My truck doesn't have AC but I just got an entire cab from a JY a few weeks ago, that
truck DID have AC and I stripped just about everything out of the thing so they wouldn't
charge me for it.

The non-AC heater core box is gonna require a bit of fabbing to make work in the
AC-equipped cab, the holes for the heater hoses are in a different place + there's a large,
rectangular hole in the firewall of the AC truck right around the antenna area, I'm
guessing this is where the AC coil is.

There may be other differences, too, this is just what I noticed out in the yard.

Pulling out the stuff inside the cab was surprisingly easy; I don't remember for certain but
IIRC there are only a handful of (metric) bolts holding the assembly on (which also hold
the engine side stuff on) , everything can then be pulled off the firewall (double-sided
foam tape as a gasket is gonna want to keep it in place.

I did all this with the entire dash - supporting structure and all - already removed, I figure
it'd kinda suck to do with the dash in place. You'd want to remove the glove
compartment box (removing the door, too, would make things easier), the radio & HVAC
controls in the center, I'll also suggest removing the top dash pad to have easier access
to everything.

If it were me, I'd rather fix the AC and make it work than remove it.

Your heater core should come out fairly easily if you wanna check for leaves & stuff
between the fins.

BTW another thing I noticed about AC-equipped trucks, there are holes in the bottom of
the cab near the kick panels, they kinda look big enough to maybe stick your hand in so
trash and stuff can be pulled out. There are rubber, um, devices kind of like covers on the
holes but they're split in the middle and can open up.

 

Yea, if I can easily remove the evaporator cover where I can inspect it/clean it, I might be more inclined to try to make the a/c system work at a later time.

I'll take a look at it in more detail later this week. If anyone has any tips, please share. I can use all the help I can get...

Oh, I just wanted to check my assumptions here. The blower DOES blow through the evaporator to get to the heater core, right? I didn't see any kind of bypass straight to the heater core when I had the blower motor removed.

 

I have no idea about the airflow but I'd be kinda surprised if it went across both to get at
only one, you'd think that would be too restrictive.

 

It's not uncommon in commercial RTU's

 

RTU?<table id="ListResults" cellpadding="2" cellspacing="0"><tbody><tr class="odd"><td nowrap="nowrap" width="60">
</td><td>
</td></tr></tbody></table>Régulation du Trafic Urbain (French: Urban Traffic Control)

 

Commercial Roof Top heating/cooling Units.

These are the big boxes you see up there.

As long as the coil is clean there should not be any loss of flow.

 

Sometimes I wonder about my haphazard diagnostics skills, but I think I'm making progress.

I cleaned out the kick panel that the blower draws it's air from, and tried heat again. No increase in air volume, but I did something different that might point to the problem better.

I don't use the a/c because there is no charge in the system. But sitting there, I put the controls to max a/c, and moved the heat selector to cool, and it blows up a windstorm in the truck. Moved the a/c selector to norm, and volume drops just a bit as it's supposed to.

Moved the heat selector to hot, and volume dropped through the floor, and I'm still not getting directional control.

Does this help spark some ideas as to where to look next?

Sorry to be a pest here, but I'd really like to get this system to work again. Thanks bunches!!!!

 

Watch what the little vacuum motors do as you move the HVAC levers, see if you can
see something that "doesn't look right." I have heard of broken hinges in some of those
assemblies but can't recall exactly which ones.

Do an Advanced Search and search for "piano hinge" WITH QUOTES and search only
in this forum, there should be a few threads you can read for possible help.

 

I am not good and troubleshooting this system either, but I can add a experience I had with my 1980.

It was a A/C truck, and someone had hacksawed the refrig lines off the evaporator coil. I wanted to put A/C in the truck, so I got a whole system from a old Ford car, and installed it in the truck. I took the box apart from the engine compartment side. There where a few bolts if I remember that had to be taken out from the inside of the cab, and then I split the box.

The original evaporator coil was almost totally clogged. It sweats when the A/C is working, and the dirt stuck to it and turned to mud and then hardened. Also when I got the coil out, there was a passageway into the cab, and there was all sorts of pencils, and debris in there.

After I cleaned all that out, and installed the other evaporator, I could not believe the difference in the airflow and heat from this truck. I can tell anyone who has a 80-up truck, the heater will flat run you out of the cab if it's in good working order, even on the coldest days.

P.S. The heater airflow does go through the A/C evaporator. They actually turn the A/C on when you are in defrost to dry the air out going to the windshield. It will defog the windshield twice as fast if the A/C is working.

 

Found the problem.

Took the heater core cover off, and looked into the passages to the left. I worked the heat selector lever, and saw that the selector door opened and closed just fine. What I also noticed was another tin door that seemed to be all wonked out...the one that seems to divert to the dash vents.

Sure enough, I worked the vacuum switch that selects vent/floor/defrost. When selected to vent, the vacuum motor pushes the door and diverts the hot air forward to the vents. But when selecting floor or defrost, the vacuum motor tries to pull the door forward, and at that point the door kicks out and get's jammed up all wonkey like.

Can this be fixed? (easily, without taking the whole cab apart???)

 

Sorry for the bump. Forum acted like it hung when I posted this, so I wasn't sure if it marked this thread as "new".

 

Sounds like the hinge is broken off.

Here's a diagram on the system I found:

 

Fixed for now. Took some duct tape and sealed the panel door shut for now, so at least I have good defrost/floor heat operation.

Got some GREAT diagrams from Eddie that will give me what I need for a spring project. I'll fix the hinge on the panel door, and go through all the ductwork and replace the seals then. Might even get the AC working. Never hurts to aim high, right?

Thanks again, guys (and gals)

 

Just wanted to make sure that all the diagrams I received on this issue were reposted in their full size.

Thanks Eddie!

 

Here's the wireing diagram for the blower and AC clutch.