Heat use to blows hot then cold now just hot

SNOWLOVER4U2005

MEMBER
1999 GMC JIMMY
6 CYL
4WD
AUTOMATIC
100,000 MILES

You could hear a motor or something turning under the dash when the heat was on. It would blow cold hot cold hot and continue until you shut it off. The controls work as far as changing the blower speed or where you send the air. Now the truck blows hot air all the time. It wasn't an issue during the winter but its starting to get warm and I have to leave the windows open to keep my cool. Please email me if you know where this motor is. I already have all the panels off the dash but still cant see it. Unless its the motor on top of the air plenum. If that's the case how can I get to it.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

If your vents are only blowing hot air now that is because you have an AC issue.

So, we need to check the pressures and find out if there is even freon in the system.

Here is a guide that will help with this:

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

https://youtu.be/4UjfQKvrB6Y

Basically, we need to hook up a gauge set and find out what the pressure is. I suspect the system is empty which means we need to fill the system and then recheck the operation. This is assuming that you pulled it into a vacuum and found no leaks. If there are leaks, then we need to fix that first.

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

Please run through these guides and then use the chart below that will help with figuring out possible causes of the pressure.

Thanks

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