‘86 heater problem

[everettfirstlove]

I have a 1986 Chevy K 10 with a 400 small block and what looks to be a new heater. There is a line running off of the carb into a part on the firewall appears to be the vacuum but when I drove it today the heater would no longer work. It did this the other day, and I pulled the fuse put it back in, and it turned right back on, but today I went to the truck and turned the vent and the heater on on max and yet there was nothing. I don’t think the truck has to warm up for it to start. I just wanna know what the problem is and I’m already going to put a new unit in it for AC so what would y’all recommend and if I was to replace the control unit on the dash. Which one?

 

[83Stepper]

Going to need to know some more info friend. Sounds more like a power issue vs a heater plumbing issue. Can you hear the fan running? Is there no heat coming from the vents? Can you hear the actuator moving the door for the selector and heat?
If it's an issue with the fan not running, I'd start with the relay on the ac box. Make sure you're getting power there and that you've got power coming back out. Generally it's usually just a relay issue.

 

[everettfirstlove]

Fan doesn’t cut on at all, or is stuck on low, where is the relay?

 

[75gmck25]

Is this an A/C truck? You need to troubleshoot the heater blower motor a little differently.
On most years of these trucks, the lower blower speeds run through the dash switch and a resistor pack, but max/high speed runs through a separate fuse and the relay on the plenum under the hood. Have you lost the lower motor speeds or the max speed?

 

[everettfirstlove]

Is this an A/C truck? You need to troubleshoot the heater blower motor a little differently.
On most years of these trucks, the lower blower speeds run through the dash switch and a resistor pack, but max/high speed runs through a separate fuse and the relay on the plenum under the hood. Have you lost the lower motor speeds or the max speed?

It is a ac truck and has no blower noted at all but it has new motor so I think it’s a fuse or relay somewhere