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This is an old thread, but I was looking for something else and ran across this I felt like adding my experiences.
For anyone in the future, I fought my Vintage Air Gen IV unit quickly cycling going down the road but it worked perfectly at idle. After 2 years, 2 different Gen IV evaporators, multiple diagnosis with VA techs. We learned that the Denso 10S20F and 10S17F compressors (sized for larger late model orifice tube systems) are just too big of a pump for the smaller evaporator core in the VA system. I finally switched that to a Sanded SD5H14 (508), it worked well going down the road but was just passable at an idle in my K5 blazer here in the Phoenix summer. I switched to the Sanden SD7H15 or the (709) as VA refers to it as, and have found a happy medium. It still doesn't cool as well as my 10S17F did at an idle but it is much more stable at controlling the evaporator temperatures 1500-2000 rpm once the truck cools down. So, if you've experienced something like this, I would suggest looking at going to a smaller compressor from the Denso GM truck line.
You definitely stress tested yours more than I have. I rarely see >85F.
Thanks for the info!
Were I to move a few miles or more East, I'd need this I'm sure.
This is an old thread, but I was looking for something else and ran across this I felt like adding my experiences.
For anyone in the future, I fought my Vintage Air Gen IV unit quickly cycling going down the road but it worked perfectly at idle. After 2 years, 2 different Gen IV evaporators, multiple diagnosis with VA techs. We learned that the Denso 10S20F and 10S17F compressors (sized for larger late model orifice tube systems) are just too big of a pump for the smaller evaporator core in the VA system. I finally switched that to a Sanded SD5H14 (508), it worked well going down the road but was just passable at an idle in my K5 blazer here in the Phoenix summer. I switched to the Sanden SD7H15 or the (709) as VA refers to it as, and have found a happy medium. It still doesn't cool as well as my 10S17F did at an idle but it is much more stable at controlling the evaporator temperatures 1500-2000 rpm once the truck cools down. So, if you've experienced something like this, I would suggest looking at going to a smaller compressor from the Denso GM truck line.
Thank you Phillipm for posting this. I am new to the forum but have been reading while doing my swap and thought I would reply as I am sure there are others as frustrated by this as you and I.
I have a 5.3/4L60E swapped int a 1953 Ford F100 and have had this exact problem that I fought for a year. It would have great pressures at idle but as soon as I brought the RPM’s up it would cycle the compressor very quickly. Watching the gauges, it would pull the low side pressure down to 10psi in a matter of seconds which would tell the pcm to disengage the clutch. Rinse and repeat. I charged it in steps between 18 ounces to 36 ounces and the only thing that changed was the high side pressure. I stopped when the high side reached 300psi. Everything in the system was new except the compressor and I had the system open 2 times looking for a restriction. This was using the correct expansion valve and a “universal” drier.
I do not have a Vintage Air evaporator assembly but what I used is very similar. Your comments on the size of the compressor got me thinking about how these were used with an orifice tube by GM. Since what I had was not working, I thought I would try something different, so I removed the expansion valve and drier and replaced them with an orifice tube and accumulator. I put the orifice tube at the inlet of the evaporator where the expansion valve was and the accumulator in the suction line.
My ac system now consists of a 10S17F compressor, 260 cubic inch evaporator, 22” x 13” condenser, 3.5” diameter x 8” tall accumulator and black orifice tube that was used by GM in the donor truck. After vacuuming out and checking for leaks I charged with refrigerant and now have 48-52 degree air from the vents on a 92 degree afternoon. It still cools slightly better at idle. My pressures are 28psi low and 210psi high at idle and 20psi low and 230psi high at highway RPM. I think this may be slightly over charged now, but I was experimenting to find the lowest vent temperatures. This has eliminated the compressor “short cycling” at highway RPM’s.
Sorry for the long first post and I hope this information helps others overcome the same issue. While what Phillipm posted is probably the correct way to do this I just thought I could offer an alternative solution based on my experience. If the results change, I will update this thread.
Does anyone have experience with the Classic Auto Air setup? I know that VA seems to be popular, but based on what I have looked at, and I'm no HVAC engineer, it seems to me that CAA has a pretty decent setup.
Also, and I could be wrong, but it almost seems that a bigger evaporator might help mitigate the problem?
All these modern engines come with a variable displacement compressor, which neither VA or CAA can accommodate, but it almost seems like if you could get that accommodation, the problem could be solved?
Otherwise, I see that Holley is using that wide but shallow a/c compressor, and maybe that's the compressor you are referring to Phillip?
I posted this years ago because I originally believed VA saying that variable compressors cannot be used and that they would burn up. Both statements are false. I USED to have a VA system and I had a Sanden, the GM R4 compressor, and a GM factory variable compressor on it. Personally I believe that the GM compressors performed better than the Sandens. Since then I have ditched the VA for a factory hybrid ac unit with a variable compressor and would never go back. If you compare a VA system to a factory setup the evaporator alone is bigger than the VA box. Which one do you think will work better?
05-12-2020, 01:56 PM
