On my 1936 chevy coupe 5.3l LS swap I installed a Vintage Air Gen II complete kit (everything VA including lines, dryer, blower box, 2 wire high pressure cut out, etc, EXCEPT for Sanden compressor as I stayed with a new GM compressor).. As I live in north central Texas AC is a must. The Vintage Air system went in perfect and works great, absolutely no complaints. Now for the "possible" problem or better yet head scratcher. My VA kit called for a specific amount of 134a refrigerant to be installed on my complete new and dry kit install. No problem, as I have installed a few dozen of these VA kits into classics and they have always gone in flawlessly. I vacuumed the system down to the required specs, time and draw., found no leaks after 24 hours and proceeded to install the 134a (engine running, ac on and in coolest position). When installing the freon, compressor kicked on as it should and system drawing freon from supply just fine and all was looking good. I got within 3 oz's of the amount of freon called for in the VA specs and the system would not draw in any more freon, period. This stumped me as I have installed many hvac systems in both home and car and at any time I could over charge the systekm if I wanted. In fact several times I have over charged a system and had to release a few ounces. I install new freon systems by product weight, as is called for in most new systems and never had a problem.

So, how is it my system would not draw in the called for amount of freon? I even tried to switch to a new can of 134a, didn't work. I switched my freon manifold line kit and gauges thinking I may have a bad valve, no dice.

So my question remains, how is it I cannot get more freon into the system. Pressures vs outside tempretures vs humidity readings shows it should need a few more ounces to bring it to an optimal system. Have you ever charged a system that could not easily be over charged if you pushed it? The only deviation I took from the VA system is the AC compressor. I elected to stay with a new factory GM compressor as opposed to installing a new Sanden compressor. I have zero complaints how the system operates as both the heat and cool air are absolutely great. I'm just stumped that I could not get the required amount of AC into the system much less over filled.it if I chose to. Is this a possibility of compressor "dump" as my ac compressor sits lowest in the system? I need to be schooled.

 

Was there some residual PAG compressor oil in the system pooled up somewhere in the compressor taking up that space??

Rick

 

is it a variable displacement compressor or fixed displacement?

this is 100% theorizing, but the variable displacement compressor has vanes that self adjust to maintain the correct pressure on the low side. is it possible that when they make this adjustment, it reduces the system's ability to pull in more freon?

 

I'm not smart enough to provide details but when researching V.A. setups on a LS, everything I read is using the OEM compressor is far from ideal. Variable vs fixed displacement i think is what it was. When I do mine, I'm going to fit a Sanden compressor on

sounds like it will work, but be far from optimal and you won't get near the cooling capability the Sanden style compressor would give. I saw them for $150-250. Then figure out the bracket, or pay another $250 to ICT for theirs

 

I have a VA system in my 49 Chevy and I wrap a heating pad around the Freon tank. Sadly, the VA Gen IV system doesn’t live up to my expectations .

 

Possibly. That would actually accout for what I am experiencing. Great food for thought.

 

Rick,

I don't think so as I drained the pag that came with compressor and refilled it with correct amount. I typically don't drain and refill as pag I trust GM products. However, when I received this compressor some of the oil had drained out into box and I couldn't in good faith estimate the amountn leaked.

 

I have read it both ways, some like the GM comp others don't. I believe VA recommends the Sanden but I certainly don't always go by recommendations as I am a restorer/custom builder and quite often have to go outside the norm. i.e., LS into 36' chevy coupe. I actually have zero complaints on cooling capacity. This VA system in my 36' will run you out of the car within a few minutes as it cools down the cab fast. Thermo infrared shows 37 degrees at vent. However, will the compressor hold up in a VA system? Don't know, only time will tell. I'm still stumped I could not over fill the system and the last 3 ounces would not pull into the system. If the system does not hold up I'll change out to Sanden. It's these variances when building these cars that can keep you up at night scratching your head.

 

Update, have no idea why the last 3 ounces would not go into my system. There was a suggestion from bobcratch with an interesting theory which he may be on to something (see above). However, after using a thermo gun at vent which shows a low of 37 degrees out of register, driven this new build 400 miles as of today and have absolutely great cooling capacity, I'll run it like it is unless the compressor gives it up in a short period of time. If this occurs I'll switch to Sanden, but only if it fails in short order. About a week ago the temps here in Texas hit 93 degrees so I thought it was a good time to test this sysem with a drive. I literally cooled the cab down within 2-3 minutes. Drove new build for a 100 miles and system worked flawlessly. Within about 5-8 minutes I was having to cut back blower speed and temp **** as it was uncomforrtably cold in the cab. I was a bit surprised to see this cab cooled down so quick.

 

I'd rather have a little less than too much freon. VA told me this

 

Yep, absolutely agree as long as your pac oil level is correct your high press switch will continue to protect the comp.. I've been doing these auto systems as well as home HVAC since 1975 and I agree with VA. However, I am still stumped about not being able to bring up to specs or overfill. No, I do not want to overfill the system, but it would still be nice to know the mechanics of what is going on and why the system will not overfill. I think bobcratch hit on a good theory or possibly the line length. As I have the equipment to make my own AC lines I am able to custom fit lines to build. This reduces the amount of line I need to use and a form fit the build, which possibly reduces the amout of freon needed. Nothing learned nothing gained.

 

What deficiencies are you finding with the system?

 

Bob,

It's a variable displacement. These systems are designed to gradually bring up the line pressure as opposed to havig the comp engaged and being full on or off (which I think you possibly already know). I "think" GM's idea was to help save mpg. I'm starting to think this may be similar to an "on demand system or as needed" line pressure that works with the entire wiring system to coincide with the ECU, BCM to an inside thermostat. I'm only trying to understand this for future builds as the 36' chevy coupe is working perfect with the GM compressor. On this build I did an ECU AC delete to keep the VA a stand alone system, but I'm starting to think it may be better, if possible, to find a way to tie this system to an inside digital temp signal that the ECU can interpret if I want the max use from the GM compressor. Thank you for your imput, any further knowledge you want to share I would appreciate.