1996 Corvette LT4

[Jim T.]

My 96 has the C4's optional air conditioning system. My LT4 is not a daily driver, mostly used for road trips about three times a year and stored in the garage up on a lift. About two years ago when using the air conditioning the cold air would come out of the floor outlets and windshield defroster. After about 15-20 minutes on the road it would switch to the proper dash vents. If I stopped on the trip en-route to my destination and get on the road again using the air conditioning it would blow out of the floor outlets and windshield defroster with cold air and after about the same time on the road would switch to the dash outlets to my destination.
I have the service manual and have read in the air conditioning section about using the electronic air conditioning panel to obtain codes for the systems it monitors. The -0000 is displayed like it should and then the 0000, continue pressing the button and 0000 is displayed showing no codes.
Has any C4 owners experienced the above conditions using the electronic controlled air conditioning system?

[Jake D.]

Re: 1996 Corvette LT4

The C68 AC is operated by vacuum. The junction on the firewall just above the accelerator is where all the vacuum hoses that regulate the AC system come together. There are little rubber barbs on the plastic connector where the two connectors join. The tips of the rubber barbs collapse and shut off the vacuum to the controller. You have to separate the two connectors and snip the ends of the rubber barbs to make them larger and less likely to collapse. This is a common problem with the C68 electronic AC. On our LT4 with the C68 electronic AC, I bought a '95 connector which has no rubber barbs to collapse. It worked fine for many years.

[Jake D.]

Re: 1996 Corvette LT4

Another possibility is the 3-way vacuum valve under the passenger side engine cover. If your cruise control isn't working, that's a sure sign that that 3-way vacuum valve is shot. These are easily replaced. Take off the engine cover on the passenger side and look around at the base of the intake manifold about half way back. Look for a small round plastic valve with 3 vacuum hoses on it. If that is broken it will cause your cruise control to stop and your A/C will go to default mode (only the lower duct and the defroster will work).

[Jim T.]

Re: 1996 Corvette LT4

Jake my cruise control works very good. I have always liked the function of just very lightly tapping the clutch pedal to disengauge cruise control. My air conditioning works fine after 15-20 minutes on my trips. I use my cruise control all the time on road trips.

[Rich C.]

Re: 1996 Corvette LT4

Sounds like our cars were born the same day! My A/C starts out blowing out defroster for about 10 seconds before working properly. But I just posted a thread about the control head, I have issues with that. Kind of wishing I didn't have C-68! But from what I've read, sounds like your programmer has issues. As another member said, sounds like the 'nipples collapsing'.


1973 LS-4 454 coupe owned 24 years
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[Paul M.]

Re: 1996 Corvette LT4

I wrote an article in the Florida Chapter Fueline this past issue on A/C and Heater Programmer. Email Ed Nieves he will send you the Fueline issue. To make a long story short. All '96 programmer will break down. It's not a question will it, it's a question of when. I failed my PV because of it. GM changed vendors to make the programmer. They made it with soft nipples instead of hard ones like all the previous years. You have to remove the programmer which is on the drivers side of the fire wall and send it to Taber Corvettes for overhaul the guru there is Sam. The cost is $375.00 + shipping. That's it. Your programmer will only get worse. If you intend to go for your PV you will fail. This Jan'15 at the Winter Regionals in Lakeland I will be going for my PV for the 2nd time. I have a CE'96 with 12,000 miles on it. So millage doesn't matter on this problem. Tom Barr C4 PV judge knows this problem very well. If you need more info send me a message and I will help.

[Paul M.]

Re: 1996 Corvette LT4

I also recommend you change your vacuum control check valve. On the LT4 it is on the passenger side of your motor. Take your valve cover off it's black with 3 vacuum hook ups.

[Rich C.]

Re: 1996 Corvette LT4

Any idea if this check valve is a GM service part? Last time I went to replace a vacuum fitting (Ford), they said it was part of an 'assembly' that cost $95.... for a valve, 2 plastic tubes and 2 pieces of rubber hose!


1973 LS-4 454 coupe owned 24 years (7 of those with a respectable front bumper)
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[Jim T.]

Re: 1996 Corvette LT4

Is your cruise control functioning OK?


Rick found this in a search. https://corvetteparts.com/item/valve...-lt4-1992-1996

[Rich C.]

Re: 1996 Corvette LT4

Pouring rain out today, so I can't check. But for $11....cheap insurance! Thanks for the tip. Also I have to try changing my VSS first. Malfunctioning is causing my odometer ticking off about 6 fold for every mile driven, speedo showing 220 mph!!! Not good! (unrelated issue). None to pleased for a car with 39,000 miles. Still love it though!


1973 LS-4 454 coupe owned 24 years
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[Paul M.]

Re: 1996 Corvette LT4

It's called a 2 way check valve part number #47150 made by Dorman sold thru Parts Geek. $5.00. It's exactly the same as the orginal. GM still makes the part for $5.00, but it's clear not black and it doesn't look the same( for judging ).

[Rich C.]

Re: 1996 Corvette LT4

It's called a 2 way check valve part number #47150 made by Dorman sold thru Parts Geek. $5.00. It's exactly the same as the orginal. GM still makes the part for $5.00, but it's clear not black and it doesn't look the same( for judging ).

Thanks!! I swear GM is in cahoots with re-pro companies. Can't they keep the same supplier for ANYTHING?


1973 LS-4 454 coupe owned 24 years
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[Jim T.]

Re: 1996 Corvette LT4

It's called a 2 way check valve part number #47150 made by Dorman sold thru Parts Geek. $5.00. It's exactly the same as the orginal. GM still makes the part for $5.00, but it's clear not black and it doesn't look the same( for judging ).

Paul, Thanks for your posted information on the check valve availability as a Dorman product. I checked a few of my local auto parts stores and found the Dorman #47150 at the Advance Auto Parts locally.

[Rich C.]

Re: 1996 Corvette LT4

Wow, that would be the first component I've ever put on my vettes from Advance Auto!


1973 LS-4 454 coupe owned 24 years
1996 LT-4 Collector Edition coupe owned 13 months
Sierra Nevada Torpedo IPA-currently on tap!

[David K.]

Re: 1996 Corvette LT4

Well go to Auto Zone and get it then. Dave