Another A/C Problem on a W124 300TE

I'm hoping against the worst case scenario here. My 1991 300TE 4matic has 255 k miles on it and I converted to R134a last summer. Everything was good for the summer then.

Two weeks ago, my wife tells me the air isn't working. First time she's checked this summer. I added some R134a on a cool Saturday morning, charging to 175 psig head pressure, which was around 2 1/4 times ambient at the time. The car ran cold for a few days, now it's back to no a/c. Worse yet, the clutch is turning and I'm not getting any cooling!!

I'm going to check pressures this weekend, but I don't know any way to get the clutch to turn with no cooling effect other than a blown compressor. Any other ideas out there???

Please let me know. Thanks.

[ChipJ]

it could be anywhere. If the compressor is coming on but you are again low on freon then your low pressure safety switch is also not working properly. For your sake I hope it isn't the evaporator. You really have to take it to someone with a leak detector, have them add some dye to the system and find out where it is leaking.

I checked the pressures today, and they were low. In fact, the compressor was pulling a slight vacuum and the pressure switch wasn't cutting it out. So I added about 10 oz. of R134a and I'm getting 28 F cooling differential at the vents. Now I gotta find the leak, fix the leak, and replace the bad pressure switch.

The good news is the compressor is still happy and so am I, because that and the evaporator are the two biggest body blows on MB A/C units as far as cost goes. I figure I'll be lucky if I can replace a 124 compressor, including recvr/drier and exp valve for less than $1000, with me doing all of the work.

We're not there yet, so I'm a happy camper.

ttfn

[stevebfl]

The pressure switch is on the high side of the system. A 20% full system would have plenty of pressure to activate the switch and probably would pull a vacuum on the low side due to low charge.

I wouldn't be surprised to see a 1% of charge fill have enough pressure to activate the system.