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Old 06-20-2009, 09:52   #1 (permalink)
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MAX AC won't stay MAX

'89 Grand Marquis. Long story short, I broke the heater valve (right side of engine) trying to pull the heater hose out of the way to top up tranny fluid. This resulted in an open heater hose and a nice spray of immensely hot water! Didn't get any on me, though, somehow.

Got the new valve, installed it, it works. Valve has a 2-pipe vacuum connection and a 2-wire electrical connection. Temperature control inside works, I get warm air when I ask for it.

New problem is that the climate control system loses vacuum under engine load and the baffle that sets recirculate for MAX AC falls back to outside air until I come off the throttle long enough to get vacuum back in and it returns to recirculate, just for a few seconds. Air stays in the dash vents, although it seems weaker during the problem behavior. Sounds like a check valve has failed, but I don't know any component locations. System was perfect before I broke the heater valve. I don't know how that could be related to the heater valve, but when the hose broke I may have yanked or bumped something somewhere. The 2 vacuum pipes to the heater valve appear to be OK, no visible breaks or cracks.

Clues, suggestions?

Edit: driving around today I'm not getting warm air when I turn it up. That may just be because the air temp is higher than the car's climate range, since it's in the 90's, or it may be that I was mistaken about the valve working the other day. Don't know for sure. Right now I don't seem to get warm air when I set the temp all the way up, though.

I HATE climate control in cars. Anything too small for 50 or 100 people doesn't need "climate control." Just give me a plain ol' heater valve and let me dial what I want!!!! Besides, nobody in Michigan designing these things has a clue about Florida heat and humidity.

EDIT #2: Temperature control works, verified tonight. Setting temp high gives heated air at the vents.

I did find one broken vacuum line, comes from a vacuum solenoid on the fender, repaired, no change in behavior. Still get the recirculate dies on low vacuum.

Last edited by wfooshee; 06-20-2009 at 12:03. Reason: Add'l info
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Old 06-21-2009, 10:54   #2 (permalink)
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Re: MAX AC won't stay MAX

It has to be a vacuum leak, a check valve can also do that. You could have broken another vacuum line with all the movement you had to do. It also could just be coincidental and the leak started somewhere else. You''re on the right track by looking for a vacuum problem.
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Old 06-22-2009, 15:29   #3 (permalink)
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Re: MAX AC won't stay MAX

The vacuum line for the recirc motor is white & small. (The one for the e-brake release is much larger.) Find it under the dash near the control panel & follow it to the motor. But the leak could be almost anywhere, so listen for a gentle hiss.
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Old 10-06-2009, 20:51   #4 (permalink)
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Re: MAX AC won't stay MAX

Sorry to dredge up the old thread, but it's MY old thread, so there!

Found the problem, not a leak at all. That device I installed in the heater hose is defective, and it's not a heater valve at all, it's a sensor! Its only purpose in life is to prevent the blower from operating, and the floor vents selecting, if the engine is cold, because God knows how Aunt Matilda's feathers would get ruffled if the damn car blew cold air on her feet during the two minutes it takes to warm up!

When cold, this sensor bleeds vacuum from the ventilation system if Floor is selected, and interrupts the electrical circuit for the blower. When the coolant warms up, this thing is supposed to open its vacuum circuit, removing the bleed, and close the electrical circuit, restoring power to the blower. Again, it only interrupts when Floor is selected, but it bleeds just enough vacuum in other settings to cause other weirdness, like losing vacuum to the outside/inside intake door, and eventually the other doors and even the temperature control. The device on mine never gets to the warm setting. And there is coolant flow in the heater hose because I can make it damn hot in the car.

I took the car out on the highway, and over 70 MPH, it actually started blowing hot air through the defroster, even though AC through the vents was selected, and set max cool. Let up off the gas and coast, and as vacuum returned, it blew cold through the vents, and switched to recirculate.

I simply took the vacuum connector off of the sensor (R.H. side of engine, in the heater hose) and capped it with black vinyl tape. I also pulled the elctrical connector from the sensor and jumpered the wires together. System now works perfectly.

If you break one of these as I did, just cap the vacuum hoses and jumper the wires, then couple the water hoses together where the thing was. Good as new. Better, actually.

It has always amazed me how poorly this "automatic" climate control works here in Florida. Apparently they don't get much humidity in Michigan. We want to keep our systems on recirculate, even if we're adding warm air to the temperature blend. Outside air is 90%, and it makes a difference in the car when that damn recirc door closes by itself. Now that I've found the thing, I've half a mind to put a vacuum solenoid on it and fix it to manual control.
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