Assistance with AC Issue. - PeachParts Mercedes-Benz Forum

michael_j_brown · #1 06-21-2020, 07:03 PM

I’m working on the AC of my 83 300D. I’ve had the car for several years and the AC has never worked since I owned it. This weekend I installed a brand new compressor, receiver dryer, expansion valve and o-rings.

The system is holding a vacuum. While attempting to charge the system several bizarre things are going on:

1. High side stays at zero
2. The pressure on the low side increases as the coolant goes into the system.
3. The compressor never turns on

I verified that the compressor is clicking on if you bridge the wires on the pressure sensor on the dryer/receiver. I attempted to load the system with refrigerant by manually controlling the compressor, but I got the same result and the compressor was not happy.

I thought maybe there was a blockage on the high side so I pulled the lines from the condenser but that seems to be fine. I also blew some AC cleaner through those lines and I did the same going from the receiver dryer back down to the compressor.

Anyone have a clue what might be going on?

ROLLGUY · #2 06-21-2020, 09:17 PM

So many questions, I don't know where to start. First of all, did you flush the entire system (evaporator, condenser, remaining hoses) BEFORE installing the compressor? What oil, and how much did you add to the system? What refrigerant are you using? If R134a, are the charge fittings new? Did you remove the Schrader valves from the R12 charge ports? Did you replace the pressure switch? Did you use dry gas to pressure test the system to check for leaks before charging? (Pulling a vacuum is NOT the correct way to check for leaks). Have you replaced any (or all) of the 25+ year old hoses?

Automotive A/C systems diagnosis can be complicated, especially when the work is done by a non-professional (no judgement here, this is just a fact). There are so many things that have to be done properly, and in the correct order for these systems to work properly, and last a long time. Then there is my opinion that many (if not all) rebuilt R4 compressors are junk. New R4's are not much better. One may get lucky and get one right out of the box that works for a season. So many DIY'ers don't know how important oil is for this type of compressor, and it most always ends up in disaster.

Of course I am a little biased (or maybe a lot), because I have had my fill of bad R4's (new and rebuilt), and have gone all out with the Sanden route. Never again will I install an R4, it is a waste of time in my opinion.

Be that as it may Mr. Brown, I suggest you get an opinion from your local A/C shop before continuing with your A/C. At least have them pressure check your system, and better yet, the vac and charge as well. If they will work with you, you can do all the mechanic work, and let them do what they do best.
Of the 50+ A/C jobs I have done (99.8% MB Diesel cars), ALL of them have had the leak check, vac, and charge done at my local A/C shop. For me, it is money well spent in my opinion......Rich

michael_j_brown · #3 06-21-2020, 10:28 PM

Quote:

Originally Posted by ROLLGUY

So many questions, I don't know where to start. First of all, did you flush the entire system (evaporator, condenser, remaining hoses) BEFORE installing the compressor?

Yes, I used ac pro cleaner

What oil, and how much did you add to the system?

The compressor came with 3oz of PAG 100, I added 5 oz for a total of 8

What refrigerant are you using? If R134a, are the charge fittings new?

R134a and no, I did not change the fittings. I will do so tomorrow.

Did you remove the Schrader valves from the R12 charge ports?

This is such an obvious thing to look at and I’m embarrassed to say I did not pull off the R134A adapters. They were on the car when I purchased it.

Did you replace the pressure switch?

No, but I ordered one it will be here tomorrow.

Did you use dry gas to pressure test the system to check for leaks before charging? (Pulling a vacuum is NOT the correct way to check for leaks).

No I did not use gas.

Have you replaced any (or all) of the 25+ year old hoses?

I examined the hoses and they seemed fine so I did not replace them.

Automotive A/C systems diagnosis can be complicated, especially when the work is done by a non-professional (no judgement here, this is just a fact). There are so many things that have to be done properly, and in the correct order for these systems to work properly, and last a long time. Then there is my opinion that many (if not all) rebuilt R4 compressors are junk. New R4's are not much better. One may get lucky and get one right out of the box that works for a season. So many DIY'ers don't know how important oil is for this type of compressor, and it most always ends up in disaster.

Of course I am a little biased (or maybe a lot), because I have had my fill of bad R4's (new and rebuilt), and have gone all out with the Sanden route. Never again will I install an R4, it is a waste of time in my opinion.

Be that as it may Mr. Brown, I suggest you get an opinion from your local A/C shop before continuing with your A/C. At least have them pressure check your system, and better yet, the vac and charge as well. If they will work with you, you can do all the mechanic work, and let them do what they do best.
Of the 50+ A/C jobs I have done (99.8% MB Diesel cars), ALL of them have had the leak check, vac, and charge done at my local A/C shop. For me, it is money well spent in my opinion......Rich

I will see if there is a good AC shop around and I’ll have them take a look at the vehicle