1996 Tahoe - No Heat / Heater blows cold air - HELP!

[Peyton Gregory]

1996 Chevy Tahoe LT 4-Door 4x4.

This past summer/fall I replaced the radiator, water pump, ac condenser, ac compressor, thermostat, hoses, power steering pump, gear box, HVAC control valve, HVAC vacuum line, Heater core, topped off fluid and radiator cap.

When I turn on the heat inside the cab cold air blows from the vents. I removed the blend door actuator next to the accelerator pedal to manually switch the vents. Cold air blows no matter what the setting it.

The heater core and hoses are getting warm/hot.

There's no vacuum pressure coming from the HVAC solenoid on the firewall to the HVAC control valve. There is vacuum pressure going to the solenoid from the intake. Should there be vacuum pressure or no vacuum pressure on the HVAC control valve when the heat is on?

Is there a way to manually change the temperature setting from cold to hot if the HVAC temp controls don't work? Manually open a vent or something to allow heat to flow without purchasing new HVAC controls?

Should the vent/flap above the heater core and under the glovebox be open or closed when the heat is on? Right now it seems to be jammed in the closed position.

Any help is appreciated. It's getting cold...

 

[dbbd1]

Might have better luck with a response in the correct section...

This is the 2015+ section...

 

[Peyton Gregory]

Might have better luck with a response in the correct section...

This is the 2015+ section...

Ahh! You're right, ty

 

[dbbd1]

I used heatertreater.net on my '99 Dodge Ram. You may want to check them out, maybe that would solve your issue.

 

[warndogg]

Have you checked the heater hose going into your heater core on the firewall side? If it's hot there you could have a blocked heater core. Also check the solenoid on your HVAC control right above that hose. You should be able to manually move it over to turn the heat on if that's happening you either have a bad vacuum, you switched one of the vacuum lines (there are 2 there that look simular) or your HVAC solenoid is bad. Good luck.

 

[east302]

When I turn on the heat inside the cab cold air blows from the vents. I removed the blend door actuator next to the accelerator pedal to manually switch the vents. Cold air blows no matter what the setting it.

The actuator by the gas pedal controls the floor-panel-defrost setting...the Mode actuator.

The actuator that controls air flow over the heater core is roughly behind the ashtray. Pull the glovebox to get a glimpse of it.





There is a notched dial that serves as a position indicator. Turn the control panel temperature dial from cold to hot and see if that dial turns smoothly.

The heater core and hoses are getting warm/hot.

They should be pretty hot, so you should have coolant to the heater core. If there is absolutely no change in air temperature, it sounds like it's going to be an actuator, damper or control panel/wiring issue.

There's no vacuum pressure coming from the HVAC solenoid on the firewall to the HVAC control valve. There is vacuum pressure going to the solenoid from the intake. Should there be vacuum pressure or no vacuum pressure on the HVAC control valve when the heat is on?

The solenoid is energized (12V) from the control panel when the temperature dial is set to the full cold detent. Vacuum is applied to the valve, it closes and, in theory, a/c performance is maximized because coolant is not flowing through the heater core.

No, there will be no vacuum applied when the heat is on--the control panel only energizes the solenoid (which applies vacuum) when the temperature dial is turned to the cold detent (MAX setting).

With no vacuum (and an open valve), the plunger on the bottom of the valve will be down. Reach under, you should be able to push it up and down. If it is in the up position, it means that it's closed and no coolant is going to the heater core. The valve is spring return, so it is normally open and would fail in that position (plunger down) if vacuum is removed.

Is there a way to manually change the temperature setting from cold to hot if the HVAC temp controls don't work? Manually open a vent or something to allow heat to flow without purchasing new HVAC controls?

You'd have to see what the temperature door actuator is doing (see diagram above). There may be a way to pull it and manually turn the damper, but it's a pain to get to. If that dial isn't turning at all, I'd probably try a new control panel. If it's turning but jerking/hunting then I'd look for another actuator.

Should the vent/flap above the heater core and under the glovebox be open or closed when the heat is on? Right now it seems to be jammed in the closed position.

That's the recirculation door. It's closed when the recirculation button is pushed on the panel