Hey Guys,
I'm back with another problem. Everytime I turn my car on (no matter what the outside or engine temperature is), I get intense heat from the air vents for several minutes (like 10 minutes), then it goes back to normal. Well, I don't know if it's quite normal because then when I want heat later on, it's not that strong. Any ideas what this could be? I really don't know too much about the climate control system in this car but I have an odd feeling that it's some kind of valve (not something electrical), but you guys probably know better than I do. Thanks for the input.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

Replace the monovalve...buy the repair insert from the dealer (about $25 to$40, dependingn on dealer). The monovalve is located on the firewall in the engine compartment near the battery, with coolant hozes and electric wire attached. Takes about 15 min. to fix. Disconnect battery before you do it to avoid frying/shorting anything. The monovalve controls the flow of coolant to the heater core, depending on signal from climate control unit..when it fails, it stays open allowing hot coolant to circulate to heater.

But the hot air stops, and the heater efficiency actually goes down later on. Could it still be the mono-valve? Thanks. If you still think it is, I'll order it tomorrow.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

Alex-
You might check the aux. water pump located in the front right side (passenger side) near the head light. It is a little servo motor about 6 inches long, about as big as your fist. Its held in a rubber grommet. I replaced mine a week ago because it had frozen up and actually shorted out the push button unit. I had to replace the push button unit too.

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Ed
1985 300D w/ 196,000 miles

Alex,

I don't understand the function of the mono-valve but it does mess up the control of heated air. My car was having irregular heat problems.....sometimes warm, sometimes cold, etc. I found the mono-valve was torn. When fixed, all was well.

Apparently many of our older Benzs have a bad mono-valve so you are probably on good footing to change it out on principal, and maybe that'll do the trick with your peculiar heat problem.

FastLane has them. Couple of days max to receive.

Nic
'85 300CD @ 143k miles

I'll try the monovalve fix first (because it's cheaper) and then if that doesn't work, I'll look into Ed's aux. pump and push button idea. Thanks for the input!

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

I was having the same problem in my '82. I replaced the mono valve and it's been fine for two years now.

This one also sounds like it could be a problem with the in-car temperature sensor. It's under that little grille in the center of the dash. A tube runs from the sensor housing down to the blower motor, under the passenger side of the dash. The idea is to constantly draw interior air over the sensor to insure it has an accurate reading. Part of the tube is made of foam and is well known to disintigrate over time.

Test your air draw in this manner: Set the blower to high speed. Check for an air draw into the little grille. Either use a match - blow it out and see if the smoke is drawn in - or see if you can detect a draw using tissue paper.

To repair, remove the glove box. This involves removing the nine or so pop rivets. Pry the heads out, then the body. Then just pull the whole thing right out. A plastic tube arcs up from the right side, over the top of the glove box. Then it turns to foam as it approaches the temp. sensor. If the foam is nasty and deteriorated, clean it up. Replace with whatever is handy. I used a short section of rubber tubing and some duct tape. Worked like a champ for years...