Its HOT out, another A/C post

Hey all, Just put my project back together and I want to drive it. But....

The A/C is not working. So i decide to trouble shoot it from info i located on here.

A4 Air Conditioning Control Circuit Troubleshooting
Rev 7, 6/18/2009

Ignition on, fan on , ac on.. fans are not working.... so trouble shoot fans now.

I see this

"Low refrigerant pressure will lock out both fans and the AC clutch. "


I have no refrigerant in the system. it needs to go in and get recharged..

could it be this simple that the A/C is not engaging????

The clutch won't engage with no pressure in the system. Idunno about the fans. I would think they'd still run.

Where'd you find that info.

KLXD said:

The clutch won't engage with no pressure in the system. Idunno about the fans. I would think they'd still run.

Where'd you find that info.

Click to expand...

pulled it from here, promising if this is the case. hoping someone can weigh in..

http://pics.tdiclub.com/data/516/A4_Coolant_Fan_testing_Rev_7.pdf

which was linked from here

http://pics3.tdiclub.com/data/517/A4_Air_Conditioning_Troubleshooting_Rev_7.pdf

Here's my most recent experience with the A4 AC system..

Last summer, I installed a junk yard used AC compressor on my formally owned 2000 Jetta TDI (son owns it now). Once prepared to install the refrigerant, I started the engine and turned on the AC (Fans did not come on nor did the AC Compressor Clutch kick-in). Several minutes after refrigerant was flowing in, the AC compressor kicked-in and almost immediately the fans come on.................... seconds later they kicked-out. This scenario played out over the next few minutes until they stayed kicked-in as I finished putting in the refrigerant.

There you have it!

(Oh, and a year later, nice cold AC reports my son. I did not measure the amount installed, but based on the sticker under the hood relating to the amount of R-134a, apparently I got it within the 10% variance!)

its risky to just top it off or charge it back up. make sure you FIND THE LEAK and make sure that leak did not leak out any PAG oil.

the really only good option here is a full service.
Remove compressor, blow all lines clear of old oil with NITROGEN only, drain and refill compressor with NEW PAG oil measured out exactly
Purge with nitrogen as you hook up the filter dryer that you will need
pressure test with nitrogen, fix leaks if necessary, vacuum it down and weight in a charge properly.
as long as you didnt loss any pag oil, you can supper cool supper heat chart and refill the system but only if it still has a bit of pressure to it.
do not add anything other than plain 134a, no stopleak, no synthetic, no anything added at all, not supper forst, nothing with any ginic markings at all. Why, its all fake or if its not it hurts the system. If you try using stop leak, i can say with a sure bet that your system will fail very soon.

Yes, that's the perfect ideal scenario, no doubt!

But, thousands and thousands of folks walk in their favorite FLAPS or Box Store and purchase Refrigerant to "top-off" their AC System. Example: My 1995 Chevy Blazer (purchased new, for the wife) had exceptionally nice cold air until early-summer 2012. Then, the bearing on the compressor clutch assembly began to squeal. I took it to a certified licensed AC pro for a new AC Compressor. By late-summer 2013 after the warranty had expired, the system wasn't cooling... low on refrigerant resulting in kicking-in and out. I promptly added some R-134a using manifold gauges. When the pressures (low and high) were within spec in relation to the ambient temp as well as the return line sweating cold, I concluded it was charged within the variance depicted on the label there under the hood. I've had to re-charge it twice since. Thus, the leak must be very, very small. Oh, and to be sure, I did add some proper oil (less than 2 ounces) the last time I charged it. Yes, there is a point of too much oil as well as too little, but like the refrigerant, there is a variance!........... same as the system on the A4s.

So, assuming the OP knows some basics of Auto AC systems and has the necessary tools, what's the risk? AC manifold gauges to start with will reveal charge level. I'd start there! But, if the OP doesn't have the tools and basic experience/knowledge of AC systems, off to the pro..

