72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

[John H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Here are a few pictures I took at KC to help out a friend who bought my 72 LT1 w a/c in 1985. It looks like your are missing the same solenoid as my friend. I have more pictures on another camera that I have not looked at yet. If you can contact me, I can put you in touch with the two owners. I can post more pictures or send you what I have. Also inside of my friends Holley is black like yours.
[ATTACH=CONFIG]54225[/ATTACH][ATTACH=CONFIG]54226[/ATTACH]

That looks like a TCS solenoid.

[Michael W.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

That would require me paying specific attention to the configuration of a post-72 Corvette, at least with regard to the carb setup and solenoids. I don't see that happening anytime soon.

Also used on some '68-'71 depending on carburetor.

[Ed H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Roy here a few quick pictures taken in the garage. photo 3.jpgphoto 1-2.jpgphoto 2-2.jpg

[Ed H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Patrick and Michael from the helpful posts and my reading you are both are right. It is a set idle and anti-dieseling solenoid. Yes, it is unique to the 72 LT-1 year. This weekend I plan to double check the dwell, timing and then adjust to the higher idle rpm (900 rpm). This is higher than I prefer but seems no escaping that as stock configuration for the engine to handle the a/c as there no a/c activated idle step up.

[Ed H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Gene, my 72 LT1 original has been asleep in a garage for the last 20 years recently rescued and brought back to life. The Holley was recently rebuilt a few months back however much of the running of the engine has been cold startup as the rest of the car was being adjusted and getting road ready. I suspect that given many cold starts without the benefit of road warm up may be contributing to the excess carbon in the throat/horn of the carburetor. I will also double the check the dwell, the timing, and fuel air mixture this coming weekend to make sure those are all in spec as some of that may be contributing factors.

[Patrick H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Patrick and Michael from the helpful posts and my reading you are both are right. It is a set idle and anti-dieseling solenoid. Yes, it is unique to the 72 LT-1 year.

I said it was both, he just said it was an anti-diesel solenoid. There is a difference - which is why I pointed it out. To call it "just" an anti-dieseling solenoid is to miss its most important function on a 1972 Corvette.
The solenoids function the same for all 1972 Corvettes; just the bracketry holding it to the carburetor differs between a Holley carb and a Quadrajet carb. In fact, the solenoid portion of it is exactly the same.

And you are correct in that each year used solenoids attached to the carburetor in a different fashion.

Anyway, good luck on getting the tuning right. It's not that difficult once you understand how it's supposed to be done.

[Dave S.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Here are a few pictures I took at KC to help out a friend who bought my 72 LT1 w a/c in 1985. It looks like your are missing the same solenoid as my friend. I have more pictures on another camera that I have not looked at yet. If you can contact me, I can put you in touch with the two owners. I can post more pictures or send you what I have. Also inside of my friends Holley is black like yours.
[ATTACH=CONFIG]54225[/ATTACH][ATTACH=CONFIG]54226[/ATTACH]

Wayne,
your photo seems to show a pre 1972 TCS switch with a gas line bracket. The bracket and switch should be one piece (part number is not available to me but should be in the AIM). There is excellent information on CEC/TCS systems in the archives posted by Jack Humphrey. Researching that will answer all the questions.

[Wayne P.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Thanks Dave, I did find an article, that is Jack wrote for the Driveline dated 20 February 2005 and was posted in the Rocky Mountain Chapter newsletter in 2006. 71 was a one year only and the article states that the 72 had a TCS solenoid added. I will do more research. I wil forward the article on to my friends.

http://ncrsrmc.org/Downloads/Mar-2006-Newsletter.pdf

[Ed H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Thank you Wayne for the added info. From what I read I do not think the late model 72 Lt1 had the TCS solenoid on the right side for the the timing advance control mine does not have the wiring for it.

[Kevin G.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Congratulations Ed,

Here is a couple pictures to help.

I can't remember the RPM drop when turning the AC on, with my 72 but I can start it up perhaps later today and test it for a comparison?

[Wayne P.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Ed, For reference, the pictures I posted are from a July 18th build. +/- a day. I am using corvette. I think that is witinin the last week of production. I have some other info on the other cars wiring that build was on May 16th. I sent a PM with my phone if you want to give me a call. I am interested in learning more about your car and on this subject. It seems the three all may have different wiring. The other owners are willing to also share info also. I am using Corvette Birthday Calulator App as a reference. The owner would have to share the serial numbers.

[Ed H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Kevin, thank you for the pictures. Mine does not have the TCS solenoid on the right side. From what I have read the late model 72 LT1s did not have it (mine was built in June 72). What rpm drop are you seeing with the a/c turned on ?

[Patrick H.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Mine does not have the TCS solenoid on the right side. From what I have read the late model 72 LT1s did not have it (mine was built in June 72).

Ed,

What source did you use for this info?
I have seen cars made the last week of production that have the TCS solenoid on the right side.

Patrick

[Michael C.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

I want to weigh in on the discussion as I have the 1972 LT-1 AC car which Wayne was speaking about. Although I aced my ops check at the 2014 National convention in KC, I had to contend with the same problem as Ed, and had to get everything fully tuned and humming properly before my AC would run at idle without stalling the engine. Of course you have to make sure the AC compressor is working properly, too. Even with all that, and a 900 rpm curb idle, the AC will still drag the engine down 1-200 RPM. It runs fine at that speed, however. There is no "kickup" solenoid on a 1972 LT-1, but there is a TCS solenoid on the RH side and an anti-diesel solenoid on the carb on the LH side, as has been explained. Often the smog and TCS solenoid were removed on these cars by a past owner and the wires clipped off.

I hope this helps, but Ed, feel free to write me directly if you have any more questions and I'll try my best to answer them.

[Kevin G.]

Re: 72 LT-1 with A/C - rpm drops signifcantly with the a/c compressor on

Kevin, thank you for the pictures. Mine does not have the TCS solenoid on the right side. From what I have read the late model 72 LT1s did not have it (mine was built in June 72). What rpm drop are you seeing with the a/c turned on ?

Ed,

First let me say thanks for giving me a reason to take off the cover and start her up!
I'm not familiar with the "late w/o solenoid", I'd have to see your source?

Just as mentioned above there was about 100 to 150 drop in rpm when operating the AC. However, after returning from a quick run, maybe 10 miles the car would barely idle and stall when turning on the AC?

I really enjoy learning about these early emission control systems. I recall vividly the public's desire to control pollution in the early seventies.