i have a 91 firebird formula 305 tbi...apparently the previous owner removed the heater from the car as u will see in the pix (i hope)...my issue is that i only have the defrost vents with air coming out...i cant seem to get vacuum to the control switch in the car...im trying to find my issue and i see all these hoses going into the same harness as the other hvac wires...i have no idea what the previous guy did with these things but maybe u can tell me...i cant seem to find vacuum issue...any help is appreciated

thanks

also what im showing u is one of the vacuum lines that im assuming is to my hvac control...somehow hooked up to another vacuum line...idk if this is where my issue is or what...

 

Ok, one hard line goes to the heater control valve on front pass side
the other one tees to port side vacuum and then goes to vacuum ball inside drivers fender, the it too tees to cruise control.
You will have to figure which hard line goes where. 50/50 CHANCE!

There should be two hard lines coming out of the main harness right where your hand is. One of them will control the dash/vent/defrost

 

ok...there is one that goes to drivers side...the other goes to a canister looking thing on the passenger side of the motor with a few bigger hoses on it. guessing thats the vacuum lines....when i go under the dash to see the hoses there...the violet one and the grey one go to a plug that then go to two black vacuum lines that im assuming are the ones under the hood. i should have vacuum on both of those lines or just one? im pretty sure i dont have any at all on either of them

 

If for some reason the issue is my check valve, will this one work? It says it universal

http://m.autozone.com/autozone-mobile/en/accessories/Help-Two-way-vacuum-check-valve/_/N-25hz?id=230927

 

The first pis is pointing to the line that connects to the check valve to the port plenum then tees to the vacuum ball on the drivers side fender

the second pic is going to the heater control valve

the universal check valve SHOULD work

 

if either hard line under the hood is NOT connected to anything, you will NOT have vacuum. You must pick up a vacuum source from the port plenum as shown in my post above.

 

Thanks for posting visceris and Bob, I had the same exact questions.....

 

Ok i just replaced the check valve as it was in three seperate pieces. Also replaced vacuum line that goes to the vacuum ball on drivers side with brand new line. Still have no vacuum at hvac controls. I do have vacuum at the vacuum ball near drivers headlight so i know there is vacuum in that circuit. Bob....that second pic u posted...when the engine is running and i pull that line...i have no vacuum at all there. Should i? Its dead...along with where it connects on that canister thing. Thanks all for your help. This is probably the most irritating project ive had so far.

 

Hang in there....you'll get it.
The second pic is the Heater control valve line. It will have vacuum with the engine running. If all the lines are hoohed up right, that would operate when you slide the temp lever to hot/or cold. It diverts hot coolant from flowing through the heater core.
The other line that goes under the dash to the controls( that comes from the ported vaccum at the tee at the check valve, only controls the flapper/damper for dash/defrost/floor vents. Its your main supply to the controls on the dash.
What you can do is get some loooong vacuum line and run from that check valve around through the pass. door and connect it to the control panel to see if those hard lines are broken in the wiring harness. Or, just run new lines through the firewall.
Just some ideas

 

ok...so as i mentioned in the first post my heater has apparently been removed...so i should not need that part of the system.

the vacuum line coming from the check valve going into the firewall is what controls the flapper things in the dash...so if i can get a new line to replace that i should be ok..i hope

also, if that does not do it...which one of the vacuum hoses goes into the dash to the flappers? could those be bad or dryrotted?

sorry for the rambling..and ty for help again

 

Your fine, no problem.
1 hard black line is SUPPLY to the controls; one is return or OUT. You may have to try both.
Follow this diagram and you should be golden

 

I believe the supply on the back of the controls is VIOLET

 

Im pretty sure u have just solved my issue. As i was heading to work i checked to see if there was vacuum at the line feeding the violet tube...none. So i go into engine bay and check it at other end where it goes to check valve. Boom...vacuum coming from check valve. I need the vacuum line that runs from the check valve through the firewall to the hvac controls. Do u kno what size that is? Does it have to be actual vacuum hose? I can guarantee my local autozone or whatver wont have it...since they never have anything else i need.

 

Just go to the parts store and make sure you get VACUUM LINE and not fuel line. That hard line inside diameter is like 1/8". So, don't be too concerned. Just make sure it slips on the other ports real snug. they have that in stock

 

Awesome. Thanks so much. Made my day =D

 

you bet, let me know how you made out.

I'm changing Wife's Laptop screen now. Going off line till tomorrow!

 

System is all fixed. Just for everyones info...the vacuum line that runs thru the dash is 1/8" outer diameter. Advance auto parts sells it in 3ft sections and u can get connector if u need it longer.

Also, can any1 point me in the direction of the r134-a retrofit kit? I cant find it. Would be nice to have that updated in the near future