I just bought a 1998 Newmar Mountain Aire with a Chevy 454. I turned on the dash heat, and it blows cool air. The air conditioning works great. The blower also works fine. Just no dash heat. Engine temp. is a constant 165. I tried to locate the heater core, to see if the controls were disconnected, but couldn't find it. Does anyone have any suggestions?

Flush cooling system, make sure heater core isnt bypassed. Make sure also that coolant level is correct. start engine cold with radiator cap off and watch coolant level. see if it drops when thermostat opens and then add proper coolant. Also be a blockage in heater core or a collapsed hose.

First of all, I am no mechanic by any means. But your problem could have to do with the vacuum system that switches the airflow from heat to vents, to defroster etc. If that is your problem, then when you reset your control from say vent to heat it is not switching the vent internally. I had this problem on a GM passenger car once. Just guessing. Good luck!

Also check the coolant control valve that most likely on the outside of the firewall from the heater core. I think others have had problems with this valve not opening or closing.

Then there is possible low coolant which starves the heater core first due to it being at highest point in system. Always check when engine is cold and no pressure is present in lines. You may also have a mechanical inline heater valve in the hose going to the heater core that is not connected or stuck closed. That would be controlled by the dash heater lever and connected via a cable to the inline valve.

I also recommend you check the heater core valve. It's under the hood and is run by 12v or in some cases vacuum. It will be right inline in the heater core inlet hose. Most likely its not opening correctly. Very common issue.

Dash heat only blows cool air | Good Sam Community

13 Replies

Gasman_2
Explorer
Jan 10, 2014
Also check the coolant control valve that most likely on the outside of the firewall from the heater core. I think others have had problems with this valve not opening or closing.
msredneck84
Explorer
Jan 10, 2014
First of all, I am no mechanic by any means. But your problem could have to do with the vacuum system that switches the airflow from heat to vents, to defroster etc. If that is your problem, then when you reset your control from say vent to heat it is not switching the vent internally. I had this problem on a GM passenger car once. Just guessing. Good luck!
Davidlatham2012
Explorer
Jan 10, 2014
Flush cooling system, make sure heater core isnt bypassed. Make sure also that coolant level is correct. start engine cold with radiator cap off and watch coolant level. see if it drops when thermostat opens and then add proper coolant. Also be a blockage in heater core or a collapsed hose.

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Dash heat only blows cool air

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