Next issue Heater air flow

My next issue is heater air flow. After installing the refurb engine temp gauge from Blue Truck Parts, engine is at operating temperature. I can tell inside the cab is getting warm. I have air flow in defrost mode, (enough I can feel the flow), but don't seem to have any air flow in mix or floor mode. The fan is noisy off and on while it's in operation.  The engine does not have an AC compressor on it. If I remember correctly, I had air flow in vent mode when I purchased the truck and drove it home. It was hot that morning and I had the vent windows all the way open & the heater in vent mode for air movement because the AC didn't work. I will attempt to drive the truck with another person to see of any air flows while it's moving.

We have a number of current threads going on this, and Gary is documenting his testing and improvements.

If you have a vacuum leak the climate controls will default to defrost.
A noisy fan usually means the bearings are worn or the grease has packed up.
Some people have drilled a hole in the bushing to add oil but the usual solution is to replace it for around $30
(that's what I did)

ArdWrknTrk wrote

We have a number of current threads going on this, and Gary is documenting his testing and improvements.

If you have a vacuum leak the climate controls will default to defrost.
A noisy fan usually means the bearings are worn or the grease has packed up.
Some people have drilled a hole in the bushing to add oil but the usual solution is to replace it for around $30
(that's what I did)

Yeah, I searched here and the net before I posted but didn't find anything specific to my issue. Thanks for Gary's testing. Once it stops raining, I can follow Gary's lead. When the controls are placed in mix or floor, I have no air flow thru the defroster vents.

Well, the "only have defrost" is a well known and documented issue.

Also if you don't have vacuum, the fresh air door by the passenger hood hinge won't close.

Look at the 3 port manifold on the center firewall/cowl just below the hood gasket.
Follow this into the cab.
Follow the tube from the vacuum motor on the plenum by the hinge.
If you find broken hard plastic lines splice them with a piece of rubber vacuum tube or tygon fuel line intended for small (weedwacker/blower) engines.
This is easily found in any big box  outdoor equipment aisle with the replacement sparkplugs and pull cords.

If you have a 'juice can' vacuum reservoir on the passenger inner fender, take it off and see if condensation has rusted a hole in the bottom.

The diverter door in the ductwork is known to come off/break it's hinge.
A member here (Chuske) makes a kit to fix this.
There's a thread and a link in the marketplace to that issue.

These are the most obvious things I can think of, off the top of my head.

ArdWrknTrk wrote

Well, the "only have defrost" is a well known and documented issue.

Also if you don't have vacuum, the fresh air door by the passenger hood hinge won't close.

Look at the 3 port manifold on the center firewall/cowl just below the hood gasket.
Follow this into the cab.
Follow the tube from the vacuum motor on the plenum by the hinge.
If you find broken hard plastic lines splice them with a piece of rubber vacuum tube or tygon fuel line intended for small (weedwacker/blower) engines.
This is easily found in any big box  outdoor equipment aisle with the replacement sparkplugs and pull cords.

If you have a 'juice can' vacuum reservoir on the passenger inner fender, take it off and see if condensation has rusted a hole in the bottom.

The diverter door in the ductwork is known to come off/break it's hinge.
A member here (Chuske) makes a kit to fix this.
There's a thread and a link in the marketplace to that issue.

These are the most obvious things I can think of, off the top of my head.

Removed the center panel cover, the radio, and glove box. All the vac pots can be operated by hand. Removed screws from heater controls and moved controls backwards. While fishing, I found the bottom lever, does not have a cable hooked to it to tell the pots what to do? Gotta do some fishing for the cable after I search for cable diagrams.

The cable (wire*) should go to the heater box behind the glove compartment

ArdWrknTrk wrote

The cable (wire*) should go to the heater box behind the glove compartment

The only cable connection I can see is on top of the heater box. It moves when I change from AC to heat. I can't see or feel where another cable would connect? I was able to get a photo of where the cable attaches to the heater controls.

if your truck is a factory air truck then I don't think that one gets a cable. the vacuum selector switch supersedes it and operates the damper servos instead.

Right.  The EVTM has a bit of an explanation: https://www.garysgaragemahal.com/ac-heater.html

CDLong wrote

ArdWrknTrk wrote

Well, the "only have defrost" is a well known and documented issue.

Also if you don't have vacuum, the fresh air door by the passenger hood hinge won't close.

