One suggestion I've received to figure out why my heater blows hot air all the time was to test the air temperature sensor.

The manual says to test with an ohmmeter. What should the reading be?

r

mjk

84 300SD 90.3KMi

It depends on the temperature. Here are the values from the service manual.

Temp Resistance
15C 15.7 KOhms
25C 10.0 KOhms
35C 6.5 KOhms
80C 1.5 KOhms

I would focus my attention on the monovalve connector.

Thanks for the values. I should have done a better job looking in the manual, I guess.

Yes, a sticking monovalve seems to be the culprit. I'll post when I have a bit more time to characterize the problem.

__________________
mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)

Also make sure the foam tube in the dash has not disintegrated.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car