Heater system description - full size

[brinky]

I have a recently-purchased 1992 K5, and the heater is not putting out any heat. The radiator is full and seems to be working just fine; after the truck is warmed up, the hoses get hot, but it doesn't seem to be flowing through the core, or some such. Also, the dash fan control is confusing, at best. If someone could tell me if there's any electronic control on the heater core lines (would have to be hidden at back of block), and describe the correct functioning of the fan controls, I'd appreciate it.

 

[brinky]

Ok, I'll elaborate a bit on what I'm asking for....
1) How does the fan system work? It seems to me that the A/C works fine, but in order to get the fan to even blow, the A/C has to be on. In other words, is there a way to turn on the blower without turning on the A/C also? Do you specifically have to select the A/C off just to get heat?

2) Are there any in-line controls on the coolant flow to the heater core?

Thanks! Hope to be warm in my truck soooon!

 

[diesel4me]

heater valve..

What setting is needed to get heat?..I'd assume "A/C OFF" would switch it to the heat position..but none of my GM trucks have had factory air,so I'm not sure about that..all my non A/C trucks say "hot" and "cold" on the heater controls..

Some trucks with A/C had a hot water shut off valve in one of the heater hoses,9might be screwed into the intake manifold on some models)--it's controlled by vacuum from the heater control..if it fails or gets clogged up,or no vacuum gets there to activate it,little or no hot water will make it into the heater core..

 

[badmix]

First, why would you leave it on A/C to even get heat? seems kinda silly IMO>

Now when you try to defrost, I know that the A/C is involved. Here is what i would do

Turn the A/C off.

Turn the heat control to HOttest setting

Turn other controller to VENT.

Turn fan up High.

Make sure motor is warmed up, etc.

See what that does for ya.

 

[brinky]

diesel4me - thanks for the info on the control valve possibility! However, after inspecting the system thoroughly yesterday, I discovered there's nothing at all except plain hose to the core. But, in all the PO's wisdom, apparently a thermostat wasn't a necessity, so I've since installed one. After installing the thermostat (and new radiator cap) and warming the engine up until the water flowed through the thermostat, I still can't get any heat through the heater system. I did check the hoses, and they were warm.

badmix - I couldn't figure out why the A/C always kicked on until I checked out the control head for the "climate control", and I figured out how to get the fan running without the A/C engaged. However, it still doesn't blow any warm air. The way it works is you select which function you want with the two toggle switches, then the A/C will come on automatically, then push the "off" button, which turns off the A/C, (you see the status in the little LED window) but the fan is still running for you. Then you can adjust the fan speed with the "+/-" fan switch. There's no other way to get the fan running.

All of this works, but still no hot air. I have relegated myself to disassembling the heater box as the last resort - apparently the air mixture isn't being adjusted properly down there. The only other thing I can think of is the heater core is blocked, but since the hoses did warm up after installing the thermostat, I think that's unlikely.

 

[badmix]

Ya gots me then.

 

[fatbob]

I believe the damper or vent doors are vacuum controlled. And I also remember reading a thread a long time ago, about how a plastic clip on the door is prone to breaking. So crawl under there and see if the doors are moving while you play with the controls. You will need the engine running to supply the vacuum of course. If I remember correctly the best fix for the broken clip, was to make one out of thin metal.
Sorry I cant give more detailed info, but at least you know what to look for now.
good luck
Bob