AC Woes. few things checked, what next?

What up council?

AC quit at the end of last summer, i just dealt with it since it was the end, but anyone around here knows you can't go a full summer without AC around here. They sure didn't make this compressor easy to get to, and the AC system complicated. Never had to deal with a FCM in my Z or all this other electrical stuff, as it just uses a clutch fan, compressor, and a pressure switch. that system was way easier to diagnose and fix.

My compressor is not kicking on.

I've checked a few things.

1. checked low side pressure. was good. around 40 lbs (so I'm not dealing with a leak, thank goodness.)
2. checked fans. both come on with key on 'on' and ac 'on'. (however, they do sound like i need to clean the brushes.)
3. checked the pressure switch (via replacement)

Is there anything else I need to check top side before moving to the bottom / compressor area? If not, what's next?

From what I've gathered / my experience working on cars, my next step is to put key and everything back to 'on' and check for voltage coming to the compressor from the FCM? (it won't be 12v though since the FCM lowers it from what i've read)? Then if voltage is there, plug that back in to the compressor and check resistance on the coil, it should be 1/2 ohm? Then what?

Or if I'm way off, let me know the next steps? Thanks.

When system is off, low and high side should equalize to 85-90psi both sides. 40 is low.

40 with system ON is good(ish).

That is a manual A/C system with the addition of a controller for the fan and A/c If your car is your sig car.

As stated your static pressures should be the same both sides according to ambient temp, but 85-90 is a good number.

If the pressures change when switched on, the compressor is engaging. If so the next simple test I do is to find the liquid line to the compressor, usually the larger one and mostly metal, and feel the temp of it. If the system is functioning it will be cold to the touch. If it is just cool, likely a little low on freon.

ok. I'll add some 134 to it because it was 40 with the car off on the low side. I know 100% the compressor is not kicking on, so it very well could be because it's low if 40 is low when off. which means I might have a leak. which is always a pain trying to find. Yes it is car in sig.

Some? Needs to be evacuated and correct amount added.

If that isn't going to happen I suppose one could assume there's no liquid in it since it's below the vapor pressure and add most of a full charge.

Hard to say how much without knowing how much raises an evacuated system to 40 psi.

Where'd the missing gas go???

Enabled said:

When system is off, low and high side should equalize to 85-90psi both sides. 40 is low.

40 with system ON is good(ish).

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pdq import repair said:

That is a manual A/C system with the addition of a controller for the fan and A/c If your car is your sig car.

As stated your static pressures should be the same both sides according to ambient temp, but 85-90 is a good number.

If the pressures change when switched on, the compressor is engaging. If so the next simple test I do is to find the liquid line to the compressor, usually the larger one and mostly metal, and feel the temp of it. If the system is functioning it will be cold to the touch. If it is just cool, likely a little low on freon.

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https://workshop-manuals.com/volksw...mponent_information/specifications/page_6540/

I'm assuming this is the low side, so 68.2 psi at 68 degrees?

This thread, despite it's name, gets pretty far into AC 'lectrics diagnosis.
Check your radiator/condenser fan operation NOW

Zheking said:

What up council?

AC quit at the end of last summer, i just dealt with it since it was the end, but anyone around here knows you can't go a full summer without AC around here. They sure didn't make this compressor easy to get to, actually, they did... it is VERY easy, in fact I cannot think of too many other vehicles that have a compressor as easy to get to... you can R&R one in like 10 minutesand the AC system complicated. Never had to deal with a FCM in my Z or all this other electrical stuff, as it just uses a clutch fan, compressor, and a pressure switch. that system was way easier to diagnose and fix. I am laughing at the comparison

My compressor is not kicking on.

I've checked a few things.

1. checked low side pressure. was good. around 40 lbs (so I'm not dealing with a leak, thank goodness.)
2. checked fans. both come on with key on 'on' and ac 'on'. (however, they do sound like i need to clean the brushes.)
3. checked the pressure switch (via replacement)

Is there anything else I need to check top side before moving to the bottom / compressor area? If not, what's next?

