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Heater works at low fan speed, but at high speed blows cold air

djhb20

Full Member
Joined
Oct 23, 2015
Messages
14
So, the title sort of tells it all

I bought my '03 1500 Z71 at the beginning of fall and so I haven't used the AC or heat much at all. AC seems ok, but I don't know if it has a similar problem or not.

Here's what happens with the heat. If the fan speed is at 1 or 2 (I have analog dual zone HVAc), I get heat coming out the vents, but obviously it comes out slow. If I hack it up to 3 or above, basically just cold air blows through. This has been over the past few days in DC, when it's been down in the mid-30s and 40s, so it's cold outside.

I've tried searching for this sort of problem here and elsewhere (even not specific for an Av), but it seems to be a hard topic to find, or it hasn't happened to anyone else.

Any thoughts on what might be doing it? Obviously, there is heat so that seems to rule out a bad actuator. But, I just don't know. My only thought is that somehow the vent is sucking in outside air or something? Has anyone seen this before or have any ideas?

Thanks
 
Possible issues:
Blend doors
Clogged heater core
Air box has leak to outside near fan intake
 
It was a clogged heater core. Took the hoses off, ran some water through via a garden hose, and I've got heat.
 
djhb20 said:
It was a clogged heater core. Took the hoses off, ran some water through via a garden hose, and I've got heat.
That means your engine could be clogged too....

bad bad... ya need to have the engine flushed with proper chemicals and such...

Have radiator checked etc...

then replace with brand new fresh coolant and distilled water.
 
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