Warm air coming out the vents when set on cool!

1bignordic · Jul 24, 2017

Hi everyone! My 1994 K1500 has warm air coming out the vents when the setting is on cool, this is particularly uncomfortable in the hot summer weather. My A/C doesn't work so I at least want to figure out how to repair this issue. Does anyone have any ideas?

Thanks!!!

Bob L · Jul 24, 2017

By warm air are we talking the same as with the heat on or outside temp air? If you are not sure if the blend door is stopping air from going through the heater core try a couple paint sticks clamped onto the heater hoses with vise grips to stop water flow to heater if it gets cooler you may have a blend door motor problem. Get a thermometer to stick into the vents so you really know what temps you are talking about.

I am from the old days where vehicles without A/C had fresh air vents and vent windows so you had direct outside air forced into the car when moving. A/C equipped vehicles have all air coming through the climate system so not as effective without working A/C.

1bignordic · Jul 24, 2017

Thanks for the reply. I'll try the thermometer but I can tell it feels like the heat is on, my cousin was riding with me and he even said something is messed up with your hvac.

I miss the older vehicles that had those wing windows and those fresh air vents on your feet!

Is there a thread on how to repair the blend door motor?

Thanks again!

jollyjerry · Jul 25, 2017

If it does turn out to be the blend door, I think it's behind the dash and a real pita to get to. Someone correct me if I have the wrong actuator though. I think it's 65 in this image. 69 is the mode door which controls air going to the defrost/floor/front.

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Here's a thread about pulling the dash http://www.gmt400.com/threads/dash-replacement.17137/, and you can see the actuator here:

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@east302 helped me with mine a lot, he has a great thread on it also if you search

Bob L · Jul 25, 2017

Someone had it on you tube without pulley the dash. You may need a small hand.

east302 · Jul 25, 2017

I've seen a thread where someone (may have been user @someotherguy ) managed to replace that actuator without pulling the dash.

I think it's kind of behind the ashtray.

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GM01 · Nov 27, 2021

east302 said:
I've seen a thread where someone (may have been user @someotherguy ) managed to replace that actuator without pulling the dash.

I think it's kind of behind the ashtray.

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I know this is an old thread, but figured I could help anyone else who came across it. That blend door actuator will usually make a grinding sound when it's not working properly, and the sound is the ground off teeth skipping internally. They're literally just plastic/vinyl gears in there. I managed to change it out with a bit of squeezing just by taking the glove box out, which was just 4 screws. After that I changed my stereo for a regular single din one, and noticed it would have helped to pop that panel off for this job too. No need to pull dash all apart. I'm still having issues with my vent only blowing warm, moist air when when it's cool outside, so hopefully I can find some help with that now

yevgenievich · Nov 27, 2021

Heater core near by. Adding coolant bypass would help some if not installed

GoToGuy · Nov 27, 2021

On vent setting only, the outside static atmospheric air is drawn into air passages. Then that air is affected by any existing vehicle and ducting temperature. Usually getting warmer before entering cabin. Being moist air felt. If your humidity is high that day and settings on vent it would be normal for warmed air to feel humid. Providing you have no leaks in your water fed heater lines or heat exchanger( heater core). Indicated by visual leaking, wet floor passenger side. Loss of coolant with no external indication. No working AC, hot day might be better, more comfortable with control off instead of vent selected. Good luck.

GM01 · Dec 15, 2021

Just to follow up, I don't know if your issue has been resolved or not, but I learned there are 3 blend doors actuators, the one under the dash on the right side is the one you want(controls taking in outside air vs inside air). Buried behind the cover door and a few other things, real pain to get to. Replaced that one and like magic my warm, moist air was gone, with cool air flowing from outside.

Warm air coming out the vents when set on cool!

1bignordic

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