From what I've gathered / my experience working on cars, my next step is to put key and everything back to 'on' and check for voltage coming to the compressor from the FCM? (it won't be 12v though since the FCM lowers it from what i've read)? Then if voltage is there, plug that back in to the compressor and check resistance on the coil, it should be 1/2 ohm? Then what?

Or if I'm way off, let me know the next steps? Thanks.

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DanG144 has an excellent HVAC write up here, I'd look into that. It is not nearly as complicated as you probably think it is, and EVERYTHING is easy to get at.

Often times the best test is to top it up with dyed freon, no leak stop though, and see what happens. Chances are it has lost enough to trip the low pressure switch. If it has any pressure at all in the system just top it up no evac needed. It has been proven an evac does not remove all the freon anyway so if you do an evac and assume it is empty and charge it with the prescribed amount you will be overcharged every time.

I charge by line temperature and use pressure as only a vague reference, much like the home a/c systems . I get the hard ones that others can't get to blow cold. I get some of the street rodder retrofits with who knows what capacity and make them work.

pdq import repair said:

It has been proven an evac does not remove all the freon anyway so if you do an evac and assume it is empty and charge it with the prescribed amount you will be overcharged every time.

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Where has that been proven and can you explain the physics/thermodynamics of it?

Ambient Temperature Switch

There is an Ambient Temperature Switch (sensor) under the rain tray, just below the windshield wiper base. Pain to get to (remove wipers, pull plastic rain tray out).

It is designed to NOT let the compressor come on at really cold temps. If it goes bad, compressor won't come on. Cheap part.

It's below the vapor pressure with it off. That means it's undercharged. There's no liquid in the system at all.

From the bit I'm reading and the little I understand, it sounds like compressor is gassed up. I'd be looking at the controls, maybe the clutch thing. Believe you can tell if it engages when you say go.

KLXD said:

Where has that been proven and can you explain the physics/thermodynamics of it?

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Well there never was any "Freon" in the car to begin with, but the refrigerant it does use (R134a), has a machine spec that says X amount can be left over Y period of time, and that specification recently got even tighter (and the price of the machines went up).

You'd have to look through some recovery machine manufacturers' documentation, like Robinair and others, to get the nitty gritty of that type of thing, but a quick googling finds the current standard at 98.5%... so darn near, but not quite, 100%. The old standard I have no idea.

It would be a funcfuncfunction of how good a vacuum was pulled.

I aint going to get out a thermo book but I don't think the amount of 134 left in the system at a crappy vacuum level of say 25 inches is going to make a bit of difference on the recharge amount compared to a system pulled down to 50 micron.

Bob, if there's a drop of liquid it there it'd be higher, 90ish as mentioned above with the system off. Once there's any liquid at all the pressure won't change until it's way overcharged and there's 100% liquid. Again, talking about it being off.

I'm not saying his pressure switches are good. Just that based on his pressure reading with the system off it's way undercharged.

X2 for the 134a with leak detector and a black light. I don't know about the newer VWs but the older ones like mine have a rubber ball in the valve holding everything in. The rubber gets old and leaks. I've watched my son fix one that the owner couldn't find the leak. It had the leak detector in it. When he lit up the front of the condenser, it looked like a murder scene. A little rock had caused a minute hole but it had puked its guts out on the front of the car.

KLXD said:

It would be a funcfuncfunction of how good a vacuum was pulled.

I aint going to get out a thermo book but I don't think the amount of 134 left in the system at a crappy vacuum level of say 25 inches is going to make a bit of difference on the recharge amount compared to a system pulled down to 50 micron.

Bob, if there's a drop of liquid it there it'd be higher, 90ish as mentioned above with the system off. Once there's any liquid at all the pressure won't change until it's way overcharged and there's 100% liquid. Again, talking about it being off.

I'm not saying his pressure switches are good. Just that based on his pressure reading with the system off it's way undercharged.

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I agree, the recovery machine margins are not really in play here.

Normally, with R134a a leak ends up being an "empty" system. Fortunately, leaks are not very common with these cars. Nothing with any pattern failures for sure, unlike many other brands, where an empty system is easily diagnosed because the same component is a well known trouble spot.

