volavet

Trying to get smart on this issue before I confront repair shop. Had AC problem where air was not cold in 1996 Vette. Brought it to the shop, they did a complete HVAC test with no leak found, just a top off of AC. Now AC cold, but no air coming out of front vents, just floor and defrost. Is this just a coincidence or do they have to disconnect something to do the HVAC test which they failed to reconnect properly which is now causing the top vents to not work? Appreciate any help as I don't want to be one of those "it was working before" customers, but I think they must have done something since it was operational prior to the repair. I called and spoke to some tool and they said all of the AC work is done under the hood, not in the car, but I think he is wrong as I believe the go under the driver side floor, etc. Appreciate any input..

Mortsciguy

I believe floor vent/defroster duct is the default for "No or Low" vacuum to the HVAC. If the 96 functions the same as the 95, I have an easy fix to consider.
If you remove the plastic cover on the starboard engine fuel rail, you will find a vacuum nipple coming off the intake. It's about 2/3 aft of the front. There is a pregnant looking plastic "T" that comes from that port. That T tends to fail from engine temps. Mine fell apart when I tried to remove it. Replacement can be located at Auto Value parts stores. Dorman makes a replacement for about $6. That fixed the problem for me. I believe that part is used on all LT1 engines. Not sure about others.

dayle97se

I have a 96 and HAD the same exact problems as the OP.

Volavet: check that skinny vacuum line as Mortsciguy mentioned. Does your cruise control work? If so, then your problem is 99% the dreaded HVAC controller connections. Easy fix, just a pain to get to.

You will need to remove the driver's seat and both driver's lower knee dash covers to get sufficient access to the HVAC controller, which is a black 8-inch square box located directly above the accelerator pedal. It's held on by one screw, and is attached to the firewall.

If your problem is the same as mine and all other 96 HVAC "no-face-vent" issues, then check out the connections on this box.

Read post #14
http://forums.corvetteforum.com/c4-t...l-problem.html

As an aside, I also have a leak coming from the refrigerant. I replaced the hi/low pressure switch but that didn't fix it. I have a slow leak somewhere, and need the system recharged at least once a year. Is this common??

captgarys

I have the same problem in my 96. Also intermitant cutout and only get hot air. Mechanic thinks it's electrical. Probably in the compressor

volavet

Cruise control does not work? So does that mean its not the dreaded HVAC issue?

Cliff Harris

Go to an AC shop and have them use a sniffer on your car. They can find VERY small leaks. They'll do this test for free, hoping you'll pay them to fix it. My evaporator has a tiny leak that takes about a year for the freon to leak out enough that the AC stops working. Sniffer found it.

Mortsciguy

Just because the cruise does not work, it is no assurance that a bad T is the only problem. But it is THE place to start. Of the 2 lines that come off that T, one goes to HVAC, the other to the cruise control unit. That's why you always start by checking that T... that and the fact it's the cheapest and easiest malfunction to fix, and the Most likely reason for a malfunction in HVAC damper malfunctions AND cruise malfunction. Just check the darn thing! It does not even require hand tools to replace!

volavet

I checked the darn thing, replaced it, still no dice...

zioncat

I also replaced the vacuum conection under fuel rail in my '96 hoping to cure problem of no air from dash vents. No luck. Had to go under dash. Very hard thing to do. Almost gave up several times. But kept coming back to this site for encouragement. I ran new vacuum lines to bypass the defective connections. Took me about 8 hrs of tedious work, but when I got it back together, IT WORKED! My wife thought something was wrong because I let out a victory yell or two.

dayle97se

As an update to my HVAC leak, here is the results of the dye test. My iphone camera wasn't able to pick up the dye as brightly as it actually is, but I did use a black light at night. This is a pic of the Hi-Low pressure switch, on the passenger of the engine bay. Note that this switch was replaced on my car 1 year ago. What could be causing this leak??

dayle97se

As an update to my HVAC leak, here is the results of the dye test. My iphone camera wasn't able to pick up the dye as brightly as it actually is, but I did use a black light at night. This is a pic of the Hi-Low pressure switch, on the passenger of the engine bay. Note that this switch was replaced on my car 1 year ago. What could be causing this leak??

volavet

i was wrong, the Cruise does work, I just did not get up to speed when testing it originally. I have it back at the shop (non corvette specialists) and they say it is the HVAC Heater/AC programmer but trying to find the part. Is this the same unit as the one above the has pedal? Their terminology was not the same as the programmer comments above, but I assume its the same. I plan to get it done by an expert, but since I thought they originally caused the problem, I brought it back here first.

dayle97se

It's the same part. Some call it the programmer, controller etc. If the shop is willing to replace it new, let them. It goes for $400.

volavet

They are not, they just confirmed what I thought for $160. So now I need to figure out how to self repair as identified by fellow members... Hopefully I can find a local member to come help some weekend for a few hundred bucks. Thanks for the input and advice.

sledge_78

Volavet,

I have a 96 Grand Sport that has the same infamous HVAC vent issue. I have learned it is a common problem but fixable without having to
purchase another programmer unit. The original part must be removed and the fix is applied to the "nipples" which the plug in vacuum connector attaches to. There are several "step by step" posts regarding the fix on this forum. do a search and you will find them. However, for understanding what causes the problem you are experiencing: On the controller unit the plastic "nipples" are very thin and flexible plastic. The vacuum apparently causes the tips of the nipples to collapse and shut off the vacuum source to the relays which activate the doors to divert the airflow. The fix is real simple once the unit is removed from the vehicle. There is the difficulty as described above. The cost is all in the labor to remove and install the programmer unit. I would, read up on the forum posts to become familiar with the effort needed to fix this. If you do it yourself, which is feasible for some, the cost is near nothing and the fix is permanent. However, you will need to be a contortionist to get under there to remove it, or be prepared to stay in that position for the rest of your life. All in all, once you know the work involved you may find a shop or individual to remove it for you and then reinstall it. so you could get an estimate, The front seat comes out relatively easily and from there it's just wiggling under the dash and removing the screw that fasten it to the firewall and unplugging the vacuum connector. Reinstallation is the reverse it is really not rocket science. That was done by the fellow who discovered the fix to the nipples.

Good luck and let us know how you make out.

Sledge_78,

sledge_78

Volavet,

I have a 96 Grand Sport that has the same infamous HVAC vent issue. I have learned it is a common problem but fixable without having to
purchase another programmer unit. The original part must be removed and the fix is applied to the "nipples" which the plug in vacuum connector attaches to. There are several "step by step" posts regarding the fix on this forum. do a search and you will find them However, for understanding what causes the problem you are experiencing On the controller unit the plastic "nipples" are very thin and flexible plastic. The vacuum apparently causes the tips of the nipples to collapse and shut off the vacuum source to the relays which activate the doors to divert the airflow. The fix is real simple once the unit is removed from the vehicle. There is the difficulty as described above. The cost is ll in the labor to remove and install the programmer unit. I would, red up on the forum posts to become familiar with the effort needed to fix this. If you do it yourself, which is feasible for some, the cost is near nothing and the fix is permanent. However, you will need to be a contortionist to get under there to remove it, or be prepared to stay in that position for the rest of your life. All in all once you know the work involved you may find a shop or individual to remove it for you and then reinstall it. so you could get an estimate, The front seat comes out relatively easily and from there it's just wiggling under the dash and removing the screw that fasten it to the firewall and unplugging the vacuum connector. Reinstallation is the reverse it is really not rocket science. That was done by the fellow who discovered the fix to the nipples.

Good luck and let us know how you make out.

Sledge_78,

dayle97se

Has anyone else experienced this?