Heater Issues

Hi,
I have a 1988 110 V8 and have had troubles with my heater ever since I got it but now it's hot it's more of a problem, heater blows hot with the fan off and on cold or any other combination apart from fan on where is obviously even worse.
First problem is that with the fan off at speed it still blows hot air out of the vents (perished foam seals) but pulling it on cold rather than hot has no effect (always hot, fan on or off). Even if I did have new foam seals it would still blow out the windscreen demisters and heat the car further. The the problem is the fan only has on full blast or off, that's less of a problem but could it be related? (From looking around her that sounds like the resistor has gone?).
Thanks in advance for any help

Hi
Check your heater cables. There are 2 of theses. 1 for the heat the other closes the flap to prevent any air through.
Think the 1on top does the hot/cold

The flap for windscreen is on the dash unit. This opens& closes feet to screen

As above.
FYI, the matrix always has hot water running through it, the cab lever controls a simple flap in the heater box that either let's the hot air through or doesn't.
Removing the box complete and stripping it down to free/clean everything up and reseal it will be worth it. You can join the engines flow/return pipes together so you can still drive the truck whilst working on the heater.

Whip the heater out and just close the cooling loop. Mine was like this for a year whilst I overhauled mine. The resistor is behind the square panel with the pop rivers.

I have a spare (used) resistor somewhere and can check it if someone knows what resistance it should show?

Also a good time to treat any rot issues with the foot well beneath the heater unit.