Usually if there is enough charge in the system to register on a gauge, it is enough to at least trigger the compressor command. If you want to at least validate the system's capacity to remove heat, and you do not have a recovery/charge machine to evacuate and recharge to a known, proper amount to insure the system is full, you can jump power and ground to the clutch connector. I would have the A/C button switched ON when you do this, with the engine running, so the fans are working as they should. And I would only engage the clutch long enough to feel that the low side line is pulling heat away (getting cold).

That will at least tell you the system can work, it is just a control side problem not letting the compressor engage.

Lots of misinformation here, but also a couple guys who kinda know a thing or two.

First of all, ALL systems leak. It is just a matter of how quickly. There is no such thing as a perfect seal in an AC system. A new car will leak refrigerant as well, but it might take 8 years for it to add up because it might be leaking literally a single molecule by molecule.
As those O-rings become old and shrunken, more and more molecules slip by and the leak adds up.
Then, of course, you could have a gaping leak like a rock punching a hole in your condenser.

Second, as said prior - if there is ANY pressure still in the system, then it does NOT need to be evacuated (vacuum pulled) and recharged. One of the things that makes an AC system particular is having to evacuate it if there is a large leak. A vacuum is pulled for 2 reasons - 1) to check for leaks (if a system can hold a 29mmHg vacuum for 45 mins, it's probably good to be charged) and 2) to eliminate all moisture from the system due to atmospheric air getting inside (a vacuum - negative pressure - actually lowers the boiling point of water to below room temp so that it can easily be sucked out of the AC lines as vapor).

Because things flow from greater to lower pressure, if your system has ANY pressure still, then atmospheric air never got inside. Therefore it doesn't have any moisture present and can simply be recharged/topped up with refrigerant.
This is, of course, assuming that the system was properly charged to begin with. For example, someone can open the system to air, skip evacuating the system, and they can shove refrigerant in there and it will show pressure in the lines, but it wasn't done properly and must be re-evacuated.

AC systems also have a couple of sensors. They have a low pressure sensor and a high pressure sensor. If the pressure is too high, then the compressor will not turn on. If the pressure is too low, the compressor will not turn on.

Personally, if I knew the compressor isn't kicking on, but the system has SOME pressure, I would proceed with re-charging it (maybe with dye) as mentioned above and see what happens. Get the pressure into the proper range and see what happens.
Usually the compressor does not go spontaneously, catastrophically bad. The compressor uses an oil to lubricate its pistons and cylinders, so they can be subject to damage if that lubricant escapes somehow. This takes time and creates lots of noise in the process.

Problem is that these cars need to be charged by weight, not pressures. So if you have a system with some charge in it, you are guessing how much to put into it. Proper way is to evacuate and measure how much goes back in with a scale.

turbocharged798 said:

Problem is that these cars need to be charged by weight, not pressures. So if you have a system with some charge in it, you are guessing how much to put into it. Proper way is to evacuate and measure how much goes back in with a scale.

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Exactly, which is really true of any car. The issue with pressures is that they are variable. Ambient temp, road speed, load (which given the nature of a variable displacement compressor working with an expansion valve... two "elastic" components right there) and other factors mean pressures can be subjective.

There are charts, and all that, but again that doesn't apply to every car. Unless you have another identical car on an identical day to compare to, it is not very scientific.

Measurement with a proper machine, by weight, is always best. That is how they do it in the factory, and that is how all the major manufacturers specify filling the system. At MB we were strictly forbidden from just "adding" R134a.

I have been to several service schools on A/C and now the big names are admitting that their machines do not completely evacuate the system. Some do barely better than 50%. There is even a new government spec that the newer machines have to meet and the good ones with a double or triple pull might get into the 90% range. couple that with decreasing size of systems (some take less than a pound)and an overzealous tech over-oiling a system and charging by spec you have a system that will not cool.

I have been charging by temps for years. If you have a system that meets the temp differentials across the evaporator and condenser within the specs, you have maximum cooling available from that system. Pressures and amounts of Freon required are merely good starting points for reference.

I have had problem cars that have come in and they had the "proper" evac and recharge done to no avail and I find them almost always suffering from overcharge and/or over oiling or other simple problems. Many have been diagnosed as needing major components like compressors, condensers etc.