I agree 100% about staying away from additives, especially anything Stop Leak! Why, early systems generally have a screen before the Thermal Expansion Valve Orifice which stop leak will clog shut. If the TXV in the A4 system has a screen, which I have no clue, you can bet the farm stop leak will clog it.

dont get me wrong, nothing wrong with topping off a system that just leaks down after a few years. my escape does this. i end up putting about 18 oz or so back into the system as there is a leak i dont feel like messing with. Its the old rubber hoses.
as long as OP can identify that there is not any oil loss at the leaking site, then topping it off is fine.
134a is forgiving and going with pressures at temp via a chart is fine.
hvac 101 is really easy to do now that youtube exists.

Awesome thanks guys. Im gonna bring it into a shop and have them recharge it.

The A/C in the Jetta stopped last year. If I pushed on the A/C button it would sometimes work, but mostly not. Come to find out, it was a part of the dial setup assembly that had failed. Replaced that and now we have nice cold air.

Right, so I thought id update so this isnt just another thread that stops with no result.

I picked up some A/C in a can.. couple cans and i think it cost me around $40 canadian.

Started the car, fan on, A/C, recycle... then connected the can. As soon as I squeezed the trigger, the compressor kicked in. I charged it up to the spec on the can and called it a day.

My A/C is so damn cold, its almost too cold. I should have done this back in the spring.

finally a win.... now to fix the short to ground so i stop melting clocksprings, and the cv joint, etc...

If it's leaking it will leak again. You have no idea how much is in there, but it's less than a full charge since if it was low enough not to engage it was well under half, and one can is about half.

Anyway, find the leak. Get a UV light and have a look around. It should show up.

Glad it works.

So how much did you put in out of that can? Was the gauge reading any pressure before you added some?

I didn't reread all the above. Was there still some pressure in it? Was the system ever opened up?

KLXD said:

Glad it works.

So how much did you put in out of that can? Was the gauge reading any pressure before you added some?

I didn't reread all the above. Was there still some pressure in it? Was the system ever opened up?

Click to expand...

So I spoke with the old owner, and he was telling me he replaced the heater core and compressor shortly before I picked up the car and the ac was discharged when this happened.

Not knowing everything meant i was very concerned when the compressor failed to start when i turned on the ac. but through research and posts here i determined that it was a safety thing.

I used AC on the go https://www.princessauto.com/en/detail/a-c-on-the-go/A-p8726903e and just worked to their instructions. kept it charging in the blue zone and its great.

I chose this over Red Tek because the information was redily available and simple to use. Also, it has an oil mix in the can and i wouldnt have to worry about adding it myself. I did a lot of research on red tek and found that most people couldn't grasp that the 12a was a replacement and every question became an argument and debate. I ended up using about a can and a half which is what the mk4 takes based on the sticker on the front panel and online.

I will see how long this lasts. if it gets me through the rest of summer it was money well spent

DieselDuberrr said:

So I spoke with the old owner, and he was telling me he replaced the heater core and compressor shortly before I picked up the car and the ac was discharged when this happened.

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Sounds like the system was not evacuated and the dryer not replaced.
If so it is not good for the system long term.

If you want to gamble with it let us know how long it works.

Yep, that's what I was getting at.

That system needs to be drained, dryer replaced, vacuumed, and the correct mass of refrigerant added if you don't want to destroy it slowly.

ToxicDoc said:

That system needs to be drained, dryer replaced, vacuumed, and the correct mass of refrigerant added if you don't want to destroy it slowly.

Click to expand...

Thanks for the tip. it'll last the summer thats all i care about at this point. many jobs to complete over the winter anyway...

DieselDuberrr said:

Thanks for the tip. it'll last the summer thats all i care about at this point. many jobs to complete over the winter anyway...

Click to expand...

dont put it off too long. the moisture is what ruins everything

DieselDuberrr said:

Tek because the information was redily available and simple to use. Also, it has an oil mix in the can and i wouldnt have to worry about adding it myself. I did a lot of research on red tek and found that most people couldn't grasp that the 12a was a replacement and every question became an argument and debate. I ended up using about a can and a half which is what the mk4 takes based on the

Click to expand...

