our plow truck is an 85 f-600, 370 2bbl, allison auto. a little bigger than an f150 but the cab and heater ducts are the same.

our heat system isnt working, and all we really need is constant defrost. what vacuum motors need to be held in place?

i would like a diagram. the fan blows on high, but doesnt seem like any air is coming out of any vents.

also, only one of the hoses going to the heater core is warm. any ideas?? ive searched with no results. thanks!!

 

Some basics about the cooling/heating system. Both heater hoses should be running at nearly the same temp. This shows you have flow thru the heater core, in your case, its plugged up. Remove both hoses and back flush the system. You can either use air or a garden hose will suffice. The hose from the intake manifold is the heater inlet, the hose from the water pump is the normal outlet, this is the hose to presurize to run fluid in reverse direction.

Your air flow from the registers is controlled by the function selector, either by cable or by vacuum. At this point in time, get the coolant to flow thru the heater core so both hoses are hot or near the same temp. Get back to us.