I can't say I have had too many problem child VAG products over the years. Pretty much always poor cooling is easy to find. And on the ALH cars, typically the A/C either works or it doesn't. If there is anything inbetween, it is generally a dead cooling fan (or both dead cooling fans), a severely neglected cabin filter, a rotten chunk of foam fell over the evaporator core, or some moron installed a Chinacool expansion valve (for reasons unknown to me).

But I admit I have also always had use of top notch equipment, never any clunky old school scales or vacuum pumps, and our machines have never been all that old. I think our oldest machine now is as old as we've ever had, and that is about 7 years. Our newest machine is 2 years old. We also have one for the hybrids which is a whole other layer of specialty. And it wasn't cheap.

But this is all a non-issue, since the OP's compressor clutch is not even engaging. I could have probably had the system diagnosed and fixed and working fine by now, LOL.

True, VAG cars, or any car that has been engineered properly work well. Often times I have seen misdiagnosis or crappy parts installed due to misdiagnosis as the problems. I do feel sorry for the owners of those afflicted cars but....

If you have the proper temp differentials you know the system is sound and if there is no cooling you have blend door or other issues mentioned above.

evaped and filled the system up (24 oz via 2 12 oz cans per FSM of 750g +/- 50g), AC kicks on, but not near as cool as it should be and low side pressure is off the charts. The fans kick on (they did sound rough though when I did the normal key in on position test and the fuse block is melting, which I'm taking it to mean too much resistance in the fans. Just go ahead and change the fans, or try and clean the brushes? Reason low side would be super high? compressor failure (i mean whole compressor, not just the clutch right?)

Opted to just go ahead and order some fans on rock auto that had a lifetime warranty. Would prefer OEM, but can't beat a lifetime warranty, so when they eventually start failing again, which they will, I'll just warranty them. And the price wasn't bad eithr

Low side AC pressure is crazy though. I'm guessing it's the actual compressor failing. Will probably just run it this summer until it fails (might make it the whole summer, who knows). And then just replace compressor, dryer, expansion valve, etc etc.

Ahh.. the lifetime warranty... a lifetime of R&Ring them, LOL. What is really neat about Chinacool fans is that they not only fail, but they can blow apart and send the fan blades right through the radiator! That's always a fun one.

oilhammer said:

Ahh.. the lifetime warranty... a lifetime of R&Ring them, LOL. What is really neat about Chinacool fans is that they not only fail, but they can blow apart and send the fan blades right through the radiator! That's always a fun one.

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As they say on PUBG.. "CHINA #1!!!!" but it's Taiwan THANK YOU VERY MUCH.. lol. it's TYC, they've been around awhile and make parts for International, Ford, Jeep, and a few other big names so meh, if it blows up and through the radiator, they can R&R one of those too.

Save the old fans, they can sometimes be refreshed.

Low side being too high is likely compressor failure (or its regulation valve). Not fans. Fans 'cool' the high side.

Expansion valve can rarely cause it too, but less likely.

back from the dead. Went to charge the AC system for this summer. Got 1 can in (340g). compressor still didn't kick on. started on can #2. got to a point where it wouldn't suck anymore in, compressor still didn't kick on to suck more in. Think the compressor is dead?

note, compressor worked at the end of last summer until refrigerant got too low for it to kick on via pressure sensor (I'm guessing that's why?), took about 2 months before it got to that point (so it's a slow leak) and at that point it was cool enough to not need AC (UV shows the leak at the compressor as well, I think from what I could see on the top side), and there was some pressure in the system before I evaped this time.

any other suggestions to check before I just grab a compressor, dryer, and expansion valve?

yes I know there is an AC thread but it mainly talks about fans from what I saw.

also, trying to figure out if i need the sanden or Nissens? (or is that just brand preference?)

https://www.idparts.com/advanced_search_result.php?keywords=ac+compressor

I've come to the conclusion AC just isn't meant for my life probably. maybe I should move to Alaska. Home AC was dead tonight when I got home from the office to start this project. and Xterra AC wants to blow hot after about 25 minutes of sitting still idling when you're getting a lap dance and hummer around high noon at 100°. the only AC system that's solid is the Z after 10 years.