Hey gang, do any of you have diagrams etc of the vacuum lines under the dash, and before i go to the extreme pain in the butt of tearing my dash apart i think it may be a good idea to have an idea what to look for, im having heater issues and i definately hear hissing behind the heater controls.

 

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Many apologies. My blazer is a 91 4wd 4dr 4.3 tbi

 

This should help out:


And this gives the logic of how each mode is attained:

 

Fantastic! soon as i get it finished i will post results

 

kyle those diagrams worked out well. I had to replace my heater core so while i was in there i checked things out, all vac lines i could see were in place. However, I have got mediocre heat at best, do you know if you can "bypass" or shut the fresh air door without peeling the dash out completely? We have had -20 degree weather so heat is vital and money is short so ANY ideas are welcome

 

How well did you bleed the system after you replaced the heater core?

Get the front passenger wheel up higher than the driver's side and run the truck with the rad cap off, adding coolant as necessary. You'll have to let the truck cool completely, then do it again - probably 2 or 3 times.

 

i only lost about 1/2 qt antifreeze when i swapped cores and added 3/4 gallon new AF after a couple of running/off cycles.

Could a vent/door from the A/C system be acting up? My family mechanic (son) seems to think that may be a concern. He would look himself but he's in Ohio and I'm in New Hampshire.