cool air comes out of the heater

2002 HONDA CIVIC
186,800 MILES • 4 CYL • FWD • AUTOMATIC
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BC
  • MEMBER
  • 2 POSTS
When idling, cool air comes out of the heater. When I accelerate, it heats up.
I've added antifreeze, but it doesn't seem to be siphoning from the tank. The temp gauge when warm is in the normal range. I've changed the thermostat to no avail. Any suggestions?
Feb 23, 2011 at 8:01 AM
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KHLOW2008
  • ✓Experienced Mechanic
  • 41,812 POSTS
Pull out the cabin filter and check for clogging. this might seem absurb but the air flow affects the heater temperature. When engine is cold, did you check the coolant level in radiator?

Apr 7, 2021 at 5:09 AM
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BC
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The air flow is fine.The coolant level in the radiator is down 1 inch, and it doesn't draw from the tank.There are no codes.I believe I found the cause. I replaced the radiator cap and it seems to have been corrected.
Apr 7, 2021 at 5:09 AM
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KHLOW2008
  • ✓Experienced Mechanic
  • 41,812 POSTS
When the radiator coolant level is low, it would affect the heating system.

A bad radiator cap would not maintain the required pressure in cooling system and would allow coolant to be pushed out to either recovery tank or through the radiator neck. This would deplete the coolant, at least in radiator. When cooling occurs, air would be be sucked into radiator instead of coolant.

Glad to know you have fixed the problem.

Have a nice day.
Apr 7, 2021 at 5:09 AM
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