806camaro

AC only blows out of the defroster vent, but when I hit some good bumps in the road, the air will come out to the vents facing the passengers, but when I turn off the car or turn off the AC, and proceed to turn it on again the is coming back out the defroster vents. Why is this, what is broken? Thanks for any input.

ASE doc

The vent modes are controlled by vacuum. I would first check for any disconnected lines either at the vacuum reservoir, or going into the harness at the firewall. It's a little hard plastic line. I have seen the vacuum control at the HVAC switch assembly come apart but this is rare.

806camaro

Thanks for reply, but where is the vacuum resevoir located and the harness located at on firewall?

ASE doc

On my 87, the reservoir is under the EVAP canister and accessible from under the car. The vacuum line goes into the harness just behind the distributor(as I remember). The Beasty is at home in the garage as the weather isn't great today so I'll have to wait til later to take a look later to be sure. The vacuum port for this is right beside the port for the fuel pressure regulator at the rear, passenger side of the plenum.

Dmans85

I'm having a similar issue. After recently putting the center console back in and jostling the radio and a/c assembly assemblies, I have the air flow stuck directing air through the windshield defrost vents.
Looking back behind the assembly I don't see a vacuum line. Just three wires behind the vent/a/c/defrost/htr slide assembly.
Where should I direct my attention?

toppgunn77511

i have the same problem a/c only blows out of defrost vent

Dmans85

Well sorry to hear you're in the same boat. I was able to look around some tonight but didn't come any closer. Post up if you have any leads

toppgunn77511

Well I turned the a/c to off position and turned the car off and then turned the car back on and turned a/c on and started working regular agian. Blowing normal out of the a/c vents now.

ASE doc

topgun, it sounds like you have a loose connection in the vacuum lines at the rear of the AC control unit. The vacuum lines are little nylon tubes that look alot like wires. They all intersect at the vacuum switch which, as I remember, is at the right end of the control as viewed from the front.

Everyone, the default position of the mode doors is defrost. With no vacuum supply, the system will always be in defrost mode. Vacuum is supplied to the HVAC system via a small black hard nylon tube that runs through the main harness. It breaks out of the harness just to the driver's side rear of the distributor. I could be backwards on the position, driver's or passenger side of the dist, but it's right there close either way. I just had my hood open this weekend cleaning and shining my engine but I forgot to look at the vacuum line. If you can't find it, it may be broken inside the harness, in which case you'll need to dig for it.

The typical test of the HVAC controls is to apply vacuum with a hand vacuum pump. The controls should hold vacuum in every position and, with the fan running, you should feel air coming from the selected vents. If this test fails, you need to find the leak in the control circuit. Logic dictates that if the leak is small and the system works with the engine running, who cares if it bleeds off after the engine is stopped.

EDIT: I forgot to mention the reservoir. There is a round(like a globe) reservoir under the purge canister. You need to access it from under the car. If it is broken or one of the lines is off from it, you will not have sufficient vacuum to the HVAC controls. You can check for this by testing for vacuum at the check valve where the hard black nylon tube connects. You will need a vacuum gauge to test for vacuum loss by comparing the reading to the vacuum at the plenum where the source line connects. You should have a vacuum diagram for the system, which you will find in any good workshop manual.

Damon

What ASE Doc said.

Be aware that although the SOURCE of the vacuum is a vacuum line at the rear/passenger side of the engine the vacuum line hits a "T" just beyond the one-way check valve near the firewall. One side of the T leads through the firewall via the main wiring harness to the HVAC selctor assy. The other side of the T goes to the vacuum reservoir inside the front of the driver's side fender (the softwall-sized plastic "death star" inside the inner fender).

So you need to make sure there are no horrendous leaks on EITHER leg of that T fitting. Since they are both on the HVAC side of the one way check valve a leak anywhere in the lines on either leg of the T will bleed vacuum and possibly cause the vent selctor to not work properly.

Dmans85

words of wisdom noted and will apply to best of ability. Those tubes do a good impersonation of wires

erik69&85

iTrader: (1)

Just a little adder...my 1985 Z, without AC, did not have vacuum control. All the doors were controlled by cable pulls. So if you don't have AC, its not a vacuum line.

ASE doc

Any of the cars with sliding temp controls had a cable operated blend door. It's the mode doors and the heater control valve that are vacuum operated. I'm not sure about the AC delete models. I'll take your word for it. All Data shows some cars in 85 also having electronic AC. These cars are different also as they have a solenoid controlled vacuum mode system.

Dmans85

Well at long last I finally went looking around today. As it turns out, it was something as simple.
I had fullly pulled away the group of 5 or so tubes that are in a cluster away from their male couterparts on the right rear of the AC slide assembly. Not knowing exactly how it is supposed to look I had to take the console out again for the umpteenth time. Then I saw the cluster that was all by itself.
I saw nothing holds that cluster in there exept a tight/snug fit. Are there supposed to be any clips or rubber doughnut type sliders to keep from doing what I did, and accidently pulling it (cluster of tubes) away from the unit?

BogusWarrior

I had the same problem with AC and heat coming out of the defrost, but would come out front vents when I hit a bump. I traced everything and couldn't find a leak. Out of dumb luck I noticed when I move the T valve that it would blow out the front vents, when it would blow out the defrost I just flip the T with my finger and it works correct again...bad valve! Better to be lucky than good.

806camaro

Where is this "T Valve" located at buddy?