A/C Question for LarryBible - PeachParts Mercedes-Benz Forum

moparmike · #1 05-17-2003, 06:36 PM

I have used the search feature on here, but to no avail. I have a 1983 380 SEL that was converted to 134, and it no longer works.

There are 2 possible causes, one of which I know, the other I am hoping to find here:

1. Bad control cluster, but had that replaced in January (no heat sucks on a snowy day). A/C worked when I bought the car, in Sept. 02. Did not test to see if A/C worked afterwards myself. Was worried more about heat at the time :-).

2. Symptoms:

Low side pressure reading is 87-90 psi. Cant take high reading, dont have proper equipment (quick connect wont fit on high side).
Can turn compressor manually, but wont under power.
Was told by MB Specialist to 'short' the compressor leads on the tank on driver side (connector with pigtails). Did nothing.
Economy guage and Tach dip when A/C turned on, but just normal air.

My recharge kit says that 45psi is max for the 134 system. What could possibly be the problem?

Thanks LarryBible in advance (or others with solutions

)

#2 05-18-2003, 10:07 AM

With engine off, carefully jump 12 Volts directly to the clutch and see if it clicks. It is a loud click so you won't miss it if the clutch is working.

If it clicks, then you need follow the circuit back from there. You really need a wiring diagram, but you might be able to trace the wires. Make sure you are jumping the correct sensor. On your particular model I don't know which one it is.

If it does not click you have a bad clutch.

If your gauge is accurate, you most likely have enough refrigerant to engage the low pressure switch, but you REALLY need a manifold set to monitor high and low side once you have the clutch kicking in.

Good luck,

stevebfl · #3 05-18-2003, 06:08 PM

The discrepency between the recommended pressure and your pressure is that you haven't turned yours on. The pressures they recommended were on a running system.

moparmike · #4 05-22-2003, 01:16 AM

Ok, got compressor running w/ direct 12 volt. Havent traced the wires yet, and it cools with direct power (after I charged it. It read ZERO psi when it was running).

Any ideas of what electrical problem it might be?

Thanks,

Mike Richards · #5 05-22-2003, 05:00 AM

I'm confused as to how the system could be cooling with 0 PSI? Perhaps a more enlightened soul will clear this up?

moparmike · #6 05-22-2003, 05:54 AM

and ran direct current to the compressor. It was reading 0-psi before I charged it. Sorry 'bout that.

BobK · #7 05-22-2003, 06:52 AM

Actually it could cool with zero psi on the suction side. Remember that is gauge, not absolute pressure. So it really would be 14.7 pounds of pressure. In other words, there still would be some freon there. With an undercharged system and reving the engine, it is quite possible to see the low side presure drop to zero, but most manifold gauges on the low side go down to 30" vacumn. Biggest problem would be icing the evaporator at that low pressure. That's why they have a low-pressure cutout switch in the system.