1994 Mercury Marquis air conditioning sometimes blows hot a

1994 MERCURY

MEMBER
1994 MERCURY MARQUIS
V8
2WD
AUTOMATIC
180,000 MILES

My 1994 Grand Marquis air conditioning will work one day and the next day it will blow only hot air. Then a few days later it will work again. The Freon is charged and the canister under the hood is cold and the air conditioning pump seems to cycle like it should. It comes on and runs for awhile. It doesn't short cycle like they do when they are low on freon. What could be the cause of my air working great one day and the next day it blow really hot air?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

I believe there is a problem with what is called the blend air door. It is a door that opens one direction to allow AC enter the car and the other for AC.

THe blend air door is located near the heater core (not easy to get to) Some are actuated by electric and others by vacuum. Based on your description, it sounds like it is bad and only working on and off.

Let me know what you find.

Joe

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Wednesday, June 9th, 2010 AT 9:05 PM

1994 MERCURY

MEMBER
2 POSTS

I looked under the dash and found 3 vacum controls that open doors when you change the air flow (Defrost, floor, vent) and they all seem to work. I did not find a vacum control that controls anything when you switch from air to heat. Can you point me to a specific spot for my 1994 mercury? Could it possibly be a plugged orfic or something? How would I tell if it was a plugged orfice?

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Tuesday, June 29th, 2010 AT 10:28 AM

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

It is located on the near the heater core. Here is the best picture I could find of the vacuum diagram for the system. It does identify the blend door. I just hope it is big enough for you to read when I send it or you can enlarge it. Let me know if it helps.