AC Clutch Cycle
Joined: Sep 2004
Posts: 3,147
Likes: 12
From: Downers Grove, IL
If your low side pressure is dipping down to 15 psi you don`t have enough freon. 15 psi on the low side = ~15 degrees so the evaporator would freeze up which is why the pressure switch is turning the clutch off every 10 seconds. You want about 28-30 psi on the low side which would = 33-35 degree discharge temps. I`m not sure how the VA cycling switches work but on the GM ones you can adjust them so that they won`t cut out until 19-21 psi so that the compressor doesn`t need to cycle much (that will let it get down to ~24 degree freon temps at the orfice tube but because of the inefficiency of heat transfer between the freon to the evaporator metal the outside of the evaporator usually stays just above 32 degrees and doesn`t freeze up.)
If your low side pressure is dipping down to 15 psi you don`t have enough freon. 15 psi on the low side = ~15 degrees so the evaporator would freeze up which is why the pressure switch is turning the clutch off every 10 seconds. You want about 28-30 psi on the low side which would = 33-35 degree discharge temps. I`m not sure how the VA cycling switches work but on the GM ones you can adjust them so that they won`t cut out until 19-21 psi so that the compressor doesn`t need to cycle much (that will let it get down to ~24 degree freon temps at the orfice tube but because of the inefficiency of heat transfer between the freon to the evaporator metal the outside of the evaporator usually stays just above 32 degrees and doesn`t freeze up.)
I spoke with a VA engineer before I left for Power Tour. Based on our conversation, he felt the system was working correctly on the cooling side and that either my temp readings at the vent were not accurate or there was something wrong with the blend door causing the air to heat up after passing through the evaporator. So I left it as is and took it on Power Tour.
I ordered a digital temp probe to do some more accurate testing this weekend.
I ordered a digital temp probe to do some more accurate testing this weekend.
Joined: Sep 2004
Posts: 3,147
Likes: 12
From: Downers Grove, IL
I guess it might not be for the VA system, I haven`t ever worked on one of their systems. I can`t figure out how they made it work with that low of pressure though, in that part of the freon 134a pressure/temp curve it should be turning the evaporator core into a block of ice unless they found a way to eliminate the moisture in the air before it hits the core.
Oh well as long as you were able to get the A/C working well.
Oh well as long as you were able to get the A/C working well.
Their low side cut off is a temp probe inserted into the evaporator coils. When the system is in max cool and evap coil hits 34F, ECU shuts off compressor.
Checked out everything again with the new thermometer and the vent temps are where they should be. Going to focus some on potential air leaks and more insulation on the trans tunnel.
Checked out everything again with the new thermometer and the vent temps are where they should be. Going to focus some on potential air leaks and more insulation on the trans tunnel.
My 68 corvette convertible with VA has more leaks than Obamas White House last week. Used to be the tunnel and footwells make the hot asphalt feel good on my feet after an hour drive. The VA unit blows really cold and makes the car tolerable on even 100 degree days.
I was looking on corvetteforum and found a couple references to units shipped with incorrectly installed thermometers. Dont know if that's your issue but worth a check.
I was looking on corvetteforum and found a couple references to units shipped with incorrectly installed thermometers. Dont know if that's your issue but worth a check.
We replaced the thermometer on mine. Its definitely tolerable on a hot day. I just wouldn't call it ice box cold, which is what I was hoping for in such a small truck cab
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote
10 Reasons the LS7 Is GM's Most Extreme Naturally Aspirated V8 Engine Ever
Verdad Gallardo The first vent thermometer I was using was apparently not very good. The digital unit I picked up is showing vent temps around 46F. It warms up a few degrees once I get out on the highway, thats why I am looking into cab air leaks
TECH Regular
Joined: Jan 2010
Posts: 497
Likes: 4
ive been having similar problems with my VA system. It cycles on and off. im using the factory 6.0 compressor so i dont know if thats my issue. I am thinking of putting a test light on the compressor wire to see if the evap is shutting it off or the Trinary switch. I dont want a perm. jumper but i will if that means i have a colder car.
ive been having similar problems with my VA system. It cycles on and off. im using the factory 6.0 compressor so i dont know if thats my issue. I am thinking of putting a test light on the compressor wire to see if the evap is shutting it off or the Trinary switch. I dont want a perm. jumper but i will if that means i have a colder car.
