This is probably an easy one for someone...

I've got a problem with the operation of the heater/defroster system. The car is a 1982 242 turbo. I live in a place that relatively cold, so in the morning when I first take off, I usually have the defroster activated (switch pushed in). It works just fine (warm air blows only out the defroster ducts) until I start driving... specifically, until I start accelerating. At this point warm air also blows out the heater ducts. When I back off the accelerator, the warm air quits blowing out the heater ducts (but still blows out the defroster ducts).

I think that this is a turbo-only problem: It appears that this anomaly occurs when the engine speed is increased, which causes the turbine to spin up and create positive manifold pressure. The positive manifold pressure (somehow) allows the warm air to get to the heater ducts.

Since the switching for the defroster/heater system is vacuum-controlled, I am assuming that I probably have a problem with a seal or a diaphram.

Anybody got any experience with this? Any thoughts?

Thanks.

Julio has it right. I could blow through mine both ways, and fixed it by simply running hot water through it. It's held for 6 months now. Maybe water is a little less caustic than carb cleaner.

A symptom before the fix, was that when you turned off the engine, you could hear a loud hiss from the centre console - air being sucked back into the reservior from the intake manifold through the leaking check valve. When it's working right, after turning off the engine, you should be able to open/close each of the vents (using the pushbuttons) several times before all the vacuum in the reservoir is used up.

Check valve.

Those damned things suck. Or not.
--
Don Foster (near Cape Cod, MA)

Bob & Mitten Head have hit this one on the nose. Just look near the firewall for a vacuum line coming from the intake manifold going into the passanger compartment around the center/drivers side of the firewall. This one way valve some times sticks but most of the time fails. If you find it look at the hoses connected to it. This problem might be a result of a broken hose (usually the one coming from inside the car). Take the valve out. Blow in it both ways and you'll have your answer. If you can blow only on way (engine to passanger compartment) then it is okay. If you can blow in it both ways then try cleaning it with carb/air intake cleaner but keep in mind that your most likely going to need one really soon. A good excuse for a trip to the boneyard. Good Luck!

Sincerely,
--
Julio Meza

1979 264GL B27F 122K

Features Added:

BW55 To M46, Central Locking System, 25mm IPD Front Sway Bar, 81+ Dash W/ Oil & Ambient Temp Gauges In C, Oil Pressure, Volts

Next Project:

+Cruise Control

Les, this is gathered from my sometimes leaky memory from other BBRD posts.

There is a vacuum reservoir for the air duct control motors. It looks like three conjoined spheres and is mounted under the air plenum box.

The manifold vacuum line goes from the engine to that reservoir, and thence to the switch system. There is, IIRC, a check valve in that vacuum line so that the vacuum does not "leak out" back to the engine when manifold vacuum drops. Your symptoms seem like those I would expect if that check valve was not working.

I don't know where that valve is located, perhaps it can be found by following the vacuum line.

Good Luck,

Bob

:>)

Thanks for the info, Bob. Good to hear from you.

Les

I suspect, from experience with other things having to do with the heater, that the check valve is mounted inside the differential housing, or some other convienient place. Sort of common sense suggests that another one could be stuck in some accessable place on the vaccuum line.