Heater Help

[blacks197]

The truck is an '85 720 KC. Im having problems with the heater, i get nothing from the blower motor when i move the speed selector. Ive checked everything i can think of( new fuse,new relay,checked the switch,checked the resistor and even got a new blower motor). Is there something im missing? Any help would be great as driving this truck with no heater SUCKS

[thebigman]

how did you check the swith and have you checked the ground? mine did the same thing and one of the solder points on the switch popped of and i had to solder it back on

[breadbox]

Anything else wrong with it other than not blowing heat? Sure your heater core isn't clogged?

[blacks197]

bigman- my sister who is an electrical engineer checked the switch with her multimeter and said it looked good. Where is the ground for the heater?

bread- Im not sure about the heater core i cant even get the blower motor to come on so im not sure

[thebigman]

well i believe its the blue wire off the motor to test it unplug it and put a jumper to a ground and try turning it on

[blacks197]

Ok thanks ill try that when i get off work. Thanks

[blacks197]

Ok so i ran a jumper wire from the blue wire on the blower motor to a good ground still nothing

[thebigman]

did you test the motor before you put it in?

[blacks197]

Yeah i tested it right off the battery real quick and it spun good with no noise

[thebigman]

you check wiring cause it might be all hooked up but there might bu a short

[blacks197]

Yeah i think im gonna have to pull the dash out and trace it all the way back to the fuse panel. Not what i wanted to do. I was hoping i just missed something simple

[86 720]

Why do all that tracing when the battery is so close? Go buy a 6 position fuse holder from autozone, place it next to the firewall on the passenger side and run new wires to the blower fan on the otherside of the firewall. Now you got nothing to trace, and you have a bunch of spares for fog, lights and accessories.

[dogred]

Start at the fuse panel check for incoming power. Next check for power at the relay. The switch only applies a ground to the circuit. How many connectors are on your resistor?

The resistor just adds resistance to the circuit, so the more resistance the slower the motor will run, this is what actually changes your fan speed.

(This is out of my manual for a 1983 model)
Set your fan switch to high and check continuity from the black wire to the blue wire. Then check continuity through the harness from the switch plug to the harness plug for the resistor, Blue wire. If that is good check the rest of the switch plug wires the same to the resistor.

[mattthruwalkin]

my heater was working fine then one day the wife was driving it and the heater stop (my truck does not like the female sex) soooo i looked down by the fuse box , checked fuse was good , started poking and wiggling the blue heater relay and the heater would start working and stop when i let go if it , loose wire behind the fuse box ???? take the 2 screws out of the fuse block on the drivers side next to the clutch and start jiggling wires and relays and have the heater on 1 or 2 speed my 3 or high speed setting never has worked since i had the truck 3-4 years now

[dreadsiren]

I had problems just solved them though, replaced switch (visual inspection of solder points usually plenty) replaced relay (blue, first relay above fuse box under dash driver side) replaced motor, connected good harness (with zero splices)and checked all wires (single ground under dash, the switch and 2 wire to motor) replaced resistor (left of motor) and yes they were all shot, lmao! but still nothing... turned out the fuse box was not making proper contact with fuse (#7 fuse, 15a), cleaned contacts and re-gaped them (they were too far open) and now I have heat so even on a seemingly flawless harness there are always hidden little things, like a gap to large in the fuse connector

[Davezilla]

Glad this subject was brought up because mine has the same problem where nothing works at the switch. Here's what fixed mine after reading the other replies... Grounded the blue wire and the motor ran fine and also nice and quiet. That's all good but I want the fan speed control to work so I looked at the switch it's self and tested the ground point to all the other points inside the switch to no avail. Next I took a test lead and clipped it onto the black wire at the switch and grounded the other side, put the switch back together and now everything works as it should. Now I just need to find where the black wire goes to on the other side of the harness and fix the ground properly on that side to permanently fix it. One other bonus is that the AC still works but it's low on freon so I'll convert it over to run the R 134 before it starts getting hot over here.

[pistolkeith]

i have heater issues also. went to get it checked out(well, got the girl to go. you know, batter those eye lids ). dude said it was probably the core. i get the fan blowing when i switch it to heat. and i get air if i need it. however it is cold, all i want is to not have to drive wearing my down parka in the truck everywhere! so, my question to you genius's is how do i get to the core to replace it? and is it an easy replace for me; the incompetent foreigner whos slowly learning the lingo.

[86 720]

The heater core is not easy to get to. Get a Haynes manual, and follow the steps, replace the hoses while you're in there.