Defrost not working

[rampage]

I’m trying to diagnose why my friend’s defrost isn’t working on his ‘84 truck. Hot air comes out the vents no matter if it’s set to vent or defrost. Thought for sure it’d be the white plastic clip was broken but it’s still intact. Not really hearing a vacuum leak but I might be listening in the wrong area. What would be the next and easiest thing to check?

 

[Wes Harden]

The defrost is suppose to be the default position. Maybe some debris is blocking the door. Or possibly is leaking into dash. The upper half of the defrost plenum fits over the lower, factory there is a foam gasket to fill the gap, probably disintegrated. mine was, is now got a wrap of gorilla tape around it.

 

[rampage]

The defrost is suppose to be the default position. Maybe some debris is blocking the door. Or possibly is leaking into dash. The upper half of the defrost plenum fits over the lower, factory there is a foam gasket to fill the gap, probably disintegrated. mine was, is now got a wrap of gorilla tape around it.

This gasket?

 

[Wes Harden]

yup that one

 

[rampage]

Looks fine to me.

 

[rampage]

But the defrost just suddenly stopped working. Wouldn’t it have stopped a while ago?

 

[rampage]

And no debris. I can manually operate the door and it closes relatively easily. I do hear a whoosh if that’s normal.

 

[Wes Harden]

you would think. Leads me to believe something fell in the defrost vents and has block a door

 

[Wes Harden]

 

[rampage]

Could it possibly be the actuator (part #30)?

 

[Wes Harden]

No vacuum or vent is defrost, on diaphragm 21

 

[rampage]

I posted while you were posting not sure if you caught that.

 

[Wes Harden]

I think 30 is hot cold door

 

[rampage]

Part 24 is the plastic clip that usually breaks and the diagram shows part 30 attaching to that clip and blend door if I’m not mistaken.

 

[Wes Harden]

yep blend to me means mixing hot and cool

 

[rampage]

Should I hear a whoosh when I manually operate the blend door?

 

[Wes Harden]

?

 

[rampage]

?

Sounds like it’s coming from the defrost actuator by the gas pedal (part 21)

 

[Wes Harden]

you hear air move from the vacuum actuator ? afaik the actuator vents at the rotary vacuum switch. Been a long long time since I could vacuum leaking any where.

 

[rampage]

Been while since I’ve messed with the heater/defrost stuff so I forgot how it all operates.
The diverted valve (part 27) isn’t closing all the way to block off the vents if that helps.