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Oh So Close
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Discussion Starter #1
The search helped me confirm that it is a vac leak causing my problem, however the search did not pull up much on the Hvac system other than to replace the check valve between the back of the intake and firewall. I am running an STS modified car w/Fast 92 - no check valve in that line. My boost gauge and BAP are connected into that line, but no check valve.

Situation: Car was running great, AC worked perfect. Went out for some racing - now AC only blows through the defrost setting (switch position on dash does not matter). Plus, the boost gauge is now reading 3 less/positive in the vac setting, hence vac leak. Where else can I check besides the two lines coming out of the firewall? I noticed the bottom line goes to what looks like a solenoid near the brake system on the passenger side wheel well.

I disconnected the vac line from the firewall and went straight to the vac input on the intake - gets suction, but no change on AC issue. My boost guage went dead, as expected, so that part of the system appears to be okay.

I ordered the helms manuals, but they won't be here for another week. I was hoping to find the problem by this saturday so I could hit the track.


Thank you for your time...
 

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Oh So Close
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Discussion Starter #2
Was just looking over the car again, I noticed a "noise" from the driverside interior cabin. Almost to the left corner of the guage cluster. Kind of a vac noise, or air pull. Anyone know if there are vac lines running in that part of the dash? Noise goes away when AC is on - or at least I can no longer hear it while the AC blows through the window defroster.
 

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Rambler is stuck in 2nd gear
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I had a similar problem. Except I have a check valve in the line. I don't know how yours works without one. I spent a lot of time looking for a leak and finally, I took off the check valve and looked really close at the end tubes where it plugs into hose and there was a little glob of sealant(silicone). I would think if yours was working and just quit, you may have this problem but in a hose somewhere since there is no valve.
Good luck--these little problems can be a pain to find.
 

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Oh So Close
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Discussion Starter #5
all your boost blew a hose off the AC control head or an actuator on the AC box. You need a check valve in the system somewhere.
Yeah, i figured that since it happened after a few races (and I blew a connector pipe on the turbo).. Where is the AC control head? Is that the piece near the brake system running to the lower line from the firewall?

Once I figure out what line blew off I will be putting in a check valve - already have it sitting in the garage.. :)

I had a similar problem. Except I have a check valve in the line. I don't know how yours works without one. I spent a lot of time looking for a leak and finally, I took off the check valve and looked really close at the end tubes where it plugs into hose and there was a little glob of sealant(silicone). I would think if yours was working and just quit, you may have this problem but in a hose somewhere since there is no valve.
Good luck--these little problems can be a pain to find.

According to the search on this forum that chk valve seems to be the main problem for everyone. I was hoping someone had a walkthrough on the hvac system, but no luck so far. Guess I will be waiting for my manuals to arrive.

It is a pain, but I will take this over electrical problems any day - played that game way too many times.
 

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Don't drink the Kool-Aid...
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Situation: Car was running great, AC worked perfect. Went out for some racing - now AC only blows through the defrost setting (switch position on dash does not matter). Plus, the boost gauge is now reading 3 less/positive in the vac setting, hence vac leak. Where else can I check besides the two lines coming out of the firewall? I noticed the bottom line goes to what looks like a solenoid near the brake system on the passenger side wheel well.

Thank you for your time...
Sounds like your HVAC system is operating in default mode (all air is channeled through the front defrost vents) which happens when there's a total loss of vacuum. You may have blown the supply like off the vacuum tank. The vacuum tank is attached to the left side of the HVAC box, right next to the steering column.

btw... there are no vacuum lines left of the gauge cluster.
 

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1LE
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13,384 Posts
You are going to have to climb under the dash while the car is running and look for the "hisssss". The vacuum hose has blown off the back of the AC controls in the dash, or a mode door actuator. I've never messed with our systems, but when the system uses vacuum to control the mode doors, there are a few diaphrams that have hoses going to them. Hopefully you can reach it without having to pull tons of stuff out.

Might want to go around and ziptie all your vacuum hoses as boost is new to them.
;)
 

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bananas
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7,356 Posts
By the title I thought you might have gotten my POS 05 GTO I traded in back in 07...haha

same issue, just i MADE it do it somehow when i cut something or didn't install something back
 

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Registered
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is it solved ?
 

