91' XJ40 Air Conditioning
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From: Wisconsin
Is the black line from the engine?
There is a check valve in the engine compartment at the firewall where the line enters the cabin. Is that to maintain vacuum in the cabin when the engine vacuum is lower? Like on acceleration? I remember the vacuum operated wipers on my first car, a 55' Chevy...on trailing throttle they would speed up, and on acceleration they would almost stop!
GrandpaDan
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From: Wisconsin
Ok, well first thing to check is whether or not the cold air is being "sent" to the centre vent - (if that is what you mean by "face vent" -if no air from side vents too, different ball o'wax)
This test takes for granted that both of your blowers are running.
To check, pry off the wood trim at centre vent and remove the plastic grille/vent. If you peer in there with a flashlight with controls set at max cold and car fully warm you should see the vacuum flap open. If it's closed, get something like a chopstick and push it open. With it open you should get a blast of cold air. You can wedge it open to get face vent air temporarily til you figure out why it isn't operating with vacuum.
If the vacuum flap IS open and you don't get a blast of cold air, then something is preventing the upper blend door in the climate control unit (CC) from operating. That can be a couple of things, the main reasons are a broken demist flap falling down from the upper part of the dash into the heater and jamming the mechanism (common), a faulty motor on the side of the CC or a faulty/bad connection at the climate computer. The motors and the computer are mounted on the RH passenger side of the unit.
This test takes for granted that both of your blowers are running.
To check, pry off the wood trim at centre vent and remove the plastic grille/vent. If you peer in there with a flashlight with controls set at max cold and car fully warm you should see the vacuum flap open. If it's closed, get something like a chopstick and push it open. With it open you should get a blast of cold air. You can wedge it open to get face vent air temporarily til you figure out why it isn't operating with vacuum.
If the vacuum flap IS open and you don't get a blast of cold air, then something is preventing the upper blend door in the climate control unit (CC) from operating. That can be a couple of things, the main reasons are a broken demist flap falling down from the upper part of the dash into the heater and jamming the mechanism (common), a faulty motor on the side of the CC or a faulty/bad connection at the climate computer. The motors and the computer are mounted on the RH passenger side of the unit.
Both blowers are working, and there is good cold airflow from the side vents, but nothing from the "center" vent. It's cold in there, but very little airflow.
Would a check of the vacuum system be if the heater control valve is working, the lines are intact?
Do I use like a plastic trim tool to pry off the wood trim?
Thanks again. I'm optimistic that we can get this working.
GrandpaDan
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From: Victoria BC Canada
You can pry off the centre trim with anything handy, it's held in place by spring loaded push-clips and is very solid and robust.
It keeps the plastic diverters in place, once you get the trim off it's all pretty logical in there.
Sounds like the vacuum flap isn't opening and yes that's driven by a vacuum line to the valve. The flap is hinged at the top so if you push at the bottom it will open. If you want cold air at the centre vent, just wedge something in there to hold it open. After you find out what the issue is you can take the wedge out (or leave it in if you want warm air from there in the winter
) meanwhile, you'll get nice cold flow.
I would guess if you can get access to the vac line and use something like a Mitivac (or just suck) you can check the operation. Not had trouble with vacuum lines myself so no experience there, sorry.
It keeps the plastic diverters in place, once you get the trim off it's all pretty logical in there.
Sounds like the vacuum flap isn't opening and yes that's driven by a vacuum line to the valve. The flap is hinged at the top so if you push at the bottom it will open. If you want cold air at the centre vent, just wedge something in there to hold it open. After you find out what the issue is you can take the wedge out (or leave it in if you want warm air from there in the winter
) meanwhile, you'll get nice cold flow.I would guess if you can get access to the vac line and use something like a Mitivac (or just suck) you can check the operation. Not had trouble with vacuum lines myself so no experience there, sorry.
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From: Wisconsin
It all came apart just as you said, Lawrence.
I was confused about the "face" control, and thought it was just the center vent. Now I get it..."face vents" are the three vents at "face" level. If you are short, anyway!
So the center vent flap was shut, and nothing I did on the control panel changed that. The actuator that opens/closes the vent is easy to see with the grill out, and I traced the black vacuum tube out and opened it at a coupling and sucked on it, and the actuator operated fine.
This suggests to me that the vacuum solenoid is defective, has a bad connection/broken wire at the solenoid, or a bad connection at the microprocessor or a defective microprocessor. The wiring diagram shows one wire to the solenoid from the microprocessor, and a ground.
All very hard to see, as the connections are on the inside of the solenoid, and it's a jungle in there!
I have another microprocessor on hand, but I'd like to work from the solenoid back if I can.
Thanks for all the help!
GrandpaDan
I was confused about the "face" control, and thought it was just the center vent. Now I get it..."face vents" are the three vents at "face" level. If you are short, anyway!
So the center vent flap was shut, and nothing I did on the control panel changed that. The actuator that opens/closes the vent is easy to see with the grill out, and I traced the black vacuum tube out and opened it at a coupling and sucked on it, and the actuator operated fine.
This suggests to me that the vacuum solenoid is defective, has a bad connection/broken wire at the solenoid, or a bad connection at the microprocessor or a defective microprocessor. The wiring diagram shows one wire to the solenoid from the microprocessor, and a ground.
All very hard to see, as the connections are on the inside of the solenoid, and it's a jungle in there!
I have another microprocessor on hand, but I'd like to work from the solenoid back if I can.
Thanks for all the help!
GrandpaDan
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