A/C problems, help needed. - PeachParts Mercedes-Benz Forum

BSharp · #1 07-27-2011, 02:38 PM

All right. I am stumped. I could use some help. A little history. I have a 87 190D 2.5.Turbo. When I bought it it had been converted to R134a. The compressor said R134a on it and it had a conversion sticker on the air filter housing. Over the last two summers it is cooled "just enough". The best it would do was 60 F, @ hwy speeds, a/c clutch hard wired and recirc on. New fan clutch, both aux. fans working, heater valve working, vacuum pods replaced. I took some freon out, no better, added a little, no change. So I figured R12 would work better and since I had some, why not. Without knowing what oil was in the system I drained and flushed it. Flushed the cond., evap, lines, drained the compressor. I then put 4-5 oz of ester oil in the system, replaced the dryer and expansion valve as well at the o-rings. I vacuumed the system and added 3 cans (36 oz, calls for 38 oz). Still can only get 55-60 while moving. Here are the specs using an R12 gauge set and a digital contact themometer.

2000 rpm
280 psi high side
30 low side

2000 rpm
156 F cond inlet
142 F cond outlet
112 F cond outlet (water soaked)

116 F evap inlet
65 F evap outlet

The pressure looks ok, there does not seem to be much temp drop across the cond. but I checked my 95 Lightning and it was similar.

Any ideas? Thanks

leathermang · #2 07-27-2011, 03:03 PM

Is your compressor still hard wired on ?

BSharp · #3 07-27-2011, 03:10 PM

Yes, still hard wired on.

leathermang · #4 07-27-2011, 03:29 PM

Was the new expansion valve marked for R12 or R134a ?
Is this an R4 Delco compressor ?
Is there a place the hot water line could be squeezed off... are you sure there is no hot water leakage to the heater core ?
Are you sure the flaps are in the proper places for what your settings are on the dash ?

BSharp · #5 07-27-2011, 03:42 PM

Quote:

Originally Posted by leathermang

Was the new expansion valve marked for R12 or R134a ?
Is this an R4 Delco compressor ?
Is there a place the hot water line could be squeezed off... are you sure there is no hot water leakage to the heater core ?
Are you sure the flaps are in the proper places for what your settings are on the dash ?

I do not think the expansion valve and ant makings. I will look at the box.

No R4, I think Sanyo or Sanden were used.

I can feel the heater lines, they are not hot.

I know the recirc. door is working, and I can move the temp wheel to warm and it get warmer.

leathermang · #6 07-27-2011, 03:45 PM

Is your temp wheel totally maxed out to the cold side in these tests ?

BSharp · #7 07-27-2011, 04:04 PM

Yes it is, and I have tried 2 different CCU's. I have checked for leaves between the cond and rad and there are none. The cond "looks" clean. I think one tale tell sign in the line coming from the evap. it is only 65 F.

leathermang · #8 07-27-2011, 04:23 PM

Ok... sounds like you might need to clean your evap fins ...if you have not already.....

BSharp · #9 07-27-2011, 05:15 PM

I was thinking that but it seems the evap outlet pipe would be cooler

leathermang · #10 07-27-2011, 06:40 PM

You want the evap outlet ( if you are able to measure at the correct place accurately ) to be relatively warm.... having left the cold in (non tech description) the air passing across it at the fins of the evaporator... but in addition to that ... what other parts does your AC have which could be malfunctioning ?
Your car has more parts than my type one AC...but you still have a finite number of things which can go wrong... and I think you are down to choosing the cheapest or most effective things to fix next....
If you had your evap outlet 10 degrees hotter... having transferred that to the air inside you would have 45 at the vent .... I assume it is hot there in DFW during your test.. (LOL) so getting the outlet of the evap closer to ambient than Half... would have to help your inside temperature...

leathermang · #11 07-27-2011, 06:58 PM

But James... what is the problem ? You don't want to commit a significant portion of the rest of the year to becoming an expert in removing and reinstalling the dash on your car ? You perhaps have a LIFE apart from providing DIY instructions for the Forum ?
I think taking the dash apart and putting it back together is listed as a quick 17 hours in the Flat Rate manual.... a rest break from the rest of life's hassles....
LOL

BSharp · #12 07-27-2011, 08:14 PM

Did some more testing. On the way home the best it could do was 65. I used over cleaner to clean the cond. I put the temp probe through the center vent and took a reading directly on the evap. 2000 rpm the best was 58.5 F. I am wondering if I do not have too much oil. The sight gauge will not clear up. Once I shut it off bubbles still slowly go by the sight glass.

leathermang · #13 07-27-2011, 09:41 PM

IF you flushed it...and only added 4-5 oz of oil.... I can not imagine that you have too much oil....
Have you cleaned the fins on your evaporator or not ?
Is the site gauge the only reason you worry about the amount of oil ?