85 300D is stuck at full heat-is the monovalve or "flap" or what stuck? Fuse 14 blows over and over and I can't find the short.

No heat modulation

In order to get rid of heat I was thinking of bypassing my heater core for the summer.

I just want to make sure its not one of those Flaps that is stuck.

Is this condition (Full heat) caused by monovolave or flap setting or other?

You most likely have a hole in the mono-valve diaphragm. You need a mono-valve rebuild kit. $46 for the rebuild kit. 10 minute job.

You can inspect the mono-valve by unscrewing the 4 little screws and pulling the assembly out. Probably have a tear in the rubber. You'll lose a bit of coolant doing this so find a spot other than your new driveway that was just installed two weeks ago.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

The monovalve must have power to remain closed. With fuse 14 blown, the monovalve will open to the full heat position.

That should be effective. Plugging a heater hose might be easier.

That's not your primary problem.

A torn monovalve diaphragm will typically cause the heater to not work, especially at higher engine rpm's.

Check for voltage across the monovalve. As stated before, the monovalve needs 12v to stay closed. The valve should have 12v constantly on one wire and use the other wire to complete the circuit to ground. I had a bad wire to mine. I had 12v into the valve, but the line from the valve to ground was bad. I had to resolder it in the CCU...

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If fuse 14 is blown, the isn't going to be any voltage to check!!! No need to even get the voltmeter out of the toolbox.

Thanks everyone. This is truly a 24/7 hotline unparalleled in Internet History. I will do my best to provide ansers to other's problems, but i am more of a builder and restorer and a lousy troubleshooter.

I solved it tonight the Monovalve was stuck!

My ohms reading was correct and at spec. I had read my DVM incorrectly at .005 ohms vice 5 ohms. I opened up the monovavlve and practically had to use a prybar to get it out! The rubber cup was fresh because i replaced it 2 years ago.

I cycled it a few times with a 12 V power supply.

Then I put it back in. My AC came to life!