I have searched for specific topic on here and really not found a solution to the problem I am having. This is a 98 SLT 4-wd w/5.9 with rear heat/ac. Basically no hot heat in front or back with temp control turned to high. At best it will keep you kinda warm at 50 deg. ambient any thing below it is not comfortable. Engine temp is fine,no heater core leaks,no overheating issues,coolant up to level. So I did read about a blender door issue with these 1st gens and would like some advice on that. I believe this may be my problem. All hoses in engine bay are HOT to the touch so I know t-stat is working properly. Several months ago coolant level was a little low so I added approx. 1/2 gal which should not be enough to cause this problem. In the morning if I have frost on windshield I can not even get enough heat to clear frost. Any suggestions? Mornings here in North Carolina are getting cooler so I really need to address this soon.
Thanks All
Augie Dog

 

Augie try what I tried that really made a big difference. I don't know if the rear heat is runs through the front heat. I took the hose from the mainfold to the heater core and the hose from the water pump to the core. I ran water through each direction flushing out the heater core. I was surprised how much stuff was in there. It took maybe 10 minutes.

 

i agree its probably a blend door issue, however idk what to tell you to do exactly to fix it.

 

Are both heater core hoses relatively the same temp at the firewall? If the outlet is cooler, the heater core is plugged. If their both hot, then blend door would be suspect. I would also use an antifreeze tester to make sure that 1/2g you added wasn't to much antifreeze.

 

I did confirm heater core is not blocked. Both hoses are very HOT to the touch. I included the fact it has rear heat/ac simply as a FIY to indicate I was not putting out heat also.I am thinking a blend door.

 

You'll have to pull dash and the HVAC box. This means pulling the A/C evap and heater core. You may want to replace them now while you have it apart or not. The oem heater core is very thin and prone to leaks. The after market heater core replacement is a much better design and thicker.

 

There was never a heat option for the rear in 1998. All you have is a A/C and a fan on the overhead. So when the A/C is on you have a cooler, but other then that it only pushes internal air.

Blow out you heater core on the front firewall.

 

Thanks for that info Hydra. This is not my vehicle,it belongs to a friend so I was not aware of the rear A/C only. That is good to know. She is letting me drive the vehicle while I do repairs on my 2001 D so I thought I would repay her by fixing the no heat problem but it sounds like a major ordeal.

 

hmmm... have you ruled out the water pump as the issue?when my heat stopped working it was a water pump going out. but my heater core also has a leak... if your core is leaking you would smell antifreeze and there would be a white mist comming out of the vents. have you torn apart the dash yet and seen if something is siezed up?