I recall reading somewhere that, once the engine warms up, all of the air intakes and hoses and such get warm too, so that, especially if the car has been sitting in the sun, the climate control will blow warm to hot air in EC mode. I have found that, on a sunny day, even if the air temp is low, the car gets warm enough so that a/c is necessary.

However, if you are talking about genuine HOT air, then something is amiss with the mono valve. If the mono valve doesn't get a reliable 12 Volts, it will not stay closed (0 Volts = mono valve open). You can experiment by running an external wire that will allow you to put 12 Volts on the mono valve by turning a switch. If you can turn the hot air on and off by cycling that switch, then the mono valve is working. The problem is then the connector, the wiring to the ACC, or the ACC itself.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970