The a/c on my '81 300TDt has a strange (to me) problem. I drive the car every day to work and around town maybe 60 miles a day and the a/c works fine. About three months ago I took a trip of about 350 miles and just over half way the a/c stopped working, I though it had gone out but the next day it was working again and has been fine up until Friday. I took another road trip and about 200 miles from home- - same problem no cooling. After sitting for two days it is cooling again but I need to find the problem. The system was converted to r134a by the previous owner and I don't know the quality of the job that was done, but it has cooled pretty well in the year I have had it--only problem is on an extended trip on a hot day. If anyone has any idea of the problem it would be really appreciated.
Thanks
Jeff

1981 300TDt -- 207,000mi

I think you should be more specific on your Q.
When you say AC works I presume all is fine but when you say it does not work-- Do you mean that you get air from the vents but not cold. Does your vents behave properly. I mean does all air come from front vent or nothing comes from front vent. Do yoy hear the blower motor or no. Please be specific and we can help you.

For now do this.
On the receiver dryer there is a pressure switch with two spade connections on it, gently pull them out one by one and clean the contacts and make sure to put them in same place.
Second trace those wires further down and you will find another connection. Most of the times a bad connection here gives an on/off kind of behaviour to AC. Clean them nicely and reattach them.
On the AC compressor there is a set of wire, make sure they are not loose and well connected.

Does you Auxillary fan come on?


Hope this helps.
MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Maybe you're just low on freon? The switch that MVK mentions is the freon pressure switch that switches the compressor off when the system is low on freon.

Next time it doesn't cool, try looking at the compressor to see if it's running. If it isn't, jump the switch and see if it works then. If it does then maybe you're low on freon.

The cooling ability of the W123's A/C amazes me when it's fully charged! The air coming out of the vents is like 30F!

__________________
2008 BMW 335i Coupe

When it stops cooling on a long trip, try switching to the economy position on the pushbuttons. Wait five minutes, then switch the a/c back on. If it cools, most likely your evaporator has frozen up. It's too cold, so the condensation removed from the air flowing through the car freezes on the evaporator rather than stays liquid and drains out the bottom of the car. This behavior only happens on long trips for two reasons. That's the only time you operate the car for a long enough time to coat the evaporator with ice and 2) the a/c can cool better on the highway, so that's the only time the evaporator is likely to be cold enough to actually freeze the condensate.

Your car has an evaporator temperature sensor which is supposed to cycle the compressor off when the evaporator gets too cold. It may be defective, or the copper tube it uses to sense evaporator temperature may not be in contact with the evaporator.