please help! ac probs
Thread Starter
Racer
Joined: Nov 2006
Posts: 258
Likes: 1
From: Temple, TX
please help! ac probs
Alright so when I bought the car the guy said the ac worked which really meant that the heater was stuck in the on position and only blows out by the floorboards. I got the heater turned off by taking it to a mechanic and he used a manual valve to turn it off? then he said that I needed a new ac control unit. I bought a new unit off of ebay and installed it this morning. Now the low med and high work flawlessly but the ac still only blows out by the floorboards, can anyone help? is this a vaccuum leak? where should I look? thanks!
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
C3 air is controlled by vacuum- when you switch the control in the dash from MAX to DEF can you hear anything hissing? It's possible the source from the intake manifold is disconnected. (located usually at the same port the headlights get thier vacuum).
there is a vacuum valve on the control head too. With the connector removed, start the engine and check that one of the ports has good vacuum, then take a small hose and apply vacuum from that to the outer ports and see if doors move and re-direct the air.
Most of the factory manuals have good diagrams of the vacuum system. That will help get your troubleshooting figured out.
The water shut-off is vacuum controlled too- another clue to a vacuum related problem.
there is a vacuum valve on the control head too. With the connector removed, start the engine and check that one of the ports has good vacuum, then take a small hose and apply vacuum from that to the outer ports and see if doors move and re-direct the air.
Most of the factory manuals have good diagrams of the vacuum system. That will help get your troubleshooting figured out.
The water shut-off is vacuum controlled too- another clue to a vacuum related problem.
Last edited by TimAT; Aug 1, 2009 at 09:42 AM.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
I wrote this up awhile back for this problem.
On at least later C3 the problem is that heater is the default position (no vac. or vac. leak) due to being designed in the north. Vent should be default.
1) The vac. line from engine is damaged from heat - a small plastic tube that goes in below the hood alarm switch into wiper valley. Replacing most of engine side w/ hose will fix. OR
2) The vac. switch itself is not switching due to vac. leak as the usually plastic rivet is not holding the 2 main switch parts together well. Besides replacing, it is also possible to tighten this &/or lube w/ a thin layer of white lithium grease to fix.
3) If you have a heater, the small vac. tube to heater hose valve underhood probably also needs replacing. Block w/o heater.
PS The design problem comment is not intended to be offensive to any of our northern friends.
On at least later C3 the problem is that heater is the default position (no vac. or vac. leak) due to being designed in the north. Vent should be default.
1) The vac. line from engine is damaged from heat - a small plastic tube that goes in below the hood alarm switch into wiper valley. Replacing most of engine side w/ hose will fix. OR
2) The vac. switch itself is not switching due to vac. leak as the usually plastic rivet is not holding the 2 main switch parts together well. Besides replacing, it is also possible to tighten this &/or lube w/ a thin layer of white lithium grease to fix.
3) If you have a heater, the small vac. tube to heater hose valve underhood probably also needs replacing. Block w/o heater.
PS The design problem comment is not intended to be offensive to any of our northern friends.
Last edited by Ganey; Aug 1, 2009 at 10:25 AM. Reason: deleted 'or vasoline' to fix.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Good post Ganey- I'd recommend using KY instead of vaseline though. The vaseline, being petro based, will eventually kill the rubber/plastic stuff.
Thread Starter
Racer
Joined: Nov 2006
Posts: 258
Likes: 1
From: Temple, TX
ok I have found two hoses that are disconnected the first hooks up to the thermostat housing, the plastic piece is broken so guess I get to replace that.
Ganey-no.1 on your list.... that hose looks fine but where it connects in the engine bay there are two ports for vaccuum lines and it looks like one of those should go to the egr valve? that piece is broken off as well could either of those be causing the ac to not function?
Ganey-no.1 on your list.... that hose looks fine but where it connects in the engine bay there are two ports for vaccuum lines and it looks like one of those should go to the egr valve? that piece is broken off as well could either of those be causing the ac to not function?
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Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Ganey-no.1 on your list.... that hose looks fine but where it connects in the engine bay there are two ports for vaccuum lines and it looks like one of those should go to the egr valve? that piece is broken off as well could either of those be causing the ac to not function?
After that when testing, reving the engine which will increase vac. when the throttle closes may help get it going again. If not press the switch halves together w/ fingers.
Thread Starter
Racer
Joined: Nov 2006
Posts: 258
Likes: 1
From: Temple, TX
yeah I have seen a black chrome bumper running around and then I know another guy in belton its a nice area thanks... by the way I either hooked up all hoses or plugged them off and to no avail. Finally I just pulled out the whole dash and propped the door open for the top vents as a temporary fix. I would still like to know what it is exactly that opens that door? it seems like there is a spring trying to hold it shut? is the door vaccuum driven or is it mechanical? thanks guys!
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Doors are all vacuum that are spring loaded one way or the other. The vacuum plls them to the "alternate" position. You do have vacuum at the switch in the console? If not then it's either unhooked or broken under the hood.
Thread Starter
Racer
Joined: Nov 2006
Posts: 258
Likes: 1
From: Temple, TX
ok guys I know its been a little while but I found that one of my vac probs was the heater control valve, replaced it with a new unit and ran the vac line. ac will blow cold for about 3-4 min then start blowing really hot again guess its the door inside the dash, is this door on the driver or pass side?
Advanced
Joined: Aug 2009
Posts: 54
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Is there a way that you know of that I can permently close the flap/door at the squirrel gage to direct the air through the a/c vents. I just dicovered I have fiber glass damage on the inside of the finder where the flap/door bracket fasten to the finder.
By the way its a 79 L82 bought it a year ago.
wtbrs123
By the way its a 79 L82 bought it a year ago.
wtbrs123
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
Your distribution box has 2 flapper doors. One is the mode door (defrost, vent, floor) and the other is the temp door. Based on your HVAC settings these doors open and close either fully or partially.
Look at the box on the passenger side near the floor and center console. Operate your heat, A/C, temp thumb wheel. You should be able to hear, see and feel the doors moving as you change the selection. The doors are operated by a vacuum that moves a lever that moves the flap.
If the temp door or mode door are not moving, disconnect the vacuum supply line and apply your own vacuum to see if the doors will move. Also check the end of the vacuum line to see if you can feel a vacuum when you change modes or temps.
As mentioned you would then need to find out why it isn't getting any vacuum. If it is getting a vacuum maybe the door is stuck, the vacuum valve is defective or the mechanical lever is rusted.
Look at the box on the passenger side near the floor and center console. Operate your heat, A/C, temp thumb wheel. You should be able to hear, see and feel the doors moving as you change the selection. The doors are operated by a vacuum that moves a lever that moves the flap.
If the temp door or mode door are not moving, disconnect the vacuum supply line and apply your own vacuum to see if the doors will move. Also check the end of the vacuum line to see if you can feel a vacuum when you change modes or temps.
As mentioned you would then need to find out why it isn't getting any vacuum. If it is getting a vacuum maybe the door is stuck, the vacuum valve is defective or the mechanical lever is rusted.