Look at the 3 port manifold on the center firewall/cowl just below the hood gasket.
Follow this into the cab.
Follow the tube from the vacuum motor on the plenum by the hinge.
If you find broken hard plastic lines splice them with a piece of rubber vacuum tube or tygon fuel line intended for small (weedwacker/blower) engines.
This is easily found in any big box  outdoor equipment aisle with the replacement sparkplugs and pull cords.

If you have a 'juice can' vacuum reservoir on the passenger inner fender, take it off and see if condensation has rusted a hole in the bottom.

The diverter door in the ductwork is known to come off/break it's hinge.
A member here (Chuske) makes a kit to fix this.
There's a thread and a link in the marketplace to that issue.

These are the most obvious things I can think of, off the top of my head.

Removed the center panel cover, the radio, and glove box. All the vac pots can be operated by hand. Removed screws from heater controls and moved controls backwards. While fishing, I found the bottom lever, does not have a cable hooked to it to tell the pots what to do? Gotta do some fishing for the cable after I search for cable diagrams.

Also if you don't have vacuum, the fresh air door by the passenger hood hinge won't close. The door works correctly.

The vacuum manifold on the right side of the controller has an open port. Could that be my issue or is it a vent?

mat in tn wrote

if your truck is a factory air truck then I don't think that one gets a cable. the vacuum selector switch supersedes it and operates the damper servos instead.

Thank you sir. That explains why I couldn't find a anything to attach a cable to.

I don't see any open ports on the vacuum diagram, but I don't have an AC truck, so I may be missing something...

ArdWrknTrk wrote

I don't see any open ports on the vacuum diagram, but I don't have an AC truck, so I may be missing something...

Thanks Jim! I don't want to be taking things apart if I don't need to. As you know, there ain't a whole lotta room in there.

I'd bet the "open port" isn't drilled.  There are several things that stick out but aren't drilled, for whatever reason.

If you have a vacuum pump, like a Mityvac, you can put it on the line going into the cab and see if it hold vacuum - reasonably.  They aren't "tight" and do leak some.  Or you could start the engine and feel back there to see if there's a vacuum leak.

But if there isn't an extra vacuum line hanging back there then you don't have one off.

Gary Lewis wrote

I'd bet the "open port" isn't drilled.  There are several things that stick out but aren't drilled, for whatever reason.

If you have a vacuum pump, like a Mityvac, you can put it on the line going into the cab and see if it hold vacuum - reasonably.  They aren't "tight" and do leak some.  Or you could start the engine and feel back there to see if there's a vacuum leak.

But if there isn't an extra vacuum line hanging back there then you don't have one off.

Thanks Gary, I don't have a vac pump, but I will get one. 20 years in field artillery & tanks, the hearing ain't worth a darn.

i you can get a pic strait on or even at a better angle you will see that there are a couple sheet metal nuts that hold the clear vinyl manifold onto the switch body. they seem to be uncapped ports from the angle of your pic.

If you get a vacuum pump you can connect it to the vacuum tee, circled in yellow below.  Connect it in place of the hose coming in from the right in the picture and pump up vacuum.  It should hold fairly well, although it'll leak some, and let you test the system.

However, if it is leaking fast enough that you can't pump it up and get inside to find out where the problem is then take the connector apart that should be behind the glove box.  It has a hose coming from the tee and then one going out to the outside recirc motor - the two lines you see where I said "Where vacuum goes into and exits the cab" in the pic.  You can take the connector apart and put your vacuum pump on the one coming in and pump it up while you look for leaks.  But bear in mind that the other hose will now be a leak when you go to Max since that's when the outside recirc door is to close.

Gary Lewis wrote

If you get a vacuum pump you can connect it to the vacuum tee, circled in yellow below.  Connect it in place of the hose coming in from the right in the picture and pump up vacuum.  It should hold fairly well, although it'll leak some, and let you test the system.

However, if it is leaking fast enough that you can't pump it up and get inside to find out where the problem is then take the connector apart that should be behind the glove box.  It has a hose coming from the tee and then one going out to the outside recirc motor - the two lines you see where I said "Where vacuum goes into and exits the cab" in the pic.  You can take the connector apart and put your vacuum pump on the one coming in and pump it up while you look for leaks.  But bear in mind that the other hose will now be a leak when you go to Max since that's when the outside recirc door is to close.

The outside recirc door operates correctly.

if your outside door is working correctly when operated by the dash panel then you should be able to trust that all others are getting the same available vacuum when told. it is not unusual for the vacuum switch to have a bad circuit(s) from age though.