rabney72

Hi guys,

I am working on my grandpa's 1991 560 Sel and I am experiencing the weirdest symptoms I have ever seen. (Done over 100 ac jobs never seen this before).

Here's the run down. The ac was gradually blowing hotter (slow leak on freon). It's getting hot enough outside now to matter so I just evacuated the system of all gas, pulled vacuum overnight and filled it up with 3lbs of r12. The vehicle calls for 2.9lbs, so it's essentially full. The compressor kick on and off fine when commanded, the fan motor blows hard etc. The craziness is in the pressure readings --- with the car idling ac off there is approx 100psi of gas in the system equalized across both sides. When I turn the compressor (ac switch inside car) on the low side pumps down below 0psi to about 2in of vacuum and the high side only goes up to about 140psi....this is unbelievable.

Generally with a restriction in the system the low side will pull down like what I'm seeing but at the same time the high side would skyrocket. On the contrary , with a "too open" valve or worn out orifice, there will be less restriction than normal and the high and low side would be close to each other in pressure, In my case say 80psi on the low and 120psi on the high..

So what in the world is going on?? Could the compressor potentially all of a sudden decide to be a black sheep and pull good vacuum but not build pressure??? I don't even think this is possible from a thermodynamics standpoint unless there is something else (like a subsystem) to this ac system..

Now I understand this car has an expansion valve rather than an orifice tube but what other crazy stuff is going on with this system. I see two lines coming off the low side line just outside the firewall by the brake booster and going under the intake cover - not sure what these are or where they are going.

I could just replace the compressor, drier, expansion valve, and condenser but I'm not convinced my problem is within those items...I have the mbusa manual and it sucks , doesn't have much detail and what it does show is just basic diagrams of an automotive ac system .

All help , input , and questions would be appreciated.

Thanks
Robert

tombutler

Hi, can you call me when you have a few minutes? I just need a little info on replacing an AC compressor.

310-709-2488

Thanks, Tom Butler