Cold air at my feet and not to much in my face. Also no defrost...WTF

1986_GMC C2500 · Jun 5, 2024

What could be the problem as to why I'm having this issue. Turn my AC and majority of the cold air is at my feet. Also nothing comes out when I put it in defrost. Any ideas before I start tearing everything apart.

1lejohn · Jun 5, 2024

When my truck had the same problem the AC control unit wasn't getting any vacuum to the switch. I would start with pulling the control unit out and checking that you have a good vacuum source to the switch. If you do have good vacuum at the switch, then you will need to trace out the lines and make sure the vacuum motors are working properly. They are the rubber diaphragm's that operate the doors on the Heater/AC housing. There are 4 of them if I remember. There's one outside under the cowling, one on the passenger side floor kick panel, and 2 under the dash. If you do a search there are some good diagrams here on the site.

WFO · Jun 5, 2024

First, I'd make sure you're hooked up to vacuum at the carb or intake manifold.
Then it should go straight back to a tee at the firewall. One side goes to a round plastic canister that holds reserve vacuum, and the opposite side goes past the engine, and enters through the firewall before the AC/heater box.

1lejohn · Jun 5, 2024

Thats a good point. Mine was cut in the engine bay. I had to run a new line through the fire wall. I also had some leaks with the plastic switching valve on the controller. This was after connecting the new vacuum line.

Rusty Nail · Jun 5, 2024

I bet your feets are happy though!

Y'all aren't talking about fhat hard AF to set- plastic two dollar clippy that pulls the blend door open??

You can buy em but it's a pain in the effing a$$.

75gmck25 · Jun 5, 2024

It is unlikely to be the blend door, but it's also a good place to check. Blend door problems usually mean poor control of heat vs. A/C because that door is what determines whether the air flow goes through the heater core or the A/C evaporator.

This is probably an issue with engine vacuum supply to the controls, or maybe a cut hose up in the dash. When there is no vacuum applied to the vacuum motors, there are at least two vacuum motors/doors that go into an in-between setting that gives you mostly floor air flow, along with some defrost.

1lejohn · Jun 5, 2024

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YakkoWarner · Jun 6, 2024

I had the same problem when I first got mine so I'm betting on the vacuum line to be the issue. The hard plastic vacuum line had broken right where it goes into the firewall from the engine compartment - there was enough of a stub to sneak a small rubber vauum hose onto and make the connection back to the T at the intake. If I recall correctly the blend door is actually cable operated, the vacuum controls operate the diverter flaps that route the airflow from floor to dash vents to defogger vents.

Rusty Nail · Jun 23, 2024

Just tell me it was the 2 dollar clippy...where this guy go??

1986_GMC C2500 · Oct 24, 2024

Thanks guys
Found the problem and it's the small door that is broken at the hinge. Didn't want to mess with it and just cabled tied it to close it. As well as connecting the vacuum line correctly on my carb. Now I can feel the cool air on my face with this Texas heat.

Cold air at my feet and not to much in my face. Also no defrost...WTF

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