Heater blowing cold air

AMANDA79

MEMBER
1994 GMC C2500
5.7L
V8
2WD
AUTOMATIC
180,000 MILES

I just picked up this truck and have been told that the heater core is new and recently installed. It is blowing cold air or air that is slightly warmer than outside. The engine heats up to a normal temperature but does not overheat but still no warm air. I have found that when the blower is turned any higher than medium the blend door is clicking. Could that cause the air to run cold or should I be looking for other problems as well?

Thursday, December 7th, 2017 AT 5:08 PM

1 Reply

PATENTED_REPAIR_PRO

MECHANIC
1,853 POSTS

See if you have a heater control valve on one of those heater hoses and if so, feel the heater hose just before and just after that valve. If it is hot in front but just warm after that vale (if equipped) is stuck closed or maybe a vacuum hose fell off of it, etc.
Other than that both heater hoses going into the firewall to the heater core should both be hot. If one if hot and the other just warm, the heater core is clogged, but I doubt that since you said it is new but you should still check. Also, make sure the coolant level is full.

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Thursday, December 7th, 2017 AT 5:16 PM