The thread that won't die! LOL
I'm back. Since acquiring and driving other vehicles, I haven't worried much about the 02 S-10 for awhile. But now it's cold again and this truck, with good tires, is great in heavy snow. So I've been driving it a bit again lately and that means thinking about the heater problem I never spent time on.
I had been resigned to just getting a portable defroster/heater and forgetting about repairing the truck until I realized that the wimpy little heaters designed for 12v systems only draw a max of about 300 watts, which when converted to heat, is barely enough to defrost a small portion of the windshield. Nearly all of the reviews I've seen of them are poor. I thought about rigging up some batteries to provide 24v, but even at that, the 24v heaters only draw about 600 watts, which still amounts to only half of the wattage of a hair dryer or a small space heater.
Long story short, I've almost given up on the defrosters and might tear into the truck.
I reread this thread and spent some time looking at other threads around the net. The story with my truck is that the transfer case vacuum switch failed (according to the dealer), which almost certainly allowed enough oil to be ingested in one or more vacuum lines. While 4-wheel drive works, the HVAC control unit does not work and there remains a hissing sound in that area. I have assumed that the control module must be faulty. Because it operates by vacuum, it is possible that oil made it through the lines to that unit.
It's not my first concern because I want to see what I can do without tearing out the dash. Also, supposedly, if there is a vacuum failure, the system should fail to a mode selection of heat and defrost. This is a functional mode. It may also be possible to close the vents to assist in maximizing airflow in this failsafe mode.
So before tearing into the dash, I had a look at a couple of things mentioned in this thread and others.
1. Blend door actuator, rod, and door. I opened the glove compartment and operated the hot/cold selector and could hear an electric sound but could not see the metal rod moving, and consequently, the blend door doesn't seem to move.
2. In the engine compartment with the hood open, on the drivers side between the brake master cylinder assembly and the fender is a little plastic connector that joins vacuum hoses together. This is a common point for vacuum hose deterioration and sure enough, I found some hose in very poor condition. I am not sure yet if it is leaking there but it will fall apart if I wiggle it very much. Take a look here at about 3:40:
So tomorrow I will try a couple of things. First thing will be to run the truck until it reaches normal temperature. Then I will turn the temperature control to hot. Next I will manually move the blend door actuator rod by hand to see if I can get proper heat in the truck. If I can get proper heat, I will see what I can do to fix the blend door issue. It will defrost somewhat with proper heat, even if the mode controller is faulty. If I still can't get heat, I will try flushing the heater core again.
Additionally, I will replace the vacuum hoses that are obviously bad. If when replacing the hose I find oil in the lines, I know oil has been drawn at least up to that point and probably further. I could probably disconnect the vacuum switch at the transfer case and blow compressed air through and see if I could eject some oil. However, my guess is that oil already damaged the HVAC control and one or more actuators.