a/c vacuum
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From: Brandon MS
a/c vacuum
Does anyone know where the vacuum source from the engine compartment enters the cabin in the dash area. From looking at FSM it appears to be behind the radio. Just wanted to double check before pulling radio out. Thanks, John.
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From: Orlando FL
The source comes from the 3 connection check valve under the right side plastic cover of the engine. One hose is for the cruise and the other is for the vents. But it goes in that tubing and is hard to follow but that where it enters.
However I have had my radio out many times and I never remembered any hoses behind it that I could see, but was never looking for it. But the radio is in a basically plastic box and is probably pretty solid. I just don’t know what you will see doing that and looking there. You really need to get behind the whole assembly. The vacuum hose goes to the vacuum relays in the programmer which is above the gas pedal.
What actually are you trying to find out?
However I have had my radio out many times and I never remembered any hoses behind it that I could see, but was never looking for it. But the radio is in a basically plastic box and is probably pretty solid. I just don’t know what you will see doing that and looking there. You really need to get behind the whole assembly. The vacuum hose goes to the vacuum relays in the programmer which is above the gas pedal.
What actually are you trying to find out?
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From: Brandon MS
I'm chasing what appears to be a vacuum leak. I've checked everything and replaced all of the rubber hoses under hood as well as vacuum tank. When I put a/ c on dash vents there is a hissing at the defrost vent. Mainly in low rpms. When you accelerates it stops hissing but when you let off the throttle and coast hissing comes back. I want to check vacuum in the cabin where the line comes in. If that's good, then next step is the programmer which looks like a pia to get to. The fsm says to apply vacuum to each input on the programmer to make sure doors are operating. Just want to get rid of the hissing. A/C blows cold and there is some air coming out of the vents, but there is either a vacuum leak somewhere, or the actuator has a problem. Page 1B-13 in the fsm shows a diagram of the line routing and the source from engine compartment looks to enter behind the radio area.
Le Mans Master
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From: Orlando FL
Does it always hiss or just on one button function.
The hard hose converts so a soft hose inside the car. The programmer is hard to get to but not that bad in comparison to some other things. The main vacuum feed hose just does not pull off the niples of the programmer like other hoses. But if you drop the programmer down and look and listen, you may fine something. There is a hold down for the hoses on the programmer which is a PIA.
The hard hose converts so a soft hose inside the car. The programmer is hard to get to but not that bad in comparison to some other things. The main vacuum feed hose just does not pull off the niples of the programmer like other hoses. But if you drop the programmer down and look and listen, you may fine something. There is a hold down for the hoses on the programmer which is a PIA.
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From: Brandon MS
It hisses on auto, recirculate, bi-level, and vent. Does not hiss on heat or defrost. Also I did the diagnosis on the unit and it showed 00, no system faults.
Last edited by black-93-coupe; Mar 29, 2012 at 12:00 PM.
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From: Brandon MS
Found it! The source line comes into the dash on passenger side just above knee bolster. I checked vacuum from source and it holds steady, no leaks. Checked vacuum on black line that goes to programmer and it holds steady, no leaks. Now for the fun job of getting to the programmer and checking it.
The hissing seems to be happening because the defrost door is not fully closing when the air is directed out the dash vents. This appears to be controlled by the tan vacuum line. Guess that's where to start.
The hissing seems to be happening because the defrost door is not fully closing when the air is directed out the dash vents. This appears to be controlled by the tan vacuum line. Guess that's where to start.
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From: thayer missouri
on mine the vacume solonoid inside the programmer was bad to the defrost. because the spring on the defrost door is so strong it takes 15 inch's of vacume to close it all the way. u can replace the individual solonoids if u cant find a decently priced one. i have a few of them if u need one. sounds like there might just be something keeping the door from closing all the way. just a thought.
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From: Brandon MS
@woody, sounds like that's probably it. I drove around with vacuum guage on the line coming in from engine and it was 22"-24" of vacuum. Never below 20". When its hissing I can see that the defroster door is not shut all the way and the foam around the door is good.
I put the vacuum pump on the black line going to the programmer and it held steady at 20" with no leaks.
I'll have to wait till next Wednesday (next day off) to pull the programmer. Are the vacuum solenoids something you can buy at auto parts store? Once I get it apart I'm going to want to get it back together as fast as I can. It's starting to het hot in Mississippi, especially in a triple black car.
Do you have a part number for the solenoid?
I put the vacuum pump on the black line going to the programmer and it held steady at 20" with no leaks.
I'll have to wait till next Wednesday (next day off) to pull the programmer. Are the vacuum solenoids something you can buy at auto parts store? Once I get it apart I'm going to want to get it back together as fast as I can. It's starting to het hot in Mississippi, especially in a triple black car.
Do you have a part number for the solenoid?
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From: thayer missouri
i got mine from a guy in ohio. when i was trying to find a programmer some one gave me his number and he sent me two programmers. when u get the programmer out u will find a circut card and six solonoids. the blend door is spring loaded so it directs air to the vents and defrost incase it fails. the parts are nos and u cant order them from chevy. where are u at in mississippi, i work into memphis every two days or so i might be able to meet u and give u the part and explain how it needs to be soldered in on the card. there are only three joints so it is pretty simple. or i can just send u one when u figure out which one is bad. like i said make sure there isnt something blocking the door from closing completely. when i was trying to figure mine out i ran a hose from the plenium to the defrost actuator to isolate the the programmer and make sure it was the problem.
jim
4172701454
jim
4172701454
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From: Brandon MS
Jim, did you run the vacuum line directly to the tan line that comes out of programmer? From looking at fsm it appears that the tan line goes up to the actuator by the defrost vent area?
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From: thayer missouri
what i did was take the dash cover pad off and u can see the defrost acuator. hooked the line from the plenum there. if u have a hand vacume pump u can hook it to the acuator and ck it that way. i just wanted to make sur the plenium vacume would close it.
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From: thayer missouri
the one thing i didnt touch on yet is make sure u get power to the solenoid from the control head. the solonoid is just a electro magnet. with power applied it holds a ck ball in place and applies vacume to the tan line. when u look at the back of the programmer i will make sense. u will see the vacume lines and solonoids.
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From: thayer missouri
the programmers on my 87 is right above the gas pedal. there is a 3x5 box with a relay attached to it the relay is the rear defrost relay. u will see the six vacume lines comming from it. u have to lay on your back under the steering wheel.
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From: Brandon MS
Appears to be fixed. Took off the dash pad and checked vacuum going to defrost actuator valve. Vacuum ok. Noticed when I set a/c on vents that the actuator needed a little help to go up all the way. Helped it up and put some dielectric grease on the plunger. Alternated between defrost and vent a few times, put a little more grease on it. Cycled between defrost and vent again, and it goes all the way up (closed) on its own. Let it set a few hours, cranked the car up again and tested valve again. Seems to be working fine. Wanted to give it some time and retest a few times before putting dash panel back on. Thanks to Jim for giving me the idea to attack this from the top side. Much easier than going at it from below.