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Oh So Close
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Discussion Starter #10
is it solved ?
Not yet. I looked at the lines going to the hvac system (as recommended above), but didn't see anything wrong. I need to pull them and double check. It has been raining the last three days, so I haven't been messing with the car much - just chilling with the family since I can't go driving. LOL....
 

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i had the same problem today and after checking i found one off hose going from the rear passenger side of the intake manifold to the fire wall and after i connect it the problem is fixed
i hope this will help you
 

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Has stiffer springs
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My car did this too after some futzing with the the OBDII connector caused some of the vacuum lines to get tugged on.

Just above the driver's right ankle is a black box with rounded edges. It's held in by a single screw. Remove that screw, take out the box and there's a vacuum line pushed into the back of the box. Mine had popped out.
 

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Don't drink the Kool-Aid...
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2,889 Posts
My car did this too after some futzing with the the OBDII connector caused some of the vacuum lines to get tugged on.

Just above the driver's right ankle is a black box with rounded edges. It's held in by a single screw. Remove that screw, take out the box and there's a vacuum line pushed into the back of the box. Mine had popped out.
That's the hvac vacuum box I mentioned above. There are two plugs; a black supply line from the engine compartment/firewall, and a white (visible in the photo) "out" to the air/con control switch. It shouldn't be necessary to remove the box in order to reattach the lines, just reach up and push-in the plugs to make sure they are fully seated. Also note the adhesive cover (in the photo) that keeps the lines/plugs secured under normal circumstances.

 

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1LE
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13,384 Posts
That's the hvac vacuum box I mentioned above. There are two plugs; a black supply line from the engine compartment/firewall, and a white (visible in the photo) "out" to the air/con control switch. It shouldn't be necessary to remove the box in order to reattach the lines, just reach up and push-in the plugs to make sure they are fully seated. Also note the adhesive cover (in the photo) that keeps the lines/plugs secured under normal circumstances.
That pic makes me want to cry.
 

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Never Ask Permission
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703 Posts
Mine did this once as well, it was a vacuum line by the back passenger side of the engine... plugged it back in, all was fixed...
 

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Oh So Close
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Discussion Starter #17
i had the same problem today and after checking i found one off hose going from the rear passenger side of the intake manifold to the fire wall and after i connect it the problem is fixed
i hope this will help you
Those lines were fine - i found the problem under the dash. Got some pics of it.

If someone would return phone calls...!!!! No worries, I needed to purchase the books anyways. I can't always borrow yours, and I am real good at breaking the difficult stuff.

That pic makes me want to cry.
It looks painful, but it helped me fix the problem.

Mine did this once as well, it was a vacuum line by the back passenger side of the engine... plugged it back in, all was fixed...
That one checked out okay as well.
 

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Oh So Close
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2,336 Posts
Discussion Starter #18
My car did this too after some futzing with the the OBDII connector caused some of the vacuum lines to get tugged on.

Just above the driver's right ankle is a black box with rounded edges. It's held in by a single screw. Remove that screw, take out the box and there's a vacuum line pushed into the back of the box. Mine had popped out.
That's the hvac vacuum box I mentioned above. There are two plugs; a black supply line from the engine compartment/firewall, and a white (visible in the photo) "out" to the air/con control switch. It shouldn't be necessary to remove the box in order to reattach the lines, just reach up and push-in the plugs to make sure they are fully seated. Also note the adhesive cover (in the photo) that keeps the lines/plugs secured under normal circumstances.
Thanks guys, it was that box that was causing the problems. The black line/hose had popped out. I pushed it back in and all is good. Now I just need to figure out where to install a check valve so that does not happen again.
 

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Oh So Close
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Discussion Starter #19
Fixed - Pictures

Took a few pics of the box where the line popped out; just in case anyone else runs into this problem.


Here is the box - take out one screw and the box drops down. Has two lines going to it; both covered with a padded adhesive material.


This connection had popped out - plugged back in and AC works great.



Reinstalled box...
 

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