A/C Vacuum Problems
Thread Starter
Heel & Toe
Joined: Feb 2005
Posts: 23
Likes: 0
From: Ny
A/C Vacuum Problems
Hello
Having trouble with vents, only blows on floor and defrost.
I think I have a vacuum problem on my 96 LT4. I have read about other people having the same problem. The Programmer seems to be working fine. Including the one under the steering wheel. The vacuum under the fuel rail is OK. Does anyone have the drawing of the vacuum layout. I want to trace it in from the engine compartment. Does it come out on the passenger side? I have the Driver Side apart but hard to see anything under there. Help. Thanks
Having trouble with vents, only blows on floor and defrost.
I think I have a vacuum problem on my 96 LT4. I have read about other people having the same problem. The Programmer seems to be working fine. Including the one under the steering wheel. The vacuum under the fuel rail is OK. Does anyone have the drawing of the vacuum layout. I want to trace it in from the engine compartment. Does it come out on the passenger side? I have the Driver Side apart but hard to see anything under there. Help. Thanks
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I don't have a vacuum diagram but there should be one in the engine compartment. There is only one Programmer. It switches doors based on the signals from the Dash Controls which are sent over a serial data line, so it's either not getting the signals or it's not responding to them. Programmer is linked to the CCM and the best way to verify that it's getting the signals is with a scanner. However, most of the time the Programmer causes these problems or the vacuum source has been lost so remove the Programmer and verify there's vacuum on the black line. If so, there should be vacuum at one or more of the solenoids and GM usually color codes these things to where Red or Tan is Defrost, Blue is the A/C Vents and Pink is the Heater. The solenoids are on the heater plenum, usually above and to the right of the accelerator. The important thing would be that as you switch positions on the panel, vacuum switches at the solenoids. If it doesn't and the vacuum source is good, then it's probably the Programmer.
Thread Starter
Heel & Toe
Joined: Feb 2005
Posts: 23
Likes: 0
From: Ny
Thanks, but it seems that the programmer is fine. I can't seem to get any vacuum at the programmer, at the black hose. When I suck on the hose from the engine compartment, It seems clogged. I can't get any air flow through it. I don't know if it is clogged or what? That is why I want to trace it from the engine compartment.
Safety Car
Joined: Apr 2003
Posts: 3,970
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From: Biloxi MS Theres something happenin' here, What it is ain't exactly clear.....
Same problem on my 96 as well.
two things I've read in the past:
Clean contacts on, or Replace the head unit.
or
Check the junction box/splitter under the driver's dash where all of the vac lines come together. Seems they get loose at this point often.
Thread Starter
Heel & Toe
Joined: Feb 2005
Posts: 23
Likes: 0
From: Ny
Ok There. Where does the vacuum line from the engine compartment enter into th einside of the inside of the car. Line is definitely clogged. I want to trace it and find where and what is clogging it. Thanks
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
The line may not be plugged up - there's a check valve so that vacuum can only flow one way - you're not suppose to be able to blow through it. Most of the LT motors put the valve under the fuel rail cover. It may be good from the valve to the Programmer, bad/broken/snapped from the valve to the source, so I'd look under the cover and find it to check it out. Otherwise, if you're sure it's plugged, disconnect it at the check valve, apply compressed air from the Programmer side.
Thread Starter
Heel & Toe
Joined: Feb 2005
Posts: 23
Likes: 0
From: Ny
My question then is? Does the black hose go directly from the programmer to the three pronged connector under the fuel rail?
One side works the Speed limit control and the other the A/c vacuum valves.
I've tried both blowing and sucking from both sides of the black hose, and I get nothing going through either end. Thanks for your help. I'll get it if it I have to tear the whole dash apart.
Hot in NY.
One side works the Speed limit control and the other the A/c vacuum valves.
I've tried both blowing and sucking from both sides of the black hose, and I get nothing going through either end. Thanks for your help. I'll get it if it I have to tear the whole dash apart.
Hot in NY.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
My question then is? Does the black hose go directly from the programmer to the three pronged connector under the fuel rail?
Yes, one side to/from the Programmer, the other to Cruise and then the vacuum tank and of course the third is from the source. If you can't blow or suck through one side of the valve, a new one will probably fix it. If you haven't done so all ready, verify that vacuum is flowing to the valve and for 9 bucks, I'd slap in a new one.
Yes, one side to/from the Programmer, the other to Cruise and then the vacuum tank and of course the third is from the source. If you can't blow or suck through one side of the valve, a new one will probably fix it. If you haven't done so all ready, verify that vacuum is flowing to the valve and for 9 bucks, I'd slap in a new one.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
PS: If you're trying to blow or suck through the hose with the valve disconnected but connected to the Programmer, you'd probably get the same result. The later years plug all the vacuum ports with the engine and/or the controls off. If you want to test the Programmer, albeit maybe just for a second, pump 10" of vacuum through the line on the firewall side of the valve and with the key in the run position see if it gets through to one of the plenum door solenoids. Red or Tan is usually Defrost, Blue A/C Vents and Pink Heater. Orange is all most always outside air but it's solenoid is over in the passenger side Kick Panel area. If you can hear one of the doors move, the Programmer is ok.
