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Old 06-29-2002, 07:35 PM
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Join Date: Dec 2001
Location: Long Island, New York
Posts: 4
Question w124 diesel A/C problem

Here's my problem. I replaced a leaky ac hose on my 1987 300d and decided to switch over to r134. I put 1 can of 134 in and the compressor turned on. I then added the oil, and 1 more can of 134 and the compressor would keep cycling on and off. I had a friend of mine evacuate the system & check the amount of 134 in the system. However, the compressor will no longer come on. I when through the troubleshooting steps from the shop cd rom and checked the voltage on the poles from the Klima relay. When I jumped circuits 5 & 7 the compressor came on, but the air didn't blow cold in the car. I replaced the relay as the manual said, but that didn't work either. A friend of mine at the dealer said I should replace the rec. dryer since the r12 & r134 could possibly gel and clog it up, explaining why I didn't get cold air inside the car. I still don't understand why the compressor isn't coming on though. Any ideas would really help out.
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Old 06-29-2002, 08:21 PM
jbaj007's Avatar
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Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
Make sure you don't still have a leak and your pressure is just too low to activate low pressure switch now. '87 300D should take ~34oz. of R134a. If you're using 12oz. cans (and only two) you're way short, also. Definitely replace receiver/dryer,(system flush would be good) (new expansion valve for 134a is good; although on MB they are probably the same as the R12 valve to be honest). Add correct amount of oil (PAG or ester) (about 4.1 oz. in a flushed system for '87 to "89 MB) and pull a good long vacuum. Charge into the vacuum with the first can (either as liquid or gas) then add second can while checking pressures, then SLOWLY add third can while really keeping an eye on pressures, particularly high side (2.2 to 2.5 times ambient temp. in *F).
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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Old 06-30-2002, 01:24 AM
WRM WRM is offline
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Join Date: Jun 2002
Location: BURBANK CA
Posts: 151
remember you need to drain the old r-12 oil because they don't mix. also you can't put as much r-134 in the system like in a r-12 system.
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