Only hot on the freeway
 

I hardly don't dare to ask...I did a search, a long one. I thought my climate control was not working; no heat when I'm driving in the city, motor blows, but on the freeway when I'm going 80mph for an hour it blows hot. Will a mono-valve repair kit solve my problem?

1978 300CD

Thanks

I'm not familiar with the 1978 300CD, but I thought it had the servo system?, so it wouldn't have a monovalve? My EPC doesn't show any for that year, The EPC shows monovalve 1981 +, as I interpret it. (But I've been wrong lots of times; just ask my wife. ;)

My 79 300CD did the same, check the connector at the servor, also check the circ pump because at low rpm you won't get enough heat if that little pump isn't working. Newer versions of the pump are also better built to resist corrosion and have better seals.

What is the best way to test the circulation pump?

Thanks.

While driving today I was playing with the climate control and it became warm going 40 mph. I tried it many times before and it would never get warm or hot. Don't know yet if the termo is working it seemed that it was at a constant temperature. Will do some tests tomorrow with a thermometer in my car.

Yesterday fixt my odometer and now the heater is working to, happy holidays!

Hook a 12V power source to it and you should be able to hear it or feel it running.

If you are getting heat without explanation your servo could be the problem, but certainly clean up the connectors to it first. If it worked after you fix the speedo maybe there is a loose wire or fuse? tough to say!:confused:

We all are assuming that your engine temperature is up where it should be, right?

If you spilt the servo apart you should be able to activate it by changing the temperature settings and see if the servo moves, you may be able to hear it move before taking it apart, your choice. I always like to see how things work so I took mine apart, the inside of that thing is a crazy little gizmo.:eek: