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Old 11-12-2008, 01:14 PM   #1
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Default Converting your AC compressor from variable to fixed

I have been looking into using the stock A/C compressor in my LS1 conversion with a vintage air system. There seem to be a number of discussions about the variable displacment not working properly with the VA system. Comments like the compressor is too big from VA and the compressor will only run at 75% efficiency and it will live a short life are common. So far I have not found anything that confirms that they will not work properly if wired correctly. Information so far indicates that they may be better due to it adjusting automatically based on the load which seems to be the 75% efficiency and too big comments. These compressors are basically made to run and adjust displacement constantly which tells me that it they will not live seems to be another falsehood since this is what they are designed to do. I am not trying to dispute anybodys findings but to find the facts and to build a decent system. If anybody can tell me why these compressors will not work properly please respond. When searching for information I found this document that will convert the compressor to a fixed compressor but again I do not think this is needed.

http://209.85.173.132/search?q=cache...nk&cd=12&gl=us
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File Type: txt ACCompConv.txt (7.9 KB, 1706 views)
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Old 11-12-2008, 01:32 PM   #2
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I believe Bczee on here has a chevelle that has been running the LS1 variable displacement compressor with the stock chevelle AC system without any problems for over a year maybe more.
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Old 11-12-2008, 10:32 PM   #3
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Yup.. so far it has not had any ill effect to the system or parts and going on 2 years now
. Normally blow 47-50 degrees as long as I am moving...
I am sure that If I knew more about how a AC system works and did recharge it correctly, it most likely would work more efficiency. I say that only because it work good until I get into slow bumper to bumper traffic and then the system start to only blow cool air (55-60) but that's ok, most of the time in traffic I have the windows down and curising around anyway.. one of these days I will take the time to recharge it correctly or try other levels of coolant.

My setup is stock 71 Chevelle with only the 99 LS1 Z28 compressor wired up as the stock Chevelle compressor would be.
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Old 11-12-2008, 11:14 PM   #4
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Here's my understanding of it...

The Vintage Air expansion valve and evaporator are designed so that the low side pressure will run 6-12psi. The GM variable displacement compressor is is designed to run with a low side pressure of 28psi. At 12 psi, the GM compressor is A) going to run at full stroke constantly (no efficiency benefit, shorter life), and B) flow about 60% of it's normal full capacity (think about a turbo'd engine, and cranking back your boost from 28psi to 12psi--same principle).
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Old 11-20-2008, 03:12 PM   #5
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I have heard that about the pressures but again it does not make sense. A few of the A/C forums had some info where a variable displacement orifice tube actually will function more like an expansion valve. The second portion to that is it is really the low pressure side is what tells the compressor to kick in and the high pressure side is going to control the displacement. On the vintage air systems designed for R134 the system typically runs at 175/20 as high low pressures. I went to GM serpentine system before the swap with a GM compressor with no problems and it ran at the same pressures. I am not sure if there is some A/C parameters that can be controlled in the ecu to modify the on/off switch but maybe. The A/C forums state that the pressure is more like 22 to turn it on and it will run up to 34 before it turns off so that may be where you get the 28psi. An interesting note here is that the article I posted was to fix the high temp problem when idling...
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Old 11-26-2008, 11:53 PM   #6
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Default Bczee

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Originally Posted by bczee View Post
I am sure that If I knew more about how a AC system works and did recharge it correctly, it most likely would work more efficiency. I say that only because it work good until I get into slow bumper to bumper traffic and then the system start to only blow cool air (55-60) but that's ok
If you are running the oem chevelle condenser - that may be part of the problem - it was designed for R12 not 134 - its not as efficient as needed i would ad more airflow- electric fans - thats why OEM is using electric on new cars so much. a R134 condenser would help but how far do you want to go? add some fan(s) 2 behind pulling or even a pusher up front, its all about the airflow!
Now If your converting from R12 to R134 you generally use about 75% as much R134- yes less freon! also make sure you are using the proper lubricant in the system. so if your label says 2lbs of R12 use 1.5lbs of R134 - that should get you close. I have converted 3-4 R12 cars over and aside from a couple crappy new Delco compressors-a couple have sounded bad from the start but when working right they do it. In Texas A/C is not an option
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Old 11-27-2008, 01:35 AM   #7
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Ok folks,
In a past life I worked in a Chrysler dealership for 17 years 1983 - 2000.

When 134 can out there were HORROR stories of what could and what might happen. At one time I think there was 7 different pag oils for one year. We found that the BG 134 oil was the best and worked in everything.

The reason that there is a different Condenser and Evaps on OEM cars is that 134A is not as efficient as R12. So when you convert a R12 car to 134A it tends to run about 10 degrees warmer (in Nebraska) than when it was on R12. It took it aftermarket AC a couple of year to make the change on the Evaps & Condenser.

So could we just remove the aftermarket (Vintage Air) expansion valve and run the orifice tube?

But I think a Sanden compressor with clutch is cheaper than an OEM compressor and clutch.

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Old 11-27-2008, 02:10 PM   #8
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Heres my thoughts as I do Air conditioning repairs everyday.
Firstly a variable compressor can run an a/c system with a tx valve or orifice tube system either will work.
Secondly a variable compressor is an energy saving pump that provides capacity when demanded. Ie if the cabin is hot the low pressure rises and the pump goes into full stroke mode, if the cabin is cold and there is little heat load the compressor destrokes down to 5% of its capacity. The low side pressure is set at 28psi or there abouts so that the compressor never cycles and the clutch is always engaged.
Thirdly saying all this variable compressors have a low pressure setpoint that will correspond to the evaporator design and efficiency. late model cars are manufactured with thin walled evaporators that have a very small drop in temperature across the evaporator walls ie 28psi corresponds to 0 degrees celcius gas temperature which would corrrespond to a evaporator core temperature of 4-5 degrees celcius this is the best temperature for an evaporatore core to run so as not to freeze, but provide the best cooling. So if you were to connect your variable pump to an older thick walled copper evaporator your core temperature with the same compressor could be up to 12 degrees celcius and may not be icy cold at the vent but would still cool the car. I am sure that the vintage air evaporators are all aluminium and of average to slightly thiner wall thickness so you would need to match the compressor control valve to suit your application ie evaporator and may at would probably require a control valve that would give you a core temperature of 4 degrees celcius and this could be any where from 18-28 psi
I am planning on using a pontiac gto compressor with a gen4 vintage air unit in my 68 camaro so will let you all know how this performs when completed

hope this helps!
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Old 12-12-2008, 12:11 PM   #9
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I am doing the same. I have a vintage air that is a R134 system so the condesnsor and expansion valve should work fine with the new compressor. When I went to the serpentine I bought a adapter for my R4 compressor and the original hoses bolted right on. I have not put it on but it fits just like on the R4 unit.
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Old 12-23-2008, 10:26 PM   #10
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Default VD Compressor and Older Ac Systems

I'm running a OE GM (94 GTO) compressor on a Camaro LS1 that's been swapped into a Jaguar XJS. I was reading through this thread and it was very interesting. In my case, the LS1 engine in this car also runs the OE LS1 Camaro radiator, fans and AC compressor. However, the car itself (the remainder of the AC system) is OE 80's Jag with a thermostatic expansion valve and old design evaporator in the dash (originally set up for R12, and these pieces have all worked well with R134a on other Jag conversions I;ve done). The AC was put together more like a Camaro LT1 system with a high side receiver/drier in line back to expansion valve and no large accumulator on the suction side (the LS1 Camaros used that accumulator) and no orifice tube. I also have the Camaro high side pressure switch/sensor in the system.

Is anyone out there running the this style compressor with and expansion valve, and how is it working out??

My system was only recently completed, and on first charge up (with about 1 lb of R134a) the PCM will energize the compressor and it would run. However, low side pressures wouldn't drop bellow 30-40 PS, and high side wouldn't go up over 50. I was worried to add more refrigerant as I expected the suction side to go lower than that as the engine ran (and I didn't add more R134a). All the system did was slowly cycle the low pressure between 30-35 psi while the high side stayed pretty much at 50-60. MAybe this was ok, and I should have continued charging, but I thought I'd check first. The suction tubing was not cold, and the liquid line was not hot. No compressor noises either...

The expansion valve on the system is an older Jag part of unknown condition besides it not being clogged (the evaporator and x-valve were flushed out completely before recharging with R134a). Some sites I have seen suggest that an expansion valve that is stuck open could exhibit these systems...

