2002 Pontiac Grand Prix Heater

HULSMAWJ

MEMBER
2002 PONTIAC GRAND PRIX
3.1L
6 CYL
2WD
AUTOMATIC
150,000 MILES

Air flow restricted through heater. No restriction when manual temperature control lever is set to cold, as manual slider moves to warm restriction increases. At max heat setting flow is restricted 80%. Occurs in all settings - dash output, floor output, defrost output. Consistent on both left and right side controls.

Blower motor works well - no sound difference with adjustment.

5 Replies

HMAC300

MECHANIC
48,601 POSTS

Check for a vacuum leak see pic at air inlet door

Image (Click to make bigger)

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Saturday, December 12th, 2015 AT 11:43 AM

HULSMAWJ

MEMBER
3 POSTS

The diagram helps to understand the system. Thank you.

However it is not clear how the air inlet door position would restrict air flow when the air temperature selector is moved from cold to warm. Please explain.

Also not clear how the left and right air flow remain separate in the diagram. Please explain.

Thank you

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Saturday, December 12th, 2015 AT 3:01 PM

HMAC300

MECHANIC
48,601 POSTS

The L & r air movement is controlled by electric actuators you can try pulling hvac fuse inside car to reset them otherwise it will need to be scanned to see if control head is sending power to them. It would be the electric actuators that will be screwing up not a vacuum leak like I said previously. If the actuators work then it may be broken doors for heat not allowing the door to move. So try the fuse thing. Pull it with key on for 60 seconds.

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Saturday, December 12th, 2015 AT 3:51 PM

HULSMAWJ

MEMBER
3 POSTS

Going back to your original theory that the air inlet selector is malfunctioning. I rechecked the conditions. The air flow is normal when the air temp is cold on all modes EXCEPT defrost. In that mode the air flow is normal when the air temp slider is hot. (Opposite)

What determines when the cabin air is the input air and when the outside air is the input air? Could it be that the outside air inlet is restricted?

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Saturday, December 12th, 2015 AT 4:13 PM

HMAC300

MECHANIC
48,601 POSTS

It cold be but scanning will show that. You might have a bad mode vacuum motor or a vacuum leak going to that as it kind of looks like the air direction isn't changing like it should. Other than that I have no further suggestions.