1997 Silverado 5.7L. Lost hot air from heater. A/C works fine, just nothing when I turn control to warm. I've flushed heater core, replaced control unit, actuator behind glove box, and actuator in the middle behind ash tray. Still no heater. I can feel both actuators moving but nothing. Please give me some more ideas. Thanks, Danny

 

Touch both heater hoses at the firewall when the motor is completely hot.

These questions need to be answered.

1. Did you install a 195F degree thermostat? If not, change it to a 195F only.
2. Are the both hoses hot?
3. Is one hose is hot, is the other heater hose at a lesser temperature with the heater running?
4. Are both hoses somewhat cool to the touch?
5. Is your truck equipped with a "water temp valve" connected to the heater hoses?
6. Is the upper radiator hose the same temp feel as the heater hoses at the firewall?
7. Is the radiator full to the cap with antifreeze?
8. What does the temp gauge on the dash show when fully warm? A picture of this would be good for evaluation.
9. Turn heat ventilation to high speed blower, "full defrost mode", then touch the vents at the windshield, ...is it hot there?

 

I agree with oilcanhenry. My 93 silverado with a 5.7 was purchased last month it would not go beyond 140 degrees. It would not even defrost the windshield. I changed the thermostat to a 195 and it runs normal temp and i have heat and defrost.

 

The actuator could be moving just fine but if the shaft that rotates the temp door is broken then it has to be replaced.

Verify by removing the actuator and manually rotate the door with the AC on. The temp should change quickly at the vents if the door is functioning.

If the shaft is broken it’ll feel completely free spinning or have a kind of spring-like resistance to turning if partially broken.

 

Work on Oil Can's list 1st - nice trouble shooting guide.

 

Thanks for the help
1. don’t know what thermostat is in it, but it was working fine then just stopped
2. The hoses are hot… both real hot. I flushed the heater core
3. Both feel the same..the heater box inside is real warm on the bottom
4.hoses are hot
5. no water temp valve
6. seems that upper hose feels the same
7. radiator is full
8. truck runs at about 200
9. I can’t get warm air anywhere

im not sure that the fresh air actuator is working correctly, but don’t know if that will affect temperature or not,
also, the temperature actuator only moves about a quarter turn. Don’t know if that is normal or not.

​​​​​​​Thanks

 

You don't get any heat anywhere on your Chevy at all, but the climate control box does get warm/hot?

 

Yessir it does

 

This condition is mysterious to me. Does the fan work? Is it possible that something is plugging up the air going into your HVAC system? You have no heat coming out at the floor?

 

I’ll try again…