Hot air entering cab

[JavaMan]

I've been having issues with the AC not cooling well. Its a 96 Suburban K2500. But the pressures high and low are where they should be. I was checking to see if the blend door wasn't working right, I found hot engine air blowing into the cab right at the AC recirculation intake. Everything right around that foot well was warm or hot. I put a thermometer back there, its coming in at 145 degrees

Is this a common problem?
I haven't pulled everything apart yet, feels like its coming from behind the AC recirculating intake, blowing downwards.

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[96-2D-Hoe]

I've been having issues with the AC not cooling well. But the pressures high and low are where they should be. I was checking to see if the blend door wasn't working right, I found hot engine air blowing into the cab right at the AC recirculation intake. Everything right around that foot well was warm or hot. I put a thermometer back there, its coming in at 145 degrees

Is this a common problem?
I haven't pulled everything apart yet, feels like its coming from behind the AC recirculating intake, blowing downwards.

Sent from my SM-G965U using Tapatalk

My 96 K1500 has a heater control valve that is controlled by vacuum. When the AC is on the valve should be closed with no hot water coming into the cab. On my K1500 truck it's on the left side below the air cleaner housing. Two lines that run into the bottom of the firewall. There is a solenoid mounted on the firewall above to the right of the hoses that controls the vacuum.

I just replaced mine recently as it was leaking. And the vacuum line that controls it was completely perished. Never knew it was there before that.

Sounds like you may also have blend door issues but check the heater valve

 

[454cid]

Trucks don't normally have valves on the heater core lines, that was mainly an SUV thing..... if I ever get around to it, I've got a ball valve to install on mine, since I don't see the point of nearly 200F coolant circulating through my HVAC box in the summer.

I'd look at that blend door...... mine may also be going out, but I'm not driving the truck daily anymore, so it's super back burner.

 

[east302]

I've been having issues with the AC not cooling well. But the pressures high and low are where they should be. I was checking to see if the blend door wasn't working right, I found hot engine air blowing into the cab right at the AC recirculation intake. Everything right around that foot well was warm or hot. I put a thermometer back there, its coming in at 145 degrees

Is this a common problem?
I haven't pulled everything apart yet, feels like its coming from behind the AC recirculating intake, blowing downwards.

Sent from my SM-G965U using Tapatalk

See if the antenna grommet has come loose and is letting engine compartment air into the cab. It goes through the firewall in that area - kind of below and behind the bottom of the blower housing.


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[96-2D-Hoe]

if I ever get around to it, I've got a ball valve to install on mine, since I don't see the point of nearly 200F coolant circulating through my HVAC box in the summer.

The one for my 96 has connections for 5/8 and 3/4 ID hoses IIRC. It doesn't take a lot of vacuum to operate. Just FYI in case that helps your potential project.

 

[SUBURBAN5]

If it was mine look at the blender door. Also look at your evaporator coil and clean it of you haven't, good time to clean junk that falls in there.. and making sure nothing goofing going on in there. (not your cause) but you want that clean with your ac blowing in hot days. Mine is a "suv" so I have that t and vacuum line. I would check that like mentioned above..

 

[Schurkey]

Opposite problem, but I bet it's the same cause. Mine was on an '88 K1500.

I went crazy trying to get my cab to heat up in the winter. 30 miles of highway driving, with a new heater core and a 205 degree themostat...and I still had to wear a snowmobile suit to work.

The plastic heater / fan motor ducting is sealed to the stamped-steel cowl with foam gaskets. The same sort of foam seals are used in other places on the heater ductwork.

All the foam had turned to jelly. MASSIVE air leak from the cowl into the cab. In the winter, it's a cold-air leak. In the summer, it'd be a hot-air leak.

Had to tear the whole dash apart to replace the foam seals. I used ordinary weatherstripping foam from the local "home improvement" store--Lowe's, Home Depot, Menards, or even Ace Hardware. 1/8" X 3/4, I think. Might have been thicker--1/4", maybe. Closed-cell, adhesive-backed.

Photo 1--dash out, heater blower motor and housing removed

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Photo 2--Having the blower motor housing out gives you a good opportunity to pick the garbage out of the A/C evaporator.

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[kylesk1500]

@Schurkey Thanks for the pictures, detailing your problem and previous attempts to fix it. However I do have a couple questions. Were any other parts wore out because of the flap sticking, like one of the actuators or something?

And where specifically was the plastic heater / fan motor ducting sealed to the stamped-steel cowl with foam gaskets? Is it in the pic or on the plastic motor housing that connects to the evaporator case?

I'll be attempting this project this summer, being in a cold state like you, the leak is unbearable.

Thanks!!

 

[Schurkey]

The foam gasket that was causing my cold-air leak is "straight up" above the fan housing, where the steel of the cowl connects to the fan air intake.

 

[BigWaveDaveAZ]

My 96 K1500 has a heater control valve that is controlled by vacuum. When the AC is on the valve should be closed with no hot water coming into the cab. On my K1500 truck it's on the left side below the air cleaner housing. Two lines that run into the bottom of the firewall. There is a solenoid mounted on the firewall above to the right of the hoses that controls the vacuum.

I just replaced mine recently as it was leaking. And the vacuum line that controls it was completely perished. Never knew it was there before that.

Sounds like you may also have blend door issues but check the heater valve

I'm having the same problem. I'm looking for info for the vacuum lines that come from the firewall to the inline heater hose module. One vacuum hose goes to the control module and the other fitting on the firewall has no hose coming from it. I figure it has to go somewhere on the engine to get vacuum, but can't find where the hose connects to on engine.