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David Craig
David Craig, A.S.E. Certified Master Tecnician
Category: Chevy
Satisfied Customers: 17
Experience:  22 years Experience as a flat rate mechanic. I excel in engine diag. Trans. and electrical.
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2007 Impala: blows cold air..I rev the engine to 2000-3000 rpm..cools

Resolved Question:

The heater on my 2007 Impala blows cold air at idle but almost instantly blows hot air when I rev the engine to 2000-3000 rpm. I immediately cools off again at idle.
Submitted: 7 years ago.
Category: Chevy
Expert:  David Craig replied 7 years ago.
Hi, welcome to Justanswer,
How many miles are on the car? Has it had any work done to the cooling system lately?
Customer: replied 7 years ago.
49000 miles with no cooling system work. The problem just started about a week ago.
Expert:  David Craig replied 7 years ago.
O.k. Thanks, XXXXX XXXXX gets in if work was just done, or if it had hi miles, I would say heater core starting to clog, but I don't think so in this case.

There is an internal G.M. bullitin for this problem. It involves Purging the cooling system. Here are the steps;

•With the engine cooled off, remove the coolant pressure cap.
•Remove upper heater core hose from the metal pipe on the engine.
•Add coolant to the metal pipe, until full.
•Raise the rubber portion of the heater core hose as high as it will go with it still attached at the heater core. Using a funnel, add coolant until the hose is full.
•Reconnect the heater core hose.
•Start engine, have assistant raise the RPMs to about 1500 to 1700 RPMs, top coolant off at engine, then before lowering engine RPMs, install the coolant pressure cap.
•Fill coolant reservoir as necessary, then check the heat at idle.

If this doesn't help,A Coolant Vaccum fill system might help. But I think this will take care of it.
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