DieselDuberrr said:

pulled it from here, promising if this is the case. hoping someone can weigh in..

http://pics.tdiclub.com/data/516/A4_Coolant_Fan_testing_Rev_7.pdf

which was linked from here

http://pics.tdiclub.com/data/517/A4_Air_Conditioning_Troubleshooting_Rev_7.pdf

Click to expand...

Hi - I found this post from last year. The issue I have is that my daughters 1999 NB TDI cooling fans will not run. I checked the fans first (they both work hi/lo speed) and then jumpered the thermal switch and the fans work correctly there too. I suspect the AC refrigerant is an issue after reading this post. It is a bit troublesome for me to think that loss of refrigerant would cause an overheat of the engine because the cooling fans are locked out from operating. This doesn't make good design "sense".
I'll still debug this further - I find it interesting that when I bought the car the AC did not work and the fans ran ok....I think. The AC was completely discharged in that case. Hmmmm.....

If the A/C is completely discharged the fans will NOT run except under thermo-switch control (e.g. when the coolant is hot enough to require it.) There is one pressure sensor (PWM, it's not a switch) and if it reads below minimum the compressor will not engage and the fans will not run with the button in, fan to any setting but "OFF" and the ignition on.

MANY years ago I had a car that occasionally would overheat coming off the highway; the culprit was the connection at the thermal switch in the radiator. Most of the time it worked properly, but once in a while it would not signal the fan to come on, even though it was required. It was NOT fun to find the actual problem and fix it; it turned out to be in the wire a decent distance from the connector itself. I would be rather suspicious in your case that this is what is happening. With a diesel it's especially bad because even mild overheats have a habit of doing severe damage (E.g. head gaskets, cracked heads, etc.) to them.

I inspected the connector to the FCM and it looked as though it had a little corrosion on one of the fan power pins. Cleaned that up and tested the system by jumpering the thermal switch. Everything checks out so far.
I also cleaned the connector for the thermal switch. I am going to put it all back together to see if it made any difference.
I'll visually check the harnessing as well.
Thanks!

I topped off my A/C this year because my ALH would a take a few minutes to blow cold air and it fixed the problem. A/C worked fine for short trips around town. Then I took it on a 23 hr drive to Seattle and it kept freezing up every 10 mins. It was so annoying and I had to deal with that there and back. I even bought a set of gauges on the trip and tried to get the charge right, no success. When I got back home and had all my tools, I vacuumed out the system and put the correct amount of charge in it, it has been working perfect since. I will never top it off again after that experience.

mrfiat said:

.....Then I took it on a 23 hr drive to Seattle and it kept freezing up every 10 mins. ......... I will never top it off again after that experience.

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Well, the reason the AC system was freezing-up is due to low refrigerant. So, you never had it "topped" off. The R134a systems require fairly close to the exact amount to work properly. So, if the system is low (obviously a leak), then it will be quite difficult to put in the correct amount. The best way is to have a manifold gauge so you can watch the low and high side pressures in relation to the ambient temp (all very important). Typically, at 85f ambient temp, the low side pressure should be about 45 psi (a little less or more is okay). The high side pressure should be at least 250 psi while the low side is at the 45 psi range. Most systems have a sticker that shows the amount of refrigerant it holds, with a + or - amount.

Andy, I appreciate your insight on this matter, but I'm sure I had way more than the required amount of R-134a in the system and it kept freezing up. Once I got home and removed all the R-134a out of the system and recharged it with the correct amount, it worked perfectly. I put way more than 2 cans in.

Interesting thread. I did an experiment at the suggestion of a friend, who is a former HVAC tech (he's been a large displacement diesel mechanic for over a decade now). Properly evacuated R-134a from my mom's BEW and put in R-152a. If you don't know what 152a is, it's the compressed air canisters one would use for blowing dust out of keyboards. I currently have it running in several refrigerators as a replacement for SO2 and R-12 and it works fantastic. Worked great in the BEW (2/3rds the weight of that specified on the core support label), but I have a leak in my system, so I need to find and fix that (we didn't find anything going to the evap, so I'm thinking it could be my condenser).

Check the leetle black rubber hemispheres on the service valves for a leak. Look like a ball but they're not. Might get lucky.