HEAT FROM VENTS

1997 Mercury Marquis

Tiny

highstraight

September, 13, 2010 AT 2:52 PM

Heater problem
1997 Mercury Marquis V8 Two Wheel Drive Automatic 246000 miles

I have a/c that works. I have vent that works.
No defog and heat that comes from the vents.
This is the same thing that happens in a 2005
I know. Must be common.

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3 Answers

Tiny

Wrenchtech

September, 13, 2010 AT 3:13 PM

Are you saying that the mode control doesn't switch the air flow to defrost or bottom vents?

Tiny

highstraight

September, 13, 2010 AT 6:06 PM

In defog mode, there is no output. In heater mode, heated air comes out the vent. A/C and vent modes are fine.

Tiny

Wrenchtech

September, 13, 2010 AT 6:11 PM

The mode control doors on that car are vacuum operated. First check that all the hoses are hooked up and nothing is jammed. If it's an Auto temp control system. There is a module that controls the vacuum. If it's manual, there is a vacuum rotary switch. Make sure you have a full vacuum supply coming in from the engine on the black hose. Measure the vacuum and compare it with manifold direct vacuum.

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