w115 a/c compressor not working. help! - PeachParts Mercedes-Benz Forum

NC240D76 · #1 06-07-2005, 11:32 PM

The a/c compressor on my 76 240d is not coming on and it is getting warm here.
I jumped the a/c clutch and it engages.
I charged the system and it is full although the pressure is a little low.
The line going back to the firewall gets very cold quickly.
The fuses and the relay on the passenger firewall are both working.
The blower switch works for the defrost and heat settings but the ac switch does not kick the blower up high like it did last summer.
I do seem to have continuity through the ac temp control switch.
The vacuum lines appear to be in the correct place.
I had the console out while replacing interior and carpet but everything went back where I thought I removed it from.
What am I missing? I do not see a pressure switch in the system, when I short the switch on the evaporator, the aux fan on the radiator comes on.
And want the heck is the red wire to the a/c temp control switch? It does not show up on any schematic I have seen.

I have searched but w115 a/c questions have been few and far between, it must be a good system for the most part (or everybody else gave up)

Thanks for the help.

NC240D76 · #2 06-09-2005, 12:03 AM

bump
just hoping for fresh set of eyes to look at this problem for me.

leathermang · #3 06-09-2005, 12:11 AM

Sorry, all my literature is for a 123....

" I do not see a pressure switch in the system, when I short the switch on the evaporator, the aux fan on the radiator comes on.
And want the heck is the red wire to the a/c temp control switch? It does not show up on any schematic I have seen."

Do you mean the switch on the Receiver/Dryer rather than the evaporator?
Do you have two switches on the plumbing at the Receiver/Dryer ?

NC240D76 · #4 06-12-2005, 11:22 PM

I guess the reciever/dryer, the little rascal on the extreme passenger side firewall with the sight glass on the top.
Just one set of wires going to it. No other wires near it.

leathermang · #5 06-12-2005, 11:42 PM

Yes, that critter... usually there are two switches right there... one on top and one on the side.... but the low pressure cut out switch could be located anywhere the refrigerant is...
Start at the compressor and go backwards... is there a relay which is supposed to provide the electricity to the compressor clutch ?
Check for power at that relay...and check to see what sends the control current to the relay...

Palangi · #6 06-12-2005, 11:47 PM

115 A/C is uhhh... wierd. What operates that relay is vacuum, not current.

leathermang · #7 06-12-2005, 11:53 PM

Paul, I am covered... already said I only have 123 literature... just keeping him company until you could post....

Palangi · #8 06-13-2005, 12:04 AM

I remember I looked at the wiring and vacuum diagram for that thing for hours before I finally gave up. On Nellibelle A/C blower worked but the heater fan didn't. I finally just assumed that the blower motor was bad. Eventually figured out how to take out the compressor fuse and set the levers so the A/C fan would blow a little heat.

Ooh that was a brainwarming.... I forgot, there is a fuse for the compressor in a little box on the passenger side of the engine. Follow the 12 volt wire from the compressor back to the little box.

NC240D76 · #9 06-15-2005, 11:22 PM

I think I have checked everything except the "change-over switch which I assume is the pair of sliding switches that changes the temp control from hot to cold and back. I can not figure how to get to the backside of the sliders or to pull the entire unit.
When I pull the forward part of the center console I have access to the a/c manual thermostat but the radio is between me and the temp control area (sliders), if I pull the glove box I can see the end of one or two of the controls but not enough and not well.
Is there any way to slide the entire unit forward so I can get to the wire on the changeover or am I missing something and making this harder than it should be?
I still have not found a switch for low pressure on the a/c lines and I do not see one in the wiring schematic but I did charge the system and the pressure is good.
Both fuses (F21 & F22) on the passenger farewall are good and the a/c interupt relay for the start circuit under the above fuses is working correctly.
Thanks for the help,
Brian

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