I have a 1985 300D with a malfunctioning climate control system. The blower will only come on before engine start when the ignition key is in the on position. After engine start the blower will almost always shut off (while controls are still requesting the blower to run). If the blower continues to run after engine start the heater will blow warm air as long as the engine remains at low RPM. Once the engine RPM increases above 2000 RPM the heater will blow cold air. What is the problem?

Thanks

Pilot

I think that you have two problems. The first is the ignition switch. It is not very expensive and pretty easy to replace.

The second problem is not so easily diagnosed, but I expect that you have a vacuum problem of some sort under the dash, but there are several things that could be causing this. I would start by pulling the glove box and ensure that the foam hose is in place that goes from the horizontal pipe behind the glove box to the temp sensor in the center top of the dash. I would also make sure that the monovalve is not flooded. These are not likely for your symptoms but very quick and easy to check.

I've never had to mess with the vacuum pods on your model, so I don't know exactly what to tell you on that except to check the lines near the oil filter that go through the firewall. That is where the vac source is applied to the underdash climate control.

Good luck,

I think the mono valve has a torn diaphram. With the increase in rpm you get a increase in water flow through the valve. With a torn diaphram the valve will not work properly. The valve is easy to rebuild. Replaced mine on a 1984 300D.

To get the blower to work with the engine running just barely turn the key towards the off position and it will come one before the engine shuts off. It will be a very slight nudge to the left and it will come on. I had the same problem in my SDL, it was the electronic portion of the key switch. Is what's happening is the spring inside is worn and not pushing the key fully back after engaging the starter. On these cars they cut off all power so the starter has more for starting.

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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Monovalve and key switch

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Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

I appreciate all the suggestions, my wife and I will start on the suggestions soon. It appears that it is protocal to list the equipment that own's you?

Pilot

M/B 300D
AC CA
JD 3020
1952 Bristol Bus
BE-18
RC-3
CE-140A
260Z
1970 C-10

All the above are used and not in cherry condition but highly prized.