Question about 1988 Lincoln Town Car

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Vacum leak ? air comes from vents when driving when not turned on

88 towncar 73000 miles when i hit about 40mph i start getting hot air coming from the vents when i let off pedal it goes away also when i have ac on when i step on gas cold air stops coming from vents i know it vacum but the whole car has so many vacum lines last thing is my parking break release valve is hissing its under the dash looks like a half shaped moon could the be causing the whole vacum in the car the screw up?

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If you hear a hissing sound and its comming from a valve or a hose you have a vaccum leak. And yes this could cause your heat to mess up. it all works off vaccum weather you control the knobs or not. When the vuccum increases or decreases. it will move the blend door to difernt positions.

Posted on Dec 29, 2009

  • dean johnson Jan 14, 2014

    yes a vacum leak is your problem, I would be willing to bet that your cruise control is inop as well, upon acceleration vacuum is weak and when you decelerate vacuum is increased. repair the leak you have or plug the side with vacum in order to test. if blend doors and heater as well as a/c works you have found the problem. also there's a vacum switch at the base of the steering column that is notorious for leaking, if so replace. good luck


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Sounds like your blend door is loosing vacum check for melted or disconnected vacum hoses (most are plastic) the blend door is controled by one black and one black w/green stripe. As for the e break check for connection or cracked or worn hose end

Posted on Sep 13, 2009

  • dean johnson Sep 13, 2009

    almost forgot the blend door vacum lines are at the firewall coming through a rubber gromette and then to the source vacum which im sorry to say without a vacum diagram in not quit shure where that is good luck

  • dean johnson Sep 13, 2009

    found it there is a solenoid on the passenger side in line of the heater core supplu hosed it has two wires one orange and one blue with a green tracer this is where the two afore mentioned vacum lines attache i had the same problemb and now all is well the fan even stays at the same speed even under acceleration and the ac/ and heater seems to be in perfect working order



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How come I get hot air from my cars vents when I turn the air conditioner on.

If the hot air only comes from the defrost it is probably the Control Head. Can be rebuilt for 100 or replaced quick for $235. The Blend door is expensive because of the labor to get to it. Alot of places will diagnose your problems for $25 to $85. They can check the vacum pressure from under the dash and let you know what is wrong.

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Well maintained a fleet of trucks and ran 20-40W all year long.Years ranging from 88-06 and never has a problem.Sounds like you may have a bad vacume line. Could be a problem with your EGR valve or the IAC (idle Air Control) Valve if equipted.Would start checking the vacume hoses first.Well hope this helps and good luck.

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Ac seems to come on but air not blowing through the vents. the fan is working. i can hear it but nothing comes through the vents. you can feel some cold air coming from behind the dash.

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Air vents

I was having a similar problem with the vents not redirecting air when selected. I went onto the auto zone wed site and found very helpful schmeatic diagrams for electrical and vacume systems. That lead me to investigate a possible vacume leak. There was a vacume hose broken tucked away by the battery. I repaired the hose with thick wall heat tape and now the vents move normally. The vacume starts on the P/S top of engine runs by the battery into the fore wall. Once in the P/S foot well you will see a purple hose that you can quickly check the vacume pressure. It should be a noticable vacume. If not work your way back to the engine. If you do have a good vacume there then I would suggest going to a auto wreckers and picking up a new heater control module for around $90.00 in stead of the $240.00 fro the dealer. All you need is a phillips screw driver to replace it.

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