Working on my friends 400E again. This time A/C compressor clutch is not engaging. Fuse is OK. That is as far as I have gone. Not sure if the R-12 is up to snuff. Would low feon prevent the Compressor from running? What are the next logical steps? Unfortunately I am working on this car away from my shop and tools so this will have to be kept simple. Thanks for any and all input.
Are you able to read the fault codes? If so it would be interesting to know if you are getting a code 6 on PIN 8 - which is "AC compressor clutch blocked". The most common reason it is blocked is that it is unable to complete a test that the engine RPM and the compressor RPM are about the same. The main reasons it can not confirm they are the same is if the serpentive belt is slipping or if it is not getting one of the RPM signals. If it is not getting both signals it can't complete the test and the compressor is blocked and you get the code. If it's missing one of the signals it's probably the compressor RPM signal which comes off a sensor on the back of the compressor, which sometimes fails just because the wire is too short when the motor mounts sag a bit. There's also a high/low pressure switch behind the left headlight which you can bridge to make sure it's not the problem. I might start by giving it 12 volts off the fuse box just to make sure it works. If so you've got an electrical problem and not a problem in the compressor.
probably low r-134, if its a 92 r-12 maybe. Check pressure, hate to say it the 124's have bad units inside the dash. Big money fix. I didnt have the money and used heavy duty A/C leak seal kit and have been holding pressure for 6 months now good thing cause its been 85-95 where I live all summer. If its not low pressure the pressure sensor on the deal behind the drivers side headlight may have gone bad. normally only 2 things.
My 92 400E is original 134. You actually can check the pressure with a recharge kit with a gauge. But the compressor has to be on to get a valid reading. But you can bridge the hi/low pressure switch and if it doesn't come on pressure is not the problem. Doesn't hurt anything to do it for just a few seconds.
No klima relay, it's controlled in the base module/N16, which is located in the black box where the battery would be. Base module is very expensive but fortunately doesn't seem to be a problem very often. It does have some fuses in the top of it so you might check those just to make sure.
Sorry for the delay in responding. Still haven't found the problem. A/C clutch dose not engage. Checked the wire to sensor at rear of Compressor. It is not tight so assume OK. Jumped the Hi and Low switches. No help. Replaced the 16 amp fuse, no help. Checked the 4 10 amp fuses in the module, all are OK. There is pressure in the system, but I do not have my gauges to know how much.
Anything else before I send my friend to a dealer? Thanks for alll the input.
If the compressor doesn't come-on at all, you might want to have the evaporator sensor checked, it's under the dash.
If the compressor comes-on for a few seconds then turns off, you might want to check the sensor behind the compressor. Freon has to be discharged, and you have to pulldown the compressor. The sensor held tighly by a clip, it's not easy to remove.
Anything else before I send my friend to a dealer? Thanks for alll the input.
It sounds like you have not yet done what I would say are the two most important tests - checking pin 8 for fault codes and running a 12 volt wire from the fuse box to the compressor, to see if you have an electrical problem or a compressor clutch problem.
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