No rear heat

BROMAN6

MEMBER
2002 CHEVROLET ASTRO
4.6L
6 CYL
2WD
AUTOMATIC
111,222 MILES

Blows only cold air, both coolant hoses are not warm. Recently replaced the HVAC control valve because there was a crack on the output side. Is it possible that the control valve is stuck close? I verified there is vacuum going to the valve. Front heater works fine, all settings. Coolant level is good. Front heater works fine, all settings. Coolant is topped off.

2 Replies

KASEKENNY

MECHANIC
18,907 POSTS

The place to start is to go to the rear heater core and check the temperature of the hoses going in and out. They should be about the same temperature.

I would use a laser temperature gauge to do this so here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-use-an-infrared-temperature-meter

Basically, if the heater core is restricted then the hose temperatures will be very different and that is a sign that the coolant is going back but not flowing. However, if they are both cold then I suspect the heater core is completely clogged and there is no flow back to the heater core at all.

If this is not the issue, then the control panel would be the next likely thing but here is a guide that will get us a little further with this issue:

https://youtu.be/SNRb6pSwYuU

Please see the attached info on how to replace the heater core because I am going to suspect this is the issue.

Let us know what you find.

Thanks

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