A/C Guru Question...?
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From: Ft. Lauderdale, Fl.
A/C Guru Question...? F-Body computer controlled LS1 w/Sanden 508 A/C system in a '96 GMC pick-up. Start up truck in driveway, turn on A/C, compressor kicks on & never kicks off. Ever. Take truck for a ride around town & compressor cycles off-on-off-on-off-on continuously, every 2 seconds. Both scenarios producing cold a/c. According to the gauge on the freon recharge can, the system is full & doesn't show any additional freon added on the gauge, even though I attempt to add more. Dual fans work perfectly. Have both accumalator cycling switch, and F-Body hi-pressure sensor plumbed into high side a/c line. Whats my problem? Oriface valve in the condenser line plugged, or? Very much appreciate any input you might have. 
Thanks
Thanks 
Staging Lane
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Off-on-off suggests high pressure in the condensor and the high pressure switch is cycling. But, it is a question when it runs all the time while you are setting still, unless the rpm is low and the compressor will not develop enough pressure to cycle the high switch. You might have too much freon in the system.
Do you know your hi and lo pressures?
I've found this forum to be very helpful for automotive AC systems. You may want to ask your question there: http://www.acsource.net/acforum/view...b2d137bad23587
I've found this forum to be very helpful for automotive AC systems. You may want to ask your question there: http://www.acsource.net/acforum/view...b2d137bad23587
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From: Ft. Lauderdale, Fl.
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Do you know your hi and lo pressures?
I've found this forum to be very helpful for automotive AC systems. You may want to ask your question there: http://www.acsource.net/acforum/view...b2d137bad23587
I've found this forum to be very helpful for automotive AC systems. You may want to ask your question there: http://www.acsource.net/acforum/view...b2d137bad23587
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From: Ft. Lauderdale, Fl.
Off-on-off suggests high pressure in the condensor and the high pressure switch is cycling. But, it is a question when it runs all the time while you are setting still, unless the rpm is low and the compressor will not develop enough pressure to cycle the high switch. You might have too much freon in the system.
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Verdad Gallardo The low pressure side of my Classic and Vintage Air re designed to operate at around 6 psi. The variable displacement compressors are designed to operate around 30 psi (low side). I'm guessing your ecu is working perfectly, it's just the compressor design that doesn't match.
I'm running Sandens off tha binary switch without the ecu on both my LS swaps, no problem.
Also, are you running any thermostat control on your setup (air temp)?
I'm running Sandens off tha binary switch without the ecu on both my LS swaps, no problem.
Also, are you running any thermostat control on your setup (air temp)?
Last edited by garys 68; Jul 29, 2011 at 07:15 PM.
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From: Ft. Lauderdale, Fl.
The low pressure side of my Classic and Vintage Air re designed to operate at around 6 psi. The variable displacement compressors are designed to operate around 30 psi (low side). I'm guessing your ecu is working perfectly, it's just the compressor design that doesn't match.
I'm running Sandens off tha binary switch without the ecu on both my LS swaps, no problem.
Also, are you running any thermostat control on your setup (air temp)?
I'm running Sandens off tha binary switch without the ecu on both my LS swaps, no problem.
Also, are you running any thermostat control on your setup (air temp)?
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Got A Set Of A/C Gauges... ...and hooked them up. Before I even started the truck up for the first time, I hooked up the gauges. Low side read 32 psi...High side read 33 psi. Started it up & turned on the air... Blows cold, at an idle...Low side now is +8 psi, high side is +58 psi. Compressor NEVER cycles off. Fast idle, low drops to "0" or even less. High goes to +68...compressor still never turning off. Disconnect everything & get in the truck & go for a city drive again. Compressor begins cycling on-off-on-off-on-off again. Accumalator & low pressure hose & fittings are cold & sweating. High pressure hose & fittings going forward to the condensor are so hot you can't touch them. Compressor also "extremely" hot. Any ideas, now that we have the PSI readings? Thanks again guys.
Last edited by LS1GMCTruck; Aug 3, 2011 at 01:23 PM.
