It's getting hot, a/c not working

[fpilot]

Hi everyone! I have a 1986 560sl and recently was told the compressor was no good since my car was not blowing cold air. Air was coming out but not cold. Ok, so had the compressor replaced along with everything else that goes with it. Still no cold air. The compressor would not kick in, so bought a new relay switch since we saw the old one was burnt. That had not corrected the problem. Saw the switch on the dryer (thermostat switch, I think) had to be grounded to kick on the compressor (if I got that right). Any suggestions? It is getting hot already here in Texas.

Thank you kindly!

[SunGuy]

Did you change the monovalve with all the other parts?

Bob

[dpetryk]

Did you ever get the compressor to engage? If not, then how were you able to get the freon in the system? Did you replace the clutch magnet? They fail and prevent the compressor from engaging. Who did the compressor replacement? Did they evacuate the system? The wires on the switch at the dryer are not to be grounded they should be tied together. IF you did ground these wires its possible that something else in the circuit is now damaged. That switch senses system pressure and if there is no freon in the system it prevents the compressor from running and destroying itself from lack of lubrication. Compressor running + No freon = no lube = compressor AFU.

Give us more details to work with.

[Alkraut]

With the temp dial on AC Max and the up/down button pushed the compressor should engage. While running, lift hood and check the large line on the driver's side upper fender to see if it is ice cold. That's a quick indication if the compressor and refrigerant is working.

[fpilot]

Sunguy - Monovalve is that the same as expansion valve?

We have no power to the compressor. Also, the lights on the dash are very dim. Could that be a connection to why there is no power?

Thank you all!

[fpilot]

The compressor came on when grounded the wire switch that is on the dryer.

[Alkraut]

The monovalve is the hot water (coolant) valve for the heater. It is not part of the AC system, but rather part of the heater system. The expansion valve is in the AC system. Both are part of the climate control. If the monovalve stays open during the AC cycle, you can get heat and AC at same time and air will not blow cold. I'm sure that Sunguy mentioned it because a malfunctioning monovalve is a common problem and could cause one to think the AC is not working. Happened to me.

[fpilot]

Thank you on the monovalve explanation. I just do not have power to the a/c compressor. It is maddening.

Thanks.

[JFawcett]

I would check the CCU....mine was doing weird things (compressor came on, but no blower - and air distribution wasn't working very well). Besides the CCU HAS to control more things than just the heat/AC - anything with that many wires going to it must control NASA and NORAD.
As the control unit ages, the solder joints break and things just quit working.... get a re-built one from Benz World for $135....unless you are good with a soldering iron to remelt the pathways on the unit.
Eitherway, you can eliminate one more thing.....hate to throw parts at a problem, but there are just too many things that CAN be intermittant on the CCU to not replace.

[Roncallo]

Originally Posted by fpilot

The compressor came on when grounded the wire switch that is on the dryer.

If I recall correctly there are two switches on the dryer and I belive one is a low pressure cut out and one is a high pressure cut out. If your pressures are in normal operating range your compressor should run. The low pressure cutout will typically keep the compressor from starting in real cold weather when line pressures are so low there is a chance of sucking liquid into the compressor. Like wise it will also not allow the compressor to run if the charge is too low.

The high pressure is an over pressure protection that should only stop the compressor when pressure gets too high like over 400PSI.

It is possible that one of these switches is bad or something in the circuitry going to them. It is also most likely that this was the problem all along, and you never needed a compressore or any of the other stuff you got.

God Luck
John Roncallo

[Roncallo]

Originally Posted by fpilot

Sunguy - Monovalve is that the same as expansion valve?

We have no power to the compressor. Also, the lights on the dash are very dim. Could that be a connection to why there is no power?

Thank you all!

Do the lights on the dash get dim only when trying to run AC or all the time. You are aware of the dimmer swich in the instrument cluster. One of the little buttons on the lower edge of the cluster just like the trip odometer and clock set buttons.

John Roncallo

[jbaj007]

When you say "ground", if you are using a jumper on the wires that go to this switch, AND you have between 30 psi to 450 psi static pressure in your system AND then the compressor engages;.....you have a bad switch.