1983 300SD Air Conditioner

[Nuggler0]

I am starting to diagnose problems with my air conditioner. I can't get the compressor to engage. Any thoughts on what to check first? Perhaps there is a thread out here on the subject.

[sixto]

If there's a thread in the archives, you'll find it using the search function.

The ACC is a pretty complex system. I saw your post about the shop manual. The CD set has a diagnostic procedure for the ACC.

Sixto
95 S420
87 300SDL

[BIG MIKE]

Sounds like your system is low on refrigerant. (most likely cause for clutch not engaging) BIG MIKE

[Nuggler0]

What should the low side and high side pressures be on my '83 300SD.

I was able to get the compressor running. Low side pressure was at 13psi. The compressor came on at about 20psi but I'm not sure where the settings should be at.

[engatwork]

Running r12 should give between 30-35 psi lo, 200-250 high these numbers are based on ambient conditions but should be good "ballpark" numbers.

[Nuggler0]

Thanks, Jim. I have r134a in the car. It had been converted prior to my buying it. Would the pressures be the same with R143a?

[engatwork]

Hi side could run up to around 300 psi or so with 134. Not exactly sure about low side but I suspect it should be the same as with r12.

[Nuggler0]

Set the low side at 35psi. The temp is cold but feels like it should be colder even when cruising at 3000 rpm. Got the Service CD for the 126 and it says to check the manual for the proper settings. Anyone know where the specs may be hiding online somewhere?

We're almost there...

[David Carlton]

I saw you were able to get your compressor working. My compressor stopped working. When I eck the electrical conection to the compressor it does not show any juice going to compressor. Any ideas?

[Nuggler0]

You may want to check the thermostat. I didn't check my connection to see if I had juice or not. When I put the gauges on the low side I could see that the pressure was around 13psi. When I got to 20psi the compressor started. I do not know whether the low pressure prevents electrical from getting to the compressor. It would make more sense for there to be a low pressure switch that prevents the clutch on the compressor from engaging.