Defroster not working

[84GMCSierra]

I'm having a problem with my defrosters. When I put the blower on, the air is only coming out of the larger door in the ductwork near the floor(1st pic).I cant tell if there is anything missing from the vacuum connection on the back of the control panel so maybe someone here can see anything missing(2nd and 3rd pic).I had the middle ductwork(4th pic) out earlier this year to clean it but put it back in the way it came out. There was a gap between the lower vertical piece and the horizontal piece that goes to the middle A/C vent, so I put metal tape over it. When I put the control lever on each setting, nothing happens, except air comin out of the bottom. Am I missing something somewhere? The tiny vacuum line near the firewall on the engine side was broken, so I put a brand new piece of vacuum line on it to connect the two together to make one line(last pic)

 

[SirRobyn0]

From what I can tell it looks like all the vacuum stuff is hooked up. Does this truck have A/C I assume it does based on the pics but checking anyway. If so will the heater switch from floor to vent? See if it's getting vacuum down to the box. Not sure I can be of much more help, but obviously you need to figure out if there is vacuum getting to the box. If yes then there is an issue with the box, if not the there is an issue in the vacuum system.

 

[84GMCSierra]

From what I can tell it looks like all the vacuum stuff is hooked up. Does this truck have A/C I assume it does based on the pics but checking anyway. If so will the heater switch from floor to vent? See if it's getting vacuum down to the box. Not sure I can be of much more help, but obviously you need to figure out if there is vacuum getting to the box. If yes then there is an issue with the box, if not the there is an issue in the vacuum system.

My truck does have AC but it has been out since I removed the compressor, accumulator etc to give the engine a really good degreasing in 2019. Defrosters used to work but not since I last tried them about a month or so ago. When I go through al the settings on the control panel, the only place air is coming out is the large door in the first picture. It won't switch from the floor to the defroster vents. The line in pic #7966 has been an issue since I got the truck. It was broken off very close to the firewall, so I put the piece of vacuum line on it to connect the piece together. I'll look at all the vacuum lines this weekend to see if I have another line somewhere that is off. Thanks for the info

 

[84GMCSierra]

Ok you all. Just tore everything apart(cowl panel and screen, and went through all the lines I can see, and replaced some vacuum lines going through a check valve, into the intake, and can't find anything off or broken. One thing I did notice is the lever that opens the large door(where I'm pointing) at the bottom of the heater box doesn't move with any operation. I can move it by hand, but it doesn't divert air up into the defroster ducts. Is it supposed to move when I move the lever on the control panel? I can also see 3 of the 4 what I call vacuum pots, and the lines to them look ok , but the one behind the heater box(#3) I cant see to check the vacuum line. Probably a dumb question, but how can I figure out if there is vacuum getting to the box? I'm not sure how to hook up a line somewhere to do this. Thanks guys/gals

 

[sidschev]

check the vacuum outside where it hooks up...

 

[84GMCSierra]

check the vacuum outside where it hooks up...

In the ball shaped contraption by the brake booster?
Or where the line goes into the dash by the AC box?

 

[sidschev]

both make sure you have vacuum there . there should be vacuum at each line . if not then theres yer problem. i just got mine all working.

 

[75gmck25]

As suggested, check that line under the hood for vacuum as it comes out of the ball, and then find the same line where it comes through under the dash and check it again. It’s probably the thin GM hard vacuum line. I always hate to cut it just for testing, but you can easily splice it again with a short section of 3/16” rubber vacuum line.

You should also buy or borrow one of the small hand vacuum pumps, just to facilitate troubleshooting. It works to pull vacuum and test the vacuum motors, and then when you want to do a tuneup it’s good to test your vacuum advance or check for vacuum leaks.

 

[84GMCSierra]

As suggested, check that line under the hood for vacuum as it comes out of the ball, and then find the same line where it comes through under the dash and check it again. It’s probably the thin GM hard vacuum line. I always hate to cut it just for testing, but you can easily splice it again with a short section of 3/16” rubber vacuum line.

You should also buy or borrow one of the small hand vacuum pumps, just to facilitate troubleshooting. It works to pull vacuum and test the vacuum motors, and then when you want to do a tuneup it’s good to test your vacuum advance or check for vacuum leaks.

Thanks guys. I appreciate the answers. I'll get a hand vacuum pump as well.

 

[84GMCSierra]

As suggested, check that line under the hood for vacuum as it comes out of the ball, and then find the same line where it comes through under the dash and check it again. It’s probably the thin GM hard vacuum line. I always hate to cut it just for testing, but you can easily splice it again with a short section of 3/16” rubber vacuum line.

You should also buy or borrow one of the small hand vacuum pumps, just to facilitate troubleshooting. It works to pull vacuum and test the vacuum motors, and then when you want to do a tuneup it’s good to test your vacuum advance or check for vacuum leaks.

My line there was broken so I put a new piece of 3/16" line over it to connect the 2 pieces. It's tight but wondering if it's not tight enough to seal. I read somewhere in these forums about using a piece of shrink tubing to fix the line as well

 

[75gmck25]

In my experience, that 3/16” rubber line works well for splicing the old hard line. It pulling vacuum, so it doesn’t take a lot to seal if the fit is tight.

 

[sidschev]

My line there was broken so I put a new piece of 3/16" line over it to connect the 2 pieces. It's tight but wondering if it's not tight enough to seal. I read somewhere in these forums about using a piece of shrink tubing to fix the line as well

Thats how i got my line to seal extra good was a piece of shrink tubing get it tight then slide the other tubing over it. makes for a nice tight seal