1985 300D Heater / AC

[darylorr]

I have a 1985 300d Turbo Diesel, and the car's ac has been converted to the new 134. I tunr the air temp control dial to cold and very hot air comes out. I click the ec button to get outside air to flow and I still get very hot air. Its stuck to cook me onthe inside. I do hear the ac compressor turn on but no cold air in ac mode and no cool or cold air at all . On occasion the air will come out all vents hot. if i turn it off then it seems to reset to the 2 outter vents as in the EC mode? Any ideas? Vaccum, electrical ? And any areas I need to check ? - Daryl

[lrg]

Do a search using the word monovalve and you will see a recent thread where someone else had the same problem. It also sounds like your A/C may need some attention but check out the monovalve first.

[GregS]

Most likely you have a bad foam tube behind the glovebox. Pull glovebox, replace foam tube with foam pipe insulation from Home Depot. Make sure you have a tight, leak free seal on both ends. Do this before you touch the monovalve. Its a cheaper fix. Do a search as I've posted about this many times before. Everyone says "monovalve," but the foam tube should be replaced before anything else is touched. And don't "inspect" it, just replace it, since it may have a hole you can't see outright.

GregS
'84 300D, 174k
'90 300CE, 164k

[darylorr]

Ok I tinkered around witht he a wires ect ect . IT works. I however find the foam behind the glove bo as "mushy" Its replaced. Now I have the problem where the enter vents do not open easily. the valve that allows it to open does work, but I have to just slighty tap the vent for it to open. it is hard to see what is wrong beind it, wheather the foam got in there and made the opening hard or did something break? Also I have this wire hanging with an exposed end consisting of 2 little prongs with some sodier on it looks like it might have broke off of an electrical board, is this the sensor for the climate control ? if so where does it plug in. When i found it it was tucked in between the to rubber boots that go to the center vents. - Daryl

[lrg]

The electrical piece you see probably is a temp sensor and it should fit in a hole just below the little air intake vent in the center of the dash that the foam tube goes to. There is a small blower at the other end of the foam tube that sucks air past the sensor so the sensor gets a continual sampling of air temp. GregS is right that these foam tubes are often bad and easy to fix but for the record, this time of year a bad tube tends to make the system cool too much not heat too much. Sun on the dash heats up the air back there and a hole in the tube sucks the hot air into the sensor at the sampling motor. That trips the A/C on but since it doesn't cool behind the dash too well the sensor thinks it's still too hot and leaves the A/C on full blast. On the 124 chassis they fixed that tendancy to over cool by putting the intake on the headliner by the interior light, away from the sun. If you are getting full heat, trust me, it is not from a bad foam tube.

Your vent problem sounds very much like a bad vacuum acuator. These have rubber bladders that dry out over time and start to do funny things. The one that operates the center vents frequently fails and my guess is that yours needs replacing. The good news is the part is not expensive. The bad news is it's a PIA to get to and something that will cost a fortune to pay someone to do. If you want to replace it yourself (it's not hard, just takes a while) do a search and you will find a couple of excellent, detailed descriptions on how to do it. If you don't care that much, others here just prop them open for the summer and shut them for the winter since they only provide cooling. Good luck

[darylorr]

Thanks for the help guys. I took out the glove box again and found that the arm that attached to the center vent was missing a nut . I repleced the nut and bolt and it works.