a/c compressor not kicking in
 

I have an 87 300TD and blower works as do the proper climate control setting but the compressor is not kicking in.

So far I have replaced the OVP and Klima and checked the strip fuse along with all the other fuses which are good. I have also replaced the climate control unit itself which what I believe to be a good one.

Any thoughts on what else it may be? I do not have 12 volts at the pressure switch. So when I bypass the pressure switch the compressor still does not kick on.

My first question would be.... "Are you sure there is refrigerant in the system?" The compressor should turn on unless the electromagnet is burned out. Also, can you turn the compressor clutch by hand fairly easily? :book:

Bad alternator will hurt you. So will a Speed Sensor. CCU could be bad also.

I have a thread on here "SDL + A/C = No Go" or something to that tune, there is lots of info there.

The '87 should have a low pressure cutout, and a high pressure cutout. Both switches are on the filter/dryer.

The tach is not working up to par. It seems to register half the value. Maybe the speed sensor is bad.

Am I right in saying one wire to the pressure switch should have ground. I was thinking it should have 12 volts but I think that was wrong.

So I do have ground at one wire at the pressure switch.

What should the three wires that plug to the compressor register? One 12v, one ground and one????

There are 2 switches on the receiver/drier
 

There are 2 switches on the receiver/drier......the one on top is the pressure switch, and it must have power....because the power passes thru that switch to the AC clutch....safety thing.....(I have my AC clutch disabled by removing one of the wires here)

The other a little lower down is a temperature switch that operates the auxiliary fan.....

The power to the pressure switch/AC compressor clutch.....comes from a relay/contactor just in front of the power brake diagphragm.....

The relay/contactor receives it's electrical input from the temperature wheel......

This is how the '85 300D AC works.....I didn't notice that you had an '87 until after I had typed and posted this....

SB

It's probably the electrical connector at the compressor.
Try jumping 12v directly to the compressor.

It has three wires going to it. I am not sure which terminals to jump? If it had two I am sure it would not matter if power and ground were switched.

I think they work the same.....
 

I don't have a Service Manual for heating and AC in a W124.....but I looked at a parts list......they probably work somewhat similarly......if you don't have 12V at the pressure switch on the Receiver/Drier......your AC clutch will not engage......

The purpose if that pressure switch is to cut out the compressor if the refrigerant discharge head pressure gets too high.......

My car has a rather large relay under a cover just in front of the power brake booster.....under that cover is a black plastic relay with "Siemens Klima" printed on it.....the power that goes thru the HP cutout switch to the AC compressor clutch comes from the relay....when it is energized by the Klima Control/temperature wheel....

SB

I believe that the pressure switch will cut out with the pressure too high or too low. Check for 12v at the switch, if 12v then check the other side of the switch. You should be able to short across either switch to check operation, one will turn the fan on (via the speed resistor) and the other switch should engage the compressor clutch.

I have no power at the pressure switch and jumping the switch does not engage the compressor.

You can do one of a couple of things.....
 

Have you located the relay that I spoke about....that supplies power to the pressure switch "when energized" ??

You could run a wire from the positive terminal of your battery to the pressure switch......one of the leads goes directly to the compressor clutch.....and if the clutch engages....you will know that all is good from that point.....

SB

I do not have the ice cube relays. I have just a klima and an ovp. I also have three wires going to my compressor instead of two. I just want to be sure before I jump things. I do not know if I am suppose to have 12v or ground at the pressure switch. From reading Hitman's post it looks like ground from the pbu engages the clutch. I think I will do some jumping from the klima and see what happens.

Ok, with the pressure switch bypassed I have ground at terminal 10 for the Klima so I assume my pbu is ok. I have no ground or 12v at any of the three terminals of the a/c compressor.

If I jump terminal 7 and 5 for the Klima I get 12v at one of the three wires that attach to the compressor. How do I get one more ground at the compressor. I assume the two wires aside from the 12v wire are for ground from two sources to turn it on?

Is there other terminals I can jump for the Klima that will give me ground at one of the other wires at the compressor?

Sorry, I don't have the book.....
 

Sorry I only have a Service Manual for W123 Climate Control......so have no access to am electrical schematic for your car......

SB