AC pressure/ cluch cycling info needed
01-02-2019, 11:16 AM
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AC pressure/ cluch cycling info needed I have a 2000 Firebird LS1/T56 in my 1989 Firebird. Everything is done except I'm having an issue with the AC. Its working, its pulling the temps down from 50-55 degrees outside temp to 29 degrees vent temp. However the AC clutch isn't cycling on/off. I have it wired so that the 89's ac selector feeds into the PCM, and I have the original 2000 pressure switch on the high side line (the combo one that senses low/high). The rest of the AC wiring is factory 2000 firebird (I'm running the under hood fuse/relay boxes). So if I turn off the AC the clutch disengages, and if turn it on it engages, so that seems to be correct, the issue I'm having is the clutch stays engaged when the AC is on, it doesn't cycle on and off like every other car I've worked on.
With gauges I'm seeing 30-35psi low and 200-250 psi high depending on time of running it and RPM on the engine. I still have the 1989 low side press sensor installed but it isn't wired in. With a multi meter hooked to the 89 low sensor/switch it never opens (it stays closed). The pressure equalizes once I turn off the AC.
All AC parts are new, new hard lines, had new soft lines made, new evaporator/condenser (89 part numbers), and a reman compressor (2000 compressor). I've put in 24 oz of R134 initially and have put in another 6 oz testing. I put the PAG oil weight/volume in as called out by the compressor paperwork. I would suspect the sensor/switch but since the 89 