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air pockets in the cooling system, start by bleeding the lines, plus there is a bypass for the heater core when you have the a/c turned on, or your heater isn't on, this fluctuate between makes and models. but i would go to YouTube and look up how to bleed coolant lines, and that should make it easy for you.
What else can I help you with?
How do you install a heater core in a gmc sierra 1500 4.3L v6?
how do you install a heater core for a 2003 gmc sierra 4.3l truck
Where to find a fuel pump fuse on a 1999 gmc truck?
where i the fuse for a fuel pump on 1991 gmc truck
How hard is it to replace the heater core in a 1999 GMC Suburban?
Answernot hard
Why does my 1999 gmc jimmy only blow cold air even if the truck is at 210?
You need to back flush the heater core have had to do it to my jimmy 2 times and fixed the problem is easy fix .
How do you change the heater core on a 1996 GMC half ton pickup?
The 1996 GMC half ton pickup truck heater core can be removed by removing the heater core retaining bolts. Remove the heater core water lines. Reverse the process to install the new heater core.
Where is the heater inlet hose located on a 1992 GMC Sierra 5.7 liter truck?
I Don't Know Sorry
In what year was the GMC Sierra 3500 first made?
The GMC Sierra 3500 truck was first created in 1998 for the 1999 release. The GMC Sierra 3500 version from 1999 to 2007 is considered the classic version.
Where is the heater core located on a 1999 GMC Yukon?
On the rider side firewall in the engine compartment ?
What is an ecu for an 99 gmc suburban?
An ECU is essentially the brain for a 1999 GMC Suburban. Without an ECU the truck will not be able to operate at all.
How do you remove the spare tire of a gmc sierra 1999 truck?
1987 Sierra classic 2500 GMC Removing spare tire and assembly
Where is the actuator door on GMC Sierra truck heater and why does it not open close for the defroster?
This is under the dash and just to the right of your gas peddle.
Can you patch a heater hose on a 1999 gmc suburban?
No you can not, It is under to much pressure when engine is running. NEED to REPLACE IT.
