Heater

1990 CHEVROLET CHEYENNE
148,000 MILES • 6 CYL • 2WD • MANUAL
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KMELTON315
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I have a 1990 chevy cheyenne with a 4.3l engine. When heater and defroster on it blows only cold air when even when water temp is hot. What are the causes?
Jan 22, 2011 at 1:43 AM
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WRENCHTECH
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With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If not too hot to hold, then you have to look at the actual engine temp and if that is up, if it is, then your looking at a restricted heater core.
If you find that they are both too hot to hold, then the heat in that vehicle is controlled by a blend door that regulates heated air flow. it is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.
If they are both not too hot to hold on to, then you either have a restricted heater core or the system is not completely full and getting air pockets for some reason.
Jan 22, 2011 at 3:23 AM
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KMELTON315
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Thank you for your response. Next question then is where is the actuator located on this model and how can it be checked?
Jan 22, 2011 at 5:06 AM
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WRENCHTECH
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https://www.2carpros.com/images/external/57432979.gif
Jan 22, 2011 at 12:41 PM