Heater question

[Magic1]

Got a question about the head unit for my heater. I'm rewiring my 82 Sierra and the head unit for the heater was broke and the truck originally came with ac but it has long been removed so instead of replacing all the ac components I decided to just get a replacement head unit with heat only. My question is the original head unit has a blower speed switch, a selector switch for the various settings such as defrost vent etc, and a vacuum switch. Well, the new head unit only has the blower speed switch and no vacuum switch or connector for the defrost and vent settings. I'm assuming that it is supposed to have a connector for those which ill have to find because the one on my original unit doesn't fit the new one. Does the new one need the vacuum switch or is just for ac. The vacuum hose in the truck isn't hooked up so I'm not even sure what it does or where it connects. If anyone has any info please let me know cause I'm kinda stuck at this point and ill be very glad to have this freakin wiring job done!

[zieg85]

The AC style uses vacuum to operate the vents/floor/defrost while the non-AC unit only uses cables to operate it.

[Magic1]

The AC style uses vacuum to operate the vents/floor/defrost while the non-AC unit only uses cables to operate it.

Ok. Cable or cables. When I pulled out the old unit it had a cable hooked to the temp switch. What about the selector for heat and defrost?  The new unit has off/heat/defrost on the top section and cold/hot on the bottom. If the cable hooks back up to the temp switch I can understand that but as far as the upper switch, there's nothing on the back to make any electrical connections. Am I missing a part that goes on the back?  I assumed when I ordered it it would come ready to install but don't think so now. After looking at it I thought I would have to remove the ac rotary switch off the old one and put it on the new one but it doesn't fit. And if I'm using heat only does that mean I won't need that vacuum hose at all?  I'm lost. Lol. I guess what I'm wondering is what else I need to get it installed that the truck doesn't have now?

[zieg85]

Non-AC has 1 electrical connection to operate the fan.  The AC type has and additional one to turn on the AC when called for, see pic.  Both use a cable to open and close the door for heat/cold. (bottom slider).  Picture is one from a 91 Suburban dash I cut out and is in my parts stash.  Just to the right is the vacuum connection that operates the vents/defrost/heat

[Magic1]

Non-AC has 1 electrical connection to operate the fan.  The AC type has and additional one to turn on the AC when called for, see pic.  Both use a cable to open and close the door for heat/cold. (bottom slider).  Picture is one from a 91 Suburban dash I cut out and is in my parts stash.  Just to the right is the vacuum connection that operates the vents/defrost/heat

Yeah. The one you show in the pics looks identical to the one I pulled out of my truck. I'm just trying to figure out now how to hook up that middle connection and what to do with that vacuum hose. That middle connection is what my new head unit is missing along with that vacuum connection. All it has is the blower switch terminals on the far left

[Magic1]

Could anybody post some pics of a heat only unit so I could see what the back and all the electrical connections look like? That would help me out a lot!

[Magic1]

Ok. After looking into this on the Internet and talking to a friend that's a mechanic, I'm thinking maybe I have the wrong head unit. He says that the older style uses cables only for the defrost etc but since my truck uses the vacuum hose for the defrost and such, I'm gonna have to have a head unit which uses the vacuum connection to switch between defrost, vent etc. Am I correct on this and does it look like I have got the wrong head unit. I've pretty much got this thing rewired minus getting this heater working and figuring out the new gauge cluster which is another problem in itself.

[zieg85]

If you want your defrost/floor/vent to work you are going to have to get the AC type with the vacuum
operated controls.

[Magic1]

If you want your defrost/floor/vent to work you are going to have to get the AC type with the vacuum
operated controls.

Thanks bud. That clears things up cause I couldn't figure out how that new unit was gonna work but now I think I did get the wrong one.