Heater control valve

NMARTINEZ

MEMBER
2002 FORD EXCURSION
6.8L
V10
4WD
AUTOMATIC
140,000 MILES

Heater control valve, the vacuum line connected to it always has vacuum, it wont allow the valve to open. I unplugged the line to it then it opens and let's hot go through, what makes vacuum to this line?

Tuesday, September 20th, 2016 AT 6:56 PM

1 Reply

CARADIODOC

MECHANIC
33,917 POSTS

The vacuum is switched at the heater controls. The valve blocks coolant flow when you are running the AC so it does not have to work so hard to cool the air. The AC runs in defrost mode too to remove moisture from the air before it gets blown onto the cold windshield where it would condense, but the heater control valve stays open in that mode so the air gets warmed up.