No Heat

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Schurkey

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I have1999 GMC Yukon with barely any heat at all, especially when driving. I have a brand new radiator from champion aluminum radiators, I think a 195 degree thermostat? A new heater core, and new temp mature control actuator, also new heater hoses all through out. The hvac box seems to be hot like there is flow in the heater core with hot coolant, but out of the vents to barely any heat and driving it’s honestly just cool. What am I missing here?
I have confirmed that blend door isn’t stuck, I did replace the actuator with one from my gm dealer, and it operates with no binding, cooling system is full and completely bled of all air, I do indeed have the heater control valve since mine is an suv, I’m completely at a loss of what to do?
1. You use question marks after making statements. Should be periods.

2. Having LESS heat when driving reminds me of my truck. 30+ miles at highway speed, and I had to wear a snowmobile suit because the cab was still so cold. Replaced heater core, added 205-degree thermostat. Nothing helped, so I ignored it for a few years. Wasn't the heater at all--it was a rotted foam gasket, between the metal cowl structure and the plastic of the air inlet above the HVAC blower motor. Bleeding so much cold air into the cab that the heater--which was working just fine--couldn't keep up. The tell-tale was SWMBO stuck her hand under the passenger-side dash, and felt the cold draft. Had to remove the steering column, disassemble the dash to get at the gasket. Replaced the GM foam with home-improvement store foam tape. Been good for almost a decade now. (Except for needing a new thermostat years later.) And of course, it gave me an opportunity to pick all the pine-needles out of the evaprator core.
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Replaced ALL the foam gaskets with the same foam tape, while I had all this apart.

3. What is the actual temperature of the air coming out the vents?

4. Do you truly have a 195 thermostat? Sounds like you're guessing at the thermostat rating. What temperature is the dash gauge indicating? I had the clue that my thermostat failed when the gauge took forever to get 1/4 above the "cold" peg.

5. You say the heater control valve works without binding. Are you testing it with vehicle vacuum or by pushing the lever on the valve itself? If you're pushing the lever...have you checked for proper vacuum to the valve port?

6. As asked prevously--do you have good airflow at the vents? This is not a matter of the cab being cold because there's not enough air...right?

7. The quick-coupler for the heater core is restricted--intentionally--but I don't know how it could be "damaged". Might be plugged, though--but then the heater box wouldn't be hot.
 

Matt Vaughn

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Have you checked the temperatures of the inlet and outlet hoses on the radiator? If everything else is working as you indicated, then it would seem to have to be the thermostat.
They seem to be very similar in temps, both hoses when I reach operational temperature is pretty hot
 

Orpedcrow

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They seem to be very similar in temps, both hoses when I reach operational temperature is pretty hot
It could still be the blend door itself. Does the air temp at the vents change at all when changing the temperature at the control panel?
 

Vikingdude

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Finally found the screenshots in my phone. Maybe this is helpful to someone.
 

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JeremyNH

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This happened to me 3 years ago (98 K1500 5.7L). Ended up being the blend door actuator. I replaced it with a Dorman 604-107. I took the old one apart when done. It had blue internal gears like what Vikingdude has posted. The main drive gear (the bigger one the actuator connects to) was cracked. The actuator was a pain to replace because there wasn't enough room to get the hold down screw off with the dash in place. I had to drop the steering column and loosen the dash so that it fell forward about 2" to get the room to get the actuator off and the new one on. There's a reset procedure for getting the actuator encoders to realign (negative terminal off battery for a minute, power back on, turn key to run but not start and leave there for about 45 seconds as the actuators all move through their range of travel, key off and then good to go). No problems since.
 

Matt Vaughn

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Hoses are installed correctly? In the photo below, the top one is from the intake, the lower from the water pump.

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At the bottom of the water valve, there is a spring-loaded plunger/shaft that moves up and down. When down, the butterflies are open. See if it returns to the down position with engine off. With engine on, see if it is down. It goes up (closed) with the temperature dial in the MAX detent to assist with a/c performance.

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The heater door actuator has a silver position indicator dial on it. See if it turns smoothly from one hatch mark to the other as the temperature dial is turned - roughly 11 to 1 o’clock positions. Might have to pull the glovebox and get creative to see it. That is the one that you replaced, right? Not the one by the gas pedal.

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And last, there is a plastic restriction built into the heater hose connector at the intake. @Schurkey could elaborate, but if it’s damaged then it could impact coolant flow.
Yes, I replaced the one behind the ashtray. Maybe I’ll warranty it out with another one and try a relearn, I also have replaced the panel with a doorman product also.
 

east302

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Yes, I replaced the one behind the ashtray. Maybe I’ll warranty it out with another one and try a relearn, I also have replaced the panel with a doorman product also.
If the position indicator dial on the actuator turns between the marks, then it is getting a signal from the panel and should indicate that the damper is not jammed.

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Is the water valve closed (plunger drawn up into the valve)? Reason I ask is that I put a dorman panel in my Tahoe two or three years ago. Regardless of temperature dial setting, it sent 12V to the water valve solenoid and kept the valve shut. Then the panel started smoking and that was that.
 

Schurkey

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Had the K1500 out for a drive for the second time since replacing the thermostat. I think the new 'stat is defective, temp according to the gauge goes up 'n' down between 190-ish and 220-ish as if the 'stat can't make up it's mind whether to open or close. But it beats the "tap the gauge, I don't think it's working... previous thermostat that wasn't going more than 1/4 the way up the scale.

Anyway, my air-vent thermometer shows about 170-degree air at the dash vents when the HVAC system is set "full-hot" and "Vent". No recirculation. And it didn't seem to vary much even though the dash gauge was moving up 'n' down.

Note that I have not verified this thermometer, or the gauge/sending unit. But I have no reason to doubt them. The temp is higher on the dash gauge, and the heat is better.
 
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