Jumping in with both feet, some troubleshooting questions

[castle]

Hi all!

I’m a car junkie and do all my own work but have always had others deal with my AC equipment.

That changed this weekend as I now have 4 cars that need AC work.

The one in question here is a 95 Audi 90 quattro with a 20 valve Turbo inline 5 motor swap. It can’t seem to build high side pressure. It was charging normally (or at least the same as the others I did yesterday) with the compressor running.

High side built up to about 100 and never got higher. The low side however, rose and rose. I stopped at about 85 on the low and 100 on the high

This is a “new” rebuilt compressor. Could it be as simple as it being bad?

I have had the whole system apart and had to make lines for it due to the engine swap so don’t rule that stuff out.

Would love some direction here. Thanks!

[JohnHere]

How did you charge it?

Assuming the charge is correct now, a high side of only 100 PSI suggests that the compressor isn't up to snuff unless it's a variable-displacement type compressor that's partially or fully de-stroked at the time of testing.

[castle]

How did you charge it?

Assuming the charge is correct now, a high side of only 100 PSI suggests that the compressor isn't up to snuff unless it's a variable-displacement type compressor that's partially or fully de-stroked at the time of testing.

Hi John,
I used a gauge set and charged through the low side port on the compressor. I had put the system under vacuum first and then started with a 3oz can of PAG 46 first since the system was totally empty. Then used about a 12oz can of Autozone brand R134A

the car was at idle (1000 rpm roughly) with the AC on high and recirculate

[JohnHere]

Your Audi calls for 23.0 ounces of R-134a and 8.5 ounces of PAG-46. If it still has the stock A/C system, the engine swap and custom hoses shouldn't make any measurable difference.

I have a few more questions. You mentioned that you evacuated the system, but for how long? A short time (like 30 minutes) doesn't necessarily ensure that all air and moisture are removed, especially if the system sat open for a while.

Sometimes, a new or rebuilt compressor comes with the full oil amount already added. Before installation, did you drain the oil from the new compressor, measure it...and if correct, replace it with the same amount of new oil? If the full oil charge was already in the compressor, and you didn't check it, adding three more ounces of PAG-46 would have been too much. I also wonder why you replaced the original compressor...leakage, seizure, or other failure?

Did you flush the parts that could be flushed, like the evaporator and lines (without mufflers)?

Along with the compressor, did you also replace the condenser (especially if the original compressor seized) and receiver/dryer?

You said that you charged one 12-ounce can of refrigerant (hopefully not containing any sealer or other additives), which is roughly only one-half of what the system calls for. I suggest taking it to a professional A/C shop to recover what's in there now, then have them evacuate and recharge it to the precise amount of R-134a the vehicle calls for. Then you'll know for sure that it has the correct charge regardless of the pressure indications.

Variable-displacement compressors can seem to act very strangely, especially without the precise amount of refrigerant. Even so, the pressures can throw you off depending on how much the compressor is de-stroked or not de-stroked at any given time.

[castle]

Thanks so much for the responses!
This is an odd build in that it is parts of a number of different cars.

Here’s the engine bay with some stuff out of the way (including the ducting that lives above the condenser and radiator at right)


the car is really an RS2 build - and those never came to the US so a lot had to be sourced from EU or made - like the AC lines.

The car started as a stock 2.8L V6 and had perfectly working AC. Nothing from that car remains in what you see here except the evaporator that lives on the others side of the firewall within the HVAC box.

The Condenser is from an S2 coupe and has not been tested
The Receiver/Drier is new

The compressor is actually NOT the stock Zexel because it didn’t fit the mounts on the motor. Later Audi’s used a Nippon compressor that fits the RS2 pulley system. To add to the complication, the Zexel has a speed sensor, the Nippon does not - it’s a 1 wire setup - which led me down another path of reprogramming the Automatic Climate control box to not seek that speed sensor input. Once I recoded the CC the compressor started to kick on.

The Compressor was bought off eBay as a refurbished model.

Now, to answer the questions,

I put it under vacuum for about a half hour - I read that would be long enough. Clearly not!
No additives in the R134A - though i did try to put a thimble full of UV dye in the yellow hose but got most of it on myself!
I didn’t know enough to measure the oil in the compressor - I was under the impression that the vacuum would make it need some.
Nothing was flushed.

Thanks again!

[castle]

Here’s the listing from the compressor I bought -
Now I see where it says - “shipping oil only, must drain and refill to specs” - uh, whoops
I guess, to be fair, I bought this in 2018 and it’s sat without the compressor kicking on since then. The compressor can’t have been engaged for more than 15 minutes total so far.

So maybe I start there, Remove compressor, drain fluid, start over The right way
Sorry - new guy mistakes here!

https://www.ebay.com/itm/310695809440

[castle]

Been doing some reading in the Audi forums from people who have charged these systems. Some are saying the proper procedure is to charge only through the high side. Could that be my problem?

They’re doing this by warming the R134 warmer than the high side system (car is OFF to avoid blowing the cans up) and charging that way. Is this crazy?