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Another angle... I was doing some forum research, and read that a fellow was having transmission tailstock VSS sender problems, due to an oil leak, that was drowning his sensor with oil, from a engine or tranny oil leak. Does the 0411 F-body computer use any input from the VSS sender, with regards to A/C control? Weird sounding, but I had to ask, lol. Thanks
...and hooked them up. Before I even started the truck up for the first time, I hooked up the gauges. Low side read 32 psi...High side read 33 psi. Started it up & turned on the air... Blows cold, at an idle...Low side now is +8 psi, high side is +58 psi. Compressor NEVER cycles off. Fast idle, low drops to "0" or even less. High goes to +68...compressor still never turning off. Disconnect everything & get in the truck & go for a city drive again. Compressor begins cycling on-off-on-off-on-off again. Accumalator & low pressure hose & fittings are cold & sweating. High pressure hose & fittings going forward to the condensor are so hot you can't touch them. Compressor also "extremely" hot. Any ideas, now that we have the PSI readings? Thanks again guys.
At idle, suction (low side) is 8psi and discharge (high) is 58 psi? R134a saturated at 8 psi is about 4 degF; 58 psi saturated is about 60 degF. Even with the discharge at 68 psi that is only 68 degF. Are you reading pressure correctly at your gage manifold?
Actually most have tried the OEM variable displacement compressor with aftermarket AC systems. Results in that case seem to be decreased efficiency due to desing system pressures being different.
I just use the Vintage or Classic air system (sanden compressor) with trinary switches to control the compressor and fan. No problems and simple.
I just use the Vintage or Classic air system (sanden compressor) with trinary switches to control the compressor and fan. No problems and simple.
Vintage air recommends checking pressures with the engine at 1500 rpm. Normal range:
Low 6-12 psi
High 160-250 psi (general rule of thumb, two times the ambient temperature plus 15-20 %)
center vent output temperature should be 36-46 degrees
Low 6-12 psi
High 160-250 psi (general rule of thumb, two times the ambient temperature plus 15-20 %)
center vent output temperature should be 36-46 degrees
F-Body computer controlled LS1 w/Sanden 508 A/C system in a '96 GMC pick-up. Start up truck in driveway, turn on A/C, compressor kicks on & never kicks off. Ever. Take truck for a ride around town & compressor cycles off-on-off-on-off-on continuously, every 2 seconds. Both scenarios producing cold a/c. According to the gauge on the freon recharge can, the system is full & doesn't show any additional freon added on the gauge, even though I attempt to add more. Dual fans work perfectly. Have both accumalator cycling switch, and F-Body hi-pressure sensor plumbed into high side a/c line. Whats my problem? Oriface valve in the condenser line plugged, or? Very much appreciate any input you might have. Thanks
Thanks
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From: Downers Grove, IL
You are low on freon. Sounds like you are probably running 134a so make sure that your low pressure switch it set to cut out at 21psi. Next charge it till your low pressure side reaches at least 21psi running at whatever RPM your motor runs at normally on the highway. ( I prefer to charge till the low side reaches 28 psi that way I know I am running the evap core at ~32 degrees F and don`t have to worry about the system freezing up). Charging the low side to 28 psi does mean it will probably run at almost 40psi at idle which reduces the A/C`s efficiency at idle but it also reduces the risk of your compressor cycling on the highway which is hard on the clutch.
Teching In
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With the engine off, low and high side are at unity (equal) at 32 psi? That is LOW. If I assume the truck is at ambient (let it sit overnight), at 80 degF OD temp, r134a should be at the upper 80's.
At idle, suction (low side) is 8psi and discharge (high) is 58 psi? R134a saturated at 8 psi is about 4 degF; 58 psi saturated is about 60 degF. Even with the discharge at 68 psi that is only 68 degF. Are you reading pressure correctly at your gage manifold?
At idle, suction (low side) is 8psi and discharge (high) is 58 psi? R134a saturated at 8 psi is about 4 degF; 58 psi saturated is about 60 degF. Even with the discharge at 68 psi that is only 68 degF. Are you reading pressure correctly at your gage manifold?
The on off on off condition may be due to a low pressure sensor, though I'm not sure if these systems have them are not.
Last edited by QTB; Aug 10, 2011 at 04:36 PM. Reason: additional comment
