Heater not working

1994 GMC C1500
150,000 MILES • 4.3L • V6 • 2WD • AUTOMATIC
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WOPI WELLS
  • MEMBER
  • 2 POSTS
Have changed thermostat numerous times (now has a 205° instead of the 180°), also radiator cap several times (now has locking), new water pump and heater core. Still not getting heat. It also has a new cooling sensor. Please help, we are all completely stumped! God bless!!!
Mar 1, 2022 at 9:09 AM
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WOPI WELLS
  • MEMBER
  • 2 POSTS
It has a new cooling sensor coming out of block. Don't think I've replaced the one by thermostat housing.
Mar 2, 2022 at 5:18 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

When the engine is at operating temperature and heat is turned on, do both heater core hoses get hot? If they do, then it has heat in the heater box which is likely being prevented to enter the cabin by the blend air door.

First, confirm the hoses do both get hot. If they do, locate the temperature door motor (blend door actuator) under the dash and remove it. With it connected, see if it responds when you switch the temperature control from hot to cold and back.

I attached a pic below showing the actuator's location.

Also, here is a link that explains how in general to replace one. You may find it helpful.

https://www.2carpros.com/articles/replace-blend-door-motor

Let me know what you find.

Take care,

Joe

See pic below.
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Mar 2, 2022 at 10:35 AM
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