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How do I change a heater core in a 1991 GMC Sierra is there a site that I can go to that shows how ?

The truck does not have ac where can I buy a defrost bland door

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It sounds like the bypass valve is stuck open. Check bypass valve and vacuum hoses attached to it.
Hope this helps.

Jan 06, 2015 | 2005 GMC Sierra

1 Answer

Is there a site i can go to show how to change heater core on 1991 gmc 5.7 motor make a free account, login, put in the year, make and model. Look at the free repair guides.

Dec 12, 2014 | GMC Sierra Cars & Trucks

1 Answer

How do i remove a heater core on a 5.7 liter motor

you left info for a 91 gmc sierra no such thing try again

Nov 08, 2014 | 1991 GMC Sierra

1 Answer

Which hose on the heater core is the heater inlet hose on 2001 gmc Sierra 5.3l

the hose from the intake to the heater core is always the inlet , it is usually the one closest to the engine the return is the one closest to the fender or ac box

Sep 01, 2014 | Cars & Trucks

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1991 gmc sierra 1500 p/u-can not locate blower motor speed control resistor. I've looked under dash, pulled out glove compartment, looked on firewall, I give up.

If its not near the blower motor, it may be on the hvac box on the firewall in the engine compartment. It depends on if it has ac or not.
They are usually behind the glove box mounted in the side of the heater box.

Sep 26, 2013 | 1991 GMC Sierra

1 Answer

2003 gmc sierra heat will not blow hot air. Changed thermostat, resistor, both heater core hoses are hot to touch and the coolant is full

if the blower motor motor is working then its a blocked heater core or a faulty shut off valve ,i would need to get my head under the bonnet and then the dash to find the fault to be honest

Nov 06, 2011 | 2003 GMC Sierra

1 Answer

How to replace heater core

Dec 02, 2010 | 1991 GMC Sierra

1 Answer

At idle, Heater Core Return Line is flowing only

two things--first replace your cabin air filter.second reverse flush your heater core with a garden hose and that should remove the build up of material in your heater core and restore the flow,hope this helps

Oct 21, 2009 | 2000 GMC Sierra

1 Answer


be more specific,head unit could mean cylinder head/s could mean thermostat unit,were the hoses hooked up right? thermostat should be checked before installing,very easy to do could be stuck shut.was the heater core checked or flushed out?lots of maybys,wish it was in my garage..

Oct 16, 2008 | 1991 GMC Sierra

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