MY 300SD will either freeze you or roast you. There is no modulation of heat or A/C. The blower speed increases or decreases normally but the temperature in A/C mode is 36 degrees which is fine in the summer but on a 75 degree day a little cool, and when the blower slowes down it feels even cooler. Likewise the heat blows hot when called upon but never is tempered.

My manual states there is a 5 second pulse signal (ground side) to the mono valve. Obviously this is not happening. Does that signal generate from the Electronic Switchgear or the Control Head? Anyone else seen this issue? I did an extensive search and have not seen this addressed in the past. Hope I am not duplicating. TIA.

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"Without Fleet The Pride Doesn't Ride"

1983 300SD 609K + still going strong!
1970 Monte Carlo
1994 Ford F150