AC troubleshooting help, please? - PeachParts Mercedes-Benz Forum

Demothen · #1 06-05-2016, 04:36 PM

Hi all, I just took my 85 300d into the shop to charge the AC, while the gentleman was charging it, he pointed out that the high and low sides were both gaining pressure when it cycled on. The compressor was getting surprisingly hot, and occasionally squealing the belt (or maybe the clutch). I suspect I already know the answer, but are these all symptoms of a failed/failing compressor? If so, I am guessing its time to change the compressor, flush everything, and replace the receiver/drier. Is this correct?

Unfortunately I simply don't have the money to to upgrade to a Sanden compressor and parallel flow condensor. I live in a fairly moderate climate and don't plan on driving this car on extremely hot days, and will likely only own it for a few years. Because of this I plan on just going with a new R4 compressor.

leathermang · #2 06-05-2016, 04:58 PM

Uh.... not for sure yet.....
are you sure the belts are in good shape and properly tightened ?
Are you sure there was enough air being provided to the condensor ?
Are your electric fans and your engine fan working correctly ?

what did your service guy suggest was happening ?
what were the actual pressures which were showing ?
what was the temp at the center vent with the blower on LOW ?
were the windows open ?
what was the ambient temperature at the time of the test ?

Demothen · #3 06-05-2016, 05:28 PM

Belts are in good shape, seem properly tightened. They only squeal when I am driving. Have a new belts I will install as soon as possible.
Engine fan was running, electric fan is freshly rebuilt and tested, but never kicked on.
Service guy was baffled
Did not notice actual pressure. Did not even get one full can in.
Had blower on high, temp set to low: ambient air temp at middle vents (approximately 88)
Ambient temp was about 88 degrees, we were working in a shaded shop area.
I can hook up my manifold later this week and test it again.
Fyi, new receiver drier, new expansion valve, new pressure switch. Also new CCU, vacuum pods. We vacuumed for 20ish minutes and it held with no leaks. The shop does not have a dry nitrogen system to pressure test, no shops I have found locally have mentioned using one. Am having problems with the monovalve, will be ordering one from Mr. Murphy tomorrow, sick of fighting it. I did put my hand on both lines at the expansion valve, both were at or very slightly cooler than ambient. Didnt check with IR thermometer.

Thank you for your time.

SD Blue · #4 06-05-2016, 05:36 PM

Did you do a flush of the system before connecting to the compressor?

Sounds like possibly a blocked expansion valve.

leathermang · #5 06-05-2016, 05:52 PM

Ok.. multiple problems with your test...
windows need to be open
blower fan needs to be on LOW ... test thermo in the center vent...
electric fans in at condendor need to be ON.

Vacuuming is not for leak checking ... it is for boiling the moisture out of the system...
What refrigerant are you using ?
what are you using to seal joints when you put it all back together ?
how did you determine how much oil was in the system or whether you needed to add oil when you replaced those items ?

Demothen · #6 06-05-2016, 06:28 PM

Windows were open, forgot to mention that
Will set fan to low next time.
Should i bypass the temp switch to run the aux fan next time?
I understand that vacuuming is not a valid leak test. Unfortunately of the mechanics I trust here who are willing to work on it, none offered/mentioned nitrogen fill to leak test, and I really don't trust any of the other local shops to do the work. Dealer is out of my budget.
Using 134a.
Using new green o rings at every joint I touch (134a compatable ones, don't recall what they are called off hand). Using a bit of oil on each O ring before tightening the fittings.
All local mechanics said to just leave the oil it had in the system where it was, since I did not change compressor.

My hope was to do a "cheap" fix since the system worked before (just not very well). The old expansion valve leaked, and I only got cold air on cool days (45f air on 70f days). Unfortunately I was overly optimistic, and now I will replace as much of the system as possible on my budget.

I just ordered a new r4 compressor and receiver drier. My pressure switch had been installed literally for a few hours, so I see no reason why I couldn't transfer it over - with new O rings of course. My expansion valve is also new. I may go ahead and replace that as well. I will be pulling the compressor, dryer, and txv, flushing the system, and replacing the above listed parts. I will then see if anyone locally is capable of performing a dry nitrogen pressure test, vacuum the system, and have it refilled again. Before all this I will read through your guides again.

Thanks all

Demothen · #7 06-05-2016, 06:42 PM

Oh, one quick question - does anyone know about how long it would take for a person to pull swap compressors on a 300d w123? Not necessarily the flush, etc, I am just trying to decide if it's worth renting a bay with a lift, or just working on jackstands.

funola · #8 06-05-2016, 07:33 PM

The temp switch comes on at 52C 125F IIRC. You could test it in warm water / thermometer and an ohmmeter to make sure it is working. Did you feel the dryer if it was getting warm? If you have the manifold gauge set, why not diy? You can rent a vac pump from Autozone. That's what I just did to charge my 85 300D with R152a Dustoff and it is colder than R134a. Time will tell if it is longer lasting than 134a, which does not last in mine and AC performance gets weaker with time (months). This is with the original non barrier hoses.

Demothen · #9 06-05-2016, 07:40 PM

I didn't realize autozone rented pumps. Awesome!
This was sort of a DIY, there is a local DIY repair place where you can rent a bay hourly, I went there to use their pump, and while I was there I asked the person who was running the place to help me charge the system since I have no real experience.
I will test the temp switch with hot water, that's a good idea. The receiver was not getting warm, at least not 125 degrees warm. We seriously only got a partial 12oz can to flow into the system, it was not pulling down the low side enough to drain the can.

funola · #10 06-05-2016, 07:53 PM

Some Autozones have it some don't. Make sure there is enough compressor oil in the sight glass before you leave the store. You should be able to remove the compressor on jack stands. I can't give you an exact time since the last one I removed was a long time ago. I'd guess 1 to 2 hours at most. A lift would make it easier of course.

leathermang · #11 06-05-2016, 07:53 PM

WEAR GOGGLES....

did you have the refrigerant can in hot water ?

perhaps you could direct wire the fans ?

I sure think it is a two day job....nothing ever just takes the predicted time for me... missing parts, broken stuff.... etc... changing the compressor...

use proper color NYLOG ...which is the correct oil but thickened.... as per the MB ac manual...

Needs to be a two stage pump and leave on as long as your patience will allow.....

Demothen · #12 06-05-2016, 08:52 PM

No hot water. Will try that next time. Though I still don't think the system was building pressure & vacuum right.
Hmm, nylog eh? Don't remember reading about that. I will try to find some.

leathermang · #13 06-05-2016, 09:08 PM

and you say ' pshaw' to the paper manual..... lol
hard to find that kind of stuff on a cd...
you have to be looking for it...

Demothen · #14 06-05-2016, 09:15 PM

CD's? What is this, the 90's? http://www.peachparts.com/shopforum/2155238-post1.html
Though it might not have the entire HVAC stuff, which might very well explain why I hadn't heard of that before.