99 GMC Yukon no heat

[the 18th letter]

About a month ago blower stopped working. Loaded the parts cannon changed blower, still no blower. Changed resistor, still no blower. Changed the Heat/AC control and the blowers back on but now I got no heat. WTF All suggestions welcomed.

 

[Joseph Garcia]

When the heat and blowers are turned on, do both heater hoses in the engine bay feel hot? You'll want to be sure that you don't have a heater core obstruction.

@swathdiver may be able to provide some troubleshooting input for your issue.

 

[Eman85]

Are the heater hoses both hot? Does the temperature door actuator move when you rotate the temperature control knob?

 

[the 18th letter]

When the heat and blowers are turned on, do both heater hoses in the engine bay feel hot? You'll want to be sure that you don't have a heater core obstruction.

@swathdiver may be able to provide some troubleshooting input for your issue.

Are the heater hoses both hot? Does the temperature door actuator move when you rotate the temperature control knob?

I’ll check both of these things out. As far as the temperature door actuator moving, I’m listening for the noise? Is there a visible inspection I should be doing as well?

 

[the 18th letter]

I went for a ride today and I can hear the mechanism moving in the dash when I set temp from hot to cold and back. In addition, the air was see your breath cold with the temp set to cold. I felt the upper and lower radiator hoses and the uppers warmer than the lower. There’s a coolant leak as the reservoir was empty but radiator was still pretty much full.

 

[east302]

Do you have rear heat and does it work?

The front heat actuator is behind the ashtray and has a notched dial on it. You’d want to see if it has equal travel from cold to midpoint and midpoint to hot when adjusting the dial.

 

[the 18th letter]

Do you have rear heat and does it work?

The front heat actuator is behind the ashtray and has a notched dial on it. You’d want to see if it has equal travel from cold to midpoint and midpoint to hot when adjusting the dial.


View attachment 445761

No rear heat. I saw your post about this in another thread today and will give it a look. I’m suspecting a defective part as prior to the issue and change of the heat/ac control, my heat was “can you turn the heat off” hot. Even with the slow coolant leak.

 

[east302]

Sorry, so it didn’t come with rear heat or the rear heat isn’t working either?

If it didn’t come with rear heat, the panel may not be sending a signal to the actuator. There would be three wires to its connector - ground, battery and signal voltage. The signal voltage should vary as the temperature dial is turned but I don’t recall the range. Maybe 1 to 5V or 1 to 12V. So if the actuator’s dial doesn’t rotate, that’s the next thing to check.

Another thing to check is the water valve on the heater hoses. It closes when the temp dial is on “Max” and, via a solenoid, shuts off coolant to the heater core to maximize a/c performance. I had a dorman a/c panel several years ago that sent a constant signal to that solenoid and kept the valve closed regardless of dial setting. Then it started smoking so I yanked it out pretty fast.

Piece of junk, lol.

Unplug the wire connector to the solenoid for a quick check. It’s above the heater hoses with one vacuum line to the PCV fitting and a second to the water valve. If you’re getting 12V on the connector regardless of panel temperature setting, then the panel is probably bad.

The valve has a metal rod and plunger on the end. If it pushes up and down easily then the valve is open. In the up position the valve is closed.