87 Celebrity Vent Blend door

[EternalArianne]

The vent blend door intermittently works but most times it?s stuck on defrost. If I move the slider back and forth it will sometimes move to the front facing vents or the floor, or a mixture of all of them. It will switch between hot and cold fine, as well as fan speed control works. It?s only the blend door that is messed up.

Would this be the blend door actuator itself, or the actual control module with the sliders?

[tlc1976]

As I stated in the other thread, this can be caused by a vacuum leak. Mine was the purple hose from behind the engine to the firewall. Got really brittle and cracked. This could be causing some of your other problems too. If there?s no vacuum it will default to defrost.

[EternalArianne]

I think I see what you are talking about. I thought it was a red wire, but it is coming off the vacuum splitter above the manifold and it goes into a wire harness on the firewall. I didn?t find any vacuum leaks under the hood, could it be in the dash somewhere? Where would be a good place to start looking? I really don?t want to take the dash apart...

[tlc1976]

You should be able to remove the glove box and access a lot of things. Just open it and squeeze it and it will hinge way down. You can make sure the ECM connectors are fully seated too.

My purple hose was fine inside the car. Under the hood it was all cooked and brittle from engine heat and had broken in the loom of stuff at the firewall. I just replaced it with another vacuum hose and connectors.

[Pontiac6ksteawd]

Theres a check valve on the engine side of the vacuum hose. So it may not be detectable as a vacuum leak, but its likely there.

Kind of a pain to see and get to as well. Its usually right in the dead center, coming off the rear of the intake plenum.

[EternalArianne]

Yeah I see that check valve, it?s kinda like a splitter with a bulb on it. I?m going to pull the glove box out soon and check for a break/leak in the dash as well

[EternalArianne]

Ok I managed to check inside the dash, all the vacuum lines look good there, no leaks.

But I am wondering if maybe Im just not used to these older cars and how they operate the climate controls. I?ve noticed that if I set it to ?vent? it will blow air from the front vents. If I set it to ?defrost?, it will blow on the windshield. But if I set it to ?heat?, it will blow only on the floor.

The A/C side seems to blow from the front vents only, unless I set it to bi-level then it will blow on the floor and front vents. But I?ve noticed the fan seems to blow stronger on A/C vs heat, not sure what that means, if anything.

[tlc1976]

Sounds like it?s fine. If a vacuum line was bad it would be stuck blowing on the windshield no matter what.

I?m not totally familiar with the series of blend doors between the modes. Max AC I believe is supposed to recirculate which might blow stronger. My only A body with working AC is my Celebrity, and something is messed up with the blend doors where heat puts the air properly, but cold puts it on the windshield only. It changes as instantly as you can flip the heat/cold lever, much faster than it takes for vacuum doors to actuate. Being in Michigan I don?t even really need AC, so I?ve never taken the time to tear the dash apart and fix it.

[EternalArianne]

Yeah my neighbor said his 88 caddy behaves the same way so I?m guessing that?s just how old cars handled climate control - heat on the floor and AC in the face. I?m used to newer cars where you can control where it blows lol

[Keiths1976]

Actually there is a pressure storage tank on the front passengers fender near the bumper that the pink line runs to first then builds the pressure needed for the havoc system feeds over to the intake manifold filter then to the firewall harness inside the car for the switch assembly at least the 87 Pontiac 6000 ,90 Buick century and 95 Buick century since all a bodies km sure the celebrity is the same design

[tlc1976]

Yes I haven?t used ac in so long but I think max ac is recirculating in the face. Norm is ac outside air in the face. Bi level is ac outside air at different levels like you said. Defrost is ac at the windshield. Heat is air on the floor. Vent is air in the face. Any of these modes you control the temperature of the air with the temperature slider. Ac acts as a dehumidifier as well as a cooler, so if you wish you can have warm ac. Maybe for a warm wet climate.

[tlc1976]

Actually there is a pressure storage tank on the front passengers fender near the bumper that the pink line runs to first then builds the pressure needed for the havoc system feeds over to the intake manifold filter then to the firewall harness inside the car for the switch assembly at least the 87 Pontiac 6000 ,90 Buick century and 95 Buick century since all a bodies km sure the celebrity is the same design

You talking about the vacuum storage tank? I call it the blimp. I?ll have to check that out when the snow goes away. My pink or purple line runs right from the check valve behind the manifold to the firewall. But it doesn?t work quite right either. I thought it was just a storage tank for the general vacuum system of the engine.

[Keiths1976]

Yup that lines cracks over time and causes a loss of vacuum to the hvac system and hence you loose your vents . Mine cracked not long ago and lost all but defroster only . Had a weird idle blip . The port off the intake manifold runs first into the firewall harness cause u will see it runs to the firewall but there is a line runs up from that tank and stores the supply air

[Pontiac6ksteawd]

Actually, the "blimp", or air vacuum storage tank, is so that you can run WOT (wide open throttle) and not loose vacuum, thanks to those 1 way check valves. When you run WOT, your engine is not creating vacuum, but there are still elements of the engine that need vacuum (EGR Valve, HVAC, MAP, Transmissions, etc). That tank allows for a small amount of vacuum to be stored until WOT is over.

@Keiths1976 is correct, that these plastic lines, that run from the tank, and including the plastic tank, and plastic lines all over the engine bay (Cruise Control, EGR, FPR, Transmission, HVAC, etc), break down, crack, and some times just plainly disappear.

I recently sold a 93 Chevy Corsica 3100 that the vacuum lines coming from the check valve, and going the long way around to the transmission modulator, about half of the line was completely missing. It looked like battery acid (as the line did wrap around the battery) had just ate it away. Replaced the section of line with standard rubber vacuum line, problem fixed! But the open end created NO VACUUM. So I had no dash vents, no cruise control, check engine codes because the FPR was not working right, etc.

[EternalArianne]

Small update I think the control module might be a little wonky sometimes I flip it to Heat and stays on either the front facing vents or defrost (or both). At times it feels like it?s coming from all the vents at once (floor, front, and defrost). Same thing with the AC.

Sometimes if I move it to Off then back over to Heat it will rectify. It doesnt happen all the time, which makes me think it?s the control module itself.