Anyway, if anyone is running this VD compressor with an expansion valve (not an orifice tube) let me know.....
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Old 06-20-2011, 09:39 PM   #11
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Does anyone have a copy of the instructions on how to convert the V7 compressor from variable to fixed. The link in the first post above doesn't work. Thanks
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Old 06-20-2011, 10:31 PM   #12
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here you go..its a link to the PDF file..

http://www.aircondition.com/tech/get...9WYWx2ZXMucGRm
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Old 06-20-2011, 10:58 PM   #13
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From what I have read tonight is looks like the truck LS compressors are 10s20f or 10s17f compressors which are fixed displacement. LS1 camaros were V7 variable compressors though.
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"possible" is a relative term around here... anything is possible. It's "possible" to put a whole K3500 4x4 dually truck rolling chassis under a brand new Mini body. Is it reasonable? No. Does it make sense? No. Is it possible? Yes.
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Old 07-26-2011, 05:09 PM   #14
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G-Body, where did you read this?

I also found this: http://www.toyota-industries.com/pro...sor/fixed.html Even though it is a Toyota site, it lists the type of compressors G-Body was referencing.
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Old 07-26-2011, 06:01 PM   #15
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Quote:
Originally Posted by zman1969 View Post
If you are running the oem chevelle condenser - that may be part of the problem - it was designed for R12 not 134 - its not as efficient as needed i would ad more airflow- electric fans - thats why OEM is using electric on new cars so much. a R134 condenser would help but how far do you want to go? add some fan(s) 2 behind pulling or even a pusher up front, its all about the airflow!
Now If your converting from R12 to R134 you generally use about 75% as much R134- yes less freon! also make sure you are using the proper lubricant in the system. so if your label says 2lbs of R12 use 1.5lbs of R134 - that should get you close. I have converted 3-4 R12 cars over and aside from a couple crappy new Delco compressors-a couple have sounded bad from the start but when working right they do it. In Texas A/C is not an option
I agree with this. Put a bigger condensor in there, or some fans to maintain airflow when in traffic. Problem solved.
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Old 07-27-2011, 01:09 PM   #16
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Just came back from the AC hose place. They said my 10S17F is a fixed type. It's off an 06 Silverado. HTH.
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Old 07-27-2011, 04:33 PM   #17
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When I read the title of the thread, I thought the question was how to convert a variable stroke compressor to a fixed stroke. If that is of interest to anyone I've read of two methods, supposedly they both cause the variable stroke compressor to run at full stroke, ie., make it fixed stroke at max stroke.

1) Weld the tip of the plug in the variable compressor shut.
2) Take the 2 middle O-rings off that compressor plug.

Anyone have an experience with 2)?
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Old 08-15-2011, 10:51 PM   #18
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Quote:
Originally Posted by warpdriv View Post
G-Body, where did you read this?
I found it on the compressor works site http://www.compressorworks.com/defau...x?page=10PA10S
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Quote:
Originally Posted by Rodder
"possible" is a relative term around here... anything is possible. It's "possible" to put a whole K3500 4x4 dually truck rolling chassis under a brand new Mini body. Is it reasonable? No. Does it make sense? No. Is it possible? Yes.
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Old 08-19-2011, 10:12 PM   #19
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I've converted many R-12 systems to R-134 and regularly get 37deg fahr air from the registers with the vehicle sitting still and idling engine from 650-1500 rpms . With R-134 You're suction pressure (low side) at idle should be between 30-35 and go down to 15-20 when revved to 2000 rpm's in an older system .
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Old 08-20-2011, 09:35 AM   #20
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Don`t you have problems with the evaporator freezing up at 15-20 psi? That would be less than 20deg F. I thought you should lower the low pressure cutout switch to kick out below 22psi which is ~25 degrees, even at that pressure I usually see the evaporator starting to ice up.
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Quote:
Originally Posted by Rodder
"possible" is a relative term around here... anything is possible. It's "possible" to put a whole K3500 4x4 dually truck rolling chassis under a brand new Mini body. Is it reasonable? No. Does it make sense? No. Is it possible? Yes.
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Old 08-20-2011, 09:35 AM
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