PeachParts Mercedes-Benz Forum - View Single Post - A/C periodically blows hot, and I do mean HOT

lrg · #5 05-15-2003, 01:13 PM

While your foam duct (tube) for the temp. sensor may need replacing, I doubt that is what is causing your sudden heat problem. On hot, sunny days the dash gets hot and if anything a leaky duct will cause the sensor to read a hot temp and turn the A/C up, not the heat up. Also, if it were a simple vacuum pod problem I doubt you'd be getting anything more than ambient air temp from the outside. If you are getting full on hot you likely have an electrical problem that is opening the monovalve and heating the heater matrix. The next time this happens try spinning the temp setting to full cold and see if it makes any difference. Also, on a separate ocassion try pulling the plug on the monovalve (I'm, 99% sure that unplugged/unenergized the valve is closed) and see if when the system goes into unwanted full heat mode if it gets as hot. If you want to get fancy you could rig a bulb to the monovalve plug and observe when it gets turned on. If the sudden heat problem goes away with the monovalve unplugged then it is definitely an electrical/electronic problem.
If so you likely have either a bad temp sensor or bad climate contol unit. Both are relatively easy to replace. If it's the CCU look for a rebuilt unit, they're far cheaper than a new one. Good luck.