A/C blows hot.
 

Hey folks!

I have a 84' 300DT. Y/D, after work I started the car up and set sail for home. To my suprise the A/C system started to blow hot. It was 93F outside and my thermostat was on 22C. My center vent does not work so i suspect a vacuum issue there. But the temperature control has not been a problem before. Any suggestions to the problem.

Thank you

BTW: This site has saved me lots of time and money and i just want to thank everyone for being so helpfull and knowlegable.

when mine did this it was because of the valve on the passenger side firewall. it is supposed to regulate the flow of engine coolant. it turned out that the terminals were dirty and it was not closing. this should have 12v when the temp is all the way clicked down.

That would be a monovalve. You also need to make sure the compressor is operating and that freon pressures are good.

Was the problem with the center vents pre-existing or did it occur concurrently with the hot air episode?

The centervent issue was preexisting. The compressor was changed recently and the hot air is"heater hot"...

If it's "heater hot," the monovalve is open for some reason. Maybe a bad monovavle, maybe a fuse, maybe a control unit.

I agree with the monovalve. You should check it and make sure that you have 12v across the connectors when you have the temp dial on MIN.

If you have 12V then it is probably the valve insert that has gone bad.
If not, then you probably blew the climate controller or the fuse. The fuse also controls things like the transmission kick down and the reverse lights so if the fuse goes you should notice other things "wrong" with the car.

The CCU can blow due to the Aux water pump drawing too much current and melting the solder. Do a search on CCU fixes to see how to repair it. It is pretty easy, but takes some time and a soldering iron.

To change a bad monovalve insert takes five minutes and the loss of a little coolant. You can get replacement inserts many places including on this site.

It is funny how my BMW uses the same monovalve but as never had an issue in 24 years. Wonder if I just jinxed it...

Thank you so much. I'll look into it...

Check all fuses on the firewall in the engine compartment.