New heater controls-hardly any heat.

[ccreddell]

Ok, so my fan quit and I decided to replace the old broken tabs and grungy heater controls. Now with the old one, I had no fan, but it heated up great once I got moving. Usually had to turn down the temp control no matter how cold it was outside. With the new unit, everything works, it actually lights up, but now it hardly gets warm enough to notice-and that’s with the temp control maxed. Haven’t ever run into that before. Anybody have any ideas? Oh, it’s a 99 2dr Tahoe if it matters.

 

[AK49BWL]

While not common, it is possible to get a bad unit right out of the box... There may have also been a coincidental temp door actuator failure or your heater core clogged up.

Someone chime in here, do those Tahoes have the heat-cut solenoid in the heater core supply line?

 

[ccreddell]

I thought that too. But it’s the same out of the defroster and the dash vents.

 

[AK49BWL]

If the temperature door isn't moving or the heat solenoid isn't open/heater core is plugged, that will be the case... Do you still have the old controller? If so, plug the fan connector into the new one and the other connector into the old one and see if it works like it should again.

 

[RawbDidIt]

Heater core is fed by coolant, what's the coolant temp look like?

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[SUBURBAN5]

If the temperature door isn't moving or the heat solenoid isn't open/heater core is plugged, that will be the case... Do you still have the old controller? If so, plug the fan connector into the new one and the other connector into the old one and see if it works like it should again.

2x this test

 

[east302]

Someone chime in here, do those Tahoes have the heat-cut solenoid in the heater core supply line?

They do. The temperature dial “Max” detent energizes a solenoid which then allows the water valve to close with vacuum from the PCV fitting.

I had a new Dorman control panel that was stuck energizing that solenoid regardless of temp dial position. It lasted five minutes before it started smoking. Piece of sh*t.

Owner should check to see if the two heater lines at the firewall (firewall side of the water valve) are hot and the same temperature as the ones on the “other” side of the valve.

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Feel along the bottom of the valve. There’s a spring-loaded plunger that you can push up and down (opening and closing the valve) with little effort. When the valve is open, the plunger will be down.

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If that and the blower switch swap checks out, see if the temperature actuator (behind the ashtray) is turning steadily and silently - keyword there, it shouldn’t be making any noise. If it’s sounding like gravel inside as it turns, the actuator gears are probably damaged.

The silver dial (position indicator) has a notch which will rotate to align with these outside marks on the actuator. This indicates the position of the damper inside and it should travel completely between those lines from the full cold to full hot dial setting.

If it doesn’t turn at all, it’s either the actuator or the control panel. You’d then pull the actuator connector and check for ground, constant battery voltage and a variable signal voltage on the three wires with ignition on. As the temp dial is turned, the signal voltage will vary... 1 to 12V comes to mind but don’t quote me on that.

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[ccreddell]

Thanks guys, this gives me a place to start.

 

[SUBURBAN5]

Suburbans are like that. Couldn't say about a tahoe

 

[JeremyNH]

I had this problem last year on my 1998 K1500 and it was two things: the blend door actuator had a cracked gear which I replaced and which helped a little and, when it didn't fully fix it, checked the coolant and it was low. Turned out my water pump was leaking just enough to drain the coolant down over time but not so much as to leave a puddle (it seemed to be drying on the mud guard). The heater supply is at the high point of the coolant system so you will lose heater flow before the engine starts to run hot.