shut the AC off, pulled over, and checked the compressor-still engaging. Got in the car and switched the vents to my legs and turned the AC on, getting cold, then all of a sudden, a loud sound and a refrigerant cloud from the front of the car. It all blew out from the drier tube connections, top and bottom. What the hell happened here? Also, areas of my skin that had been getting air from the vents feel kind of itchy/burned (this could just be in my head). The evaporator has no leaks and that would probably be the area that would expose the cabin to refrigerant right?

I'm at a loss right now. Possible it was overfilled? Blown O rings? They had checked for leaks.

Cleaner tube? Please describe.... are you talking about the dryer mounted on the rear, right side of the radiator area?

The only way refrigerant can get into the pax compartment (other than by being sucked in through the cowling after being blown out, which would be a vapor -- and it's not especially hazardous as a vapor) is if the evaporator or TXV O-rings at the evaporator (which point into the pax compartment) fail. The rest of the system is outside of the pax compartment.

Genesis said:

Cleaner tube? Please describe.... are you talking about the dryer mounted on the rear, right side of the radiator area?

The only way refrigerant can get into the pax compartment (other than by being sucked in through the cowling after being blown out, which would be a vapor -- and it's not especially hazardous as a vapor) is if the evaporator or TXV O-rings at the evaporator (which point into the pax compartment) fail. The rest of the system is outside of the pax compartment.

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Sorry, corrected. Drier tube. Did I just get a bad one?

Is the dryer itself intact or did it split?

The seals there (like everywhere else) are made with O-rings -- you did change them when you put the new dryer in, yes? Although if the bolts are in and snugged up it's pretty tough for those O-rings to extrude (and fail that way); a pinched or fatigued O-ring usually leaks slowly, not catastrophically.

That top port, however, can be cross-threaded pretty easily as there's not a lot of clearance there for the allen wrench on it, and if you cross-thread it then the fitting won't be flush and that would easily lead to what you had happen.

If the dryer itself split then it was defective - there's a relief valve on the back case of the compressor that should open before anything else blows up, and for that to happen the RCV would have to stick closed *and* the high-pressure cut-out on the switch (near the high side service port) not be effective either.

Genesis said:

Is the dryer itself intact or did it split?

The seals there (like everywhere else) are made with O-rings -- you did change them when you put the new dryer in, yes? Although if the bolts are in and snugged up it's pretty tough for those O-rings to extrude (and fail that way); a pinched or fatigued O-ring usually leaks slowly, not catastrophically.

That top port, however, can be cross-threaded pretty easily as there's not a lot of clearance there for the allen wrench on it, and if you cross-thread it then the fitting won't be flush and that would easily lead to what you had happen.

If the dryer itself split then it was defective - there's a relief valve on the back case of the compressor that should open before anything else blows up, and for that to happen the RCV would have to stick closed *and* the high-pressure cut-out on the switch (near the high side service port) not be effective either.

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I did have an issue with having to replace the stock bottom bolt on that drier (cross-threaded) with one from the hardware store, but I made sure the bolts were the same, and it did snug down ok with the new bolt from what I could tell. No issues on top but I do see a little leakage from under the fitting unless that is just from the spray of refrigerant out the bottom.

Why would everything hold together ok for 2 weeks though? I will try to go get a better look to see if the canister split. Thanks. This is really frustrating. I don't know how I'll be able to get the shop to do the vac/recharge without paying again, and I'll be paying for another drier tube it looks like.

It should be pretty easy to find where the failure happened as that sort of explosive release of refrigerant is going to carry a fair bit of oil with it, and that will be all over the place emitting from where the leak occurred. In addition the failed component itself should be obvious.

If the dryer is split it will be obvious on inspection. If it failed at the bottom junction then despite you thinking you had the right bolt from the hardware store you probably did not and it stripped out under pressure, blowing the fitting off.

There's a couple hundred psi in there on the high side when it's running (and about 100 on a really hot day with it shut down and cooking in the sun!)

Genesis said:

It should be pretty easy to find where the failure happened as that sort of explosive release of refrigerant is going to carry a fair bit of oil with it, and that will be all over the place emitting from where the leak occurred. In addition the failed component itself should be obvious.

If the dryer is split it will be obvious on inspection. If it failed at the bottom junction then despite you thinking you had the right bolt from the hardware store you probably did not and it stripped out under pressure, blowing the fitting off.

There's a couple hundred psi in there on the high side when it's running (and about 100 on a really hot day with it shut down and cooking in the sun!)

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It looks to be related to the bottom connection not being tight as you said. :/
The fitting is still on with the bolt threaded but it might be a bit loose/not flush.
The drier itself is intact and the welds seem fine. It's not possible for the hose to burst I would think?
They seem designed for high pressure. Lesson learned.

I will get fresh stock bolts this time and be extra careful with the new drier.
Hoping there is a way I can talk the guys at Sears into a free refill but probably not.

Anyone have the torque specs for the bolts on the AC/ Drier? Thanks in advance.

You're going into aluminum with that bolt, so reefing on it will strip the threads in the drier. More is not better; those are blind holes and the seal is made with the O-ring in the bore so all you need is enough torque to prevent it from backing out due to vibration. Moderately tight using an "L" style allen key should be about right (which is likely around 10-15 ft/lbs.)

I'm not sure you could get a torque wrench on the top one anyway due to interference in the immediate area and above where the connection is.

Genesis said:

You're going into aluminum with that bolt, so reefing on it will strip the threads in the drier. More is not better; those are blind holes and the seal is made with the O-ring in the bore so all you need is enough torque to prevent it from backing out due to vibration. Moderately tight using an "L" style allen key should be about right (which is likely around 10-15 ft/lbs.)

I'm not sure you could get a torque wrench on the top one anyway due to interference in the immediate area and above where the connection is.

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Gotcha, thanks. I was just thinking ballpark with an extension.

The main point is to get it completely flush and not budging? I'll aim for that.