a/c headaches
 

1982 300sd, trying to locate the compressor control relay.
woke up this morning and it no longer worked. was fine the night before. the clutch is not engaging. anyone have some input.

thank you flyboy

Jump the low pressure switch connectors on the receiver / dryer with the ignition on and the engine off. If clutch engages then your low on pressure (most likely) or you have a bad switch (very unlikely). That is the easiest first trouble shooting test.

Hmmm
 

Overnight failure.
#1. Check for failed A/C Lock-Out Sensor.
#2. Check for failed A/C Pressure Switch, 2 bar low pressure and 30 bar high pressure binary switch. Located on reciever-drier with 2 spade terminals. Used for compressor cut-out.

#3. Check for failed A/C Evap Temp Sensor.
#4. Check system pressure.

#5. Possible failed Climate Control Unit.
#6. Possible failed A/C Compressor clutch.

Need help from the experts:

First, I replaced my ACC unit. This got my monovalve working and allowed me to use the "Off" button. Finally, no more searing hot air constantly blowing through the vents.

Next, jumped the cutout wires and clutch will now engage. Placed the wires back on the Pressure Switch and low an behold my compressor stayed engaged for about 15 seconds, then cut out.

So, I think I have a bad switch. I have not been able to take readings on the system, so I can't give you high and low side pressure.

Question is, if my switch is bad, am I looking at a complete evacuation in order to replace it?

Thanks for your help!

Good work! Your moving right along.

You may not have a bad switch. At this point you need to monitor your low and high side pressure to move the troubleshooting forward.

Good luck,

Only because I have experts here on the "Shop" to help me.

I'll have to get that reading done I guess.

I also have a leaking power steering pump that is keeping things quite soggy, so I'll also try getting those wires cleaned.

So, if I do find that my switch is bad, is changing it a job that requires a complete system evac?

Thanks Larry!!

If it is the pressure switch ,yes.

I was afraid you were going to say that....

Interesting coincidence....there is a new shop on the way to work....Something like Prestige or Pampered auto...anyways...my wife shows me an ad we got from them in the mail. Addressed directly to me and offering a free AC check on my Mercedes.... :eek:

That was too weird....

They had a 300D in there (it's in the picture of the place on the ad) that is identical to SWMBO's new one !

So, looks like I'm going for a free AC check, after I replace the power steering pump and hose down the engine compartment.