Trying to help a friend long distance with new 560 SEL. It was changed to R134 by owner; did not work when friend purchased. Friend has done this:

Replaced compressor with Denso.
Replaced all hoses.
Flushed entire system
Replaced expansion joint.
Replaced accumulator (dryer bottle)
Recharged with R134a. Apparently no leak.

Did not cool. At one time temp measured 50F while charging but later only 80F at 80F ambient temps. Had very high high-pressure side per gauges and compressor continually cycled on/off. So he decided to go back to R12.

Replaced Schrader valves.
Flushed system.
Replaced accumulator again.
Drained compressor and put in 4 oz mineral.
Put 3 oz mineral oil in low pressure hose
Charged with 42 oz R12.
Result - not cooling (80F again) and low side pressure measured in spec (think he said 50 lbs) but high side too high at 300. He said high pressure measured too high after only one 14oz can of R12 installed (not sure what)

What to do?
Could condensor be clogged and cause excessive high pressure
Could fan clutch be bad and not putting through enough air
Switch out climate control - maybe original bad
Jump the compressor - how to do - if the compressor is not coming on though, how could there be 300 lbs per gauges

As a diesel guy and with little knowledge of AC, I am over my head.

Any comment welcome.

Thx.

I always LOL when people immediately think the refrigerant is the problem. These Gen II 126 cars will blow frosty cold with 134a. $4.88/can vs $30-50/can. It's your call. The performance will be roughly the same due to the multi-circuit condenser and upgraded aux fans.

I see nothing said about pulling a deep vacuum on the system before charging. If that step was skipped there's water in the system and the expansion valve is frozen. What kind of flush was done, did the flushing solvent get blown out with compressed air?

Even the R12 charge was wrong. Densos have a sump, all the oil goes in the compressor on a clean system. They will circulate oil as necessary. Putting oil in the hoses is for R4's or for replacing components without flushing. Factory charge on R12 is 46.4 oz (2.9 pounds) not 42 oz. So even there he's undercharged with ridiculously high pressures.

What brand was the expansion valve? Was it the ACM/Egelhof brand and the correct size? There are 2 sizes, 18000BTU and 24000BTU, the latter is the correct size and the one stocked by most parts houses. Be aware that new expansion valves are drilled for R134a, using R12 with them can result in high head pressure and reduced system capacity (R12 has a larger molecule and different vapor pressure than R134a).

1989 should have the dual Aux fans in front of the condenser. They should be running at anything over 225PSI. If the fan clutch is dead and they aren't running, the head pressure will skyrocket.

Sometimes it's worth it realize one's own limitations and to pay a shop to do the work.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Yep. Deep vac was done.

The charge was 46 or 47 oz. I changed it from 42 later so you must have seen an earlier version of my post.

He used commercial flushing agent and blew it out afterwards with compressed air.

Good question about the expansion valve. I will ask him.

The aux fans are running; I think he hotwired them to make them run all the time. I suggested he use a rolled up newspaper to test the viscous fan clutch but have no feedback yet. Mine lasted 250,000 miles so I would be surprised if his is bad.

Assume there was nothing wrong with splitting the insert of the mineral, just not needed.

Thanks for the response. Will forward it to him.

PS - you will note that he followed all the same procedure using R132a (before going to R12) - deep vac, new expansion valve, etc. - everything. And it did not blow cold. Then he decided to change the Schraders and go to R12. I also have recommended that he find an AC expert now and get help before he spends more money - he is talking about buying and installing a new condensor now thinking that it might be stopped up.

And what would cause the high pressures with both R123a and R12? This was a problem common to both attempts.

Correction - his pressures were 42 and 340.


If I understand this correctly, he placed two 20lb bags on ice on the condensor and immediately got lower temps - about 52F. So he thinks the condensor is blocked and has ordered a new one. May be getting there.

Apparently the problem is resolved. It was the viscous fan clutch. He tested it with a piece of cardboard and it completely stopped. Replaced it yesterday and instantly began to get 52F idling at high fan speed (I thought you were supposed to test at low fan speed) with pressures at 39F and 225F. While I know that is not perfect, it looks pretty close. I suspect he will get cooler temps from the center vent when the car is rolling.

Interesting aspect - says his condensor is painted black and he read that it would be 15% more efficient if he removed all the paint? What??? Assume in 1989 the MB engineers painted it black on purpose and designed around the inefficiency.

Sounds like his Aux fans aren't running. Even if the viscous fan were totally dead, the Aux fans should have moved enough air to keep the pressures down.

Proper charging is ALWAYS done at full load with the fan on high (all windows down, max cold, max fan, in the sun if possible). MB has a really stupid way they perform "tests" on their system that differ greatly from the way the rest of the world works. If he charged properly, he should be 30-32˚ below whatever the ambient temperature is with the fan on high at the center vent at idle. If it's 85 outside, that would be 53-55 at the center vent. Once moving and the system has a chance to pull down the cabin, the temp will drop and the fan will ramp down.

The black paint is there to help the condenser radiate heat. The same thing applies to heatsinks for electronics. Black anodized parts have a higher heat rejection capacity than their bare aluminum counterparts, even if the exact same casting.

Sounds like your friend is an "armchair expert" and well versed in the garbage read about on the Internet from other "armchair experts".

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

You should listen to every single word from disel300, with his instructions i got 41F blowing from the center vents after 3 years of struggling in Houston heat with 70F blowing from the vents, and 55F after 8PM, i flushed with acetone, shop dry air, blow everything out, new seals, new expansion valve, switches, dryer.
yesterday it was 95F outside and my AC was blowing 41F at idle.
Thank you again without you that wouldn't be possible

Diesel300 - thanks for that. You are a wealth of information.