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1995 GMC Yukon Very little heat in CAB when driving.

Tiny
TRUCKERDEE
  • MEMBER
  • 1995 GMC YUKON
  • V8
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
We just bought a 1995 yukon the heater works great when we drive in town or just idle around, but when we take it out on the road it cools down. We changed the thermostat, heater core, temperature control valve. What else can it be? The large line at the heater core gets hot and the other one that comes out of the heater core is cold. We put in a new heater contol valve also.
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Friday, January 2nd, 2009 AT 10:14 AM

3 Replies

Tiny
JAMES W.
  • MECHANIC
  • 2,394 POSTS
Check vacuum at the heater control valve. You will have more vacuum to the valve cruising around town than you will on the highway. If the vacuum diaphram has a pin hole in it. It might not opening all the way.
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Friday, January 2nd, 2009 AT 12:00 PM
Tiny
TRUCKERDEE
  • MEMBER
  • 2 POSTS
We replaced the heater control valve.
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Friday, January 2nd, 2009 AT 12:33 PM
Tiny
JAMES W.
  • MECHANIC
  • 2,394 POSTS
Did you have vacuum to the new valve? Also, is the blend door in the heater box under the dash moving from cool to heat and back all the way?
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Friday, January 2nd, 2009 AT 8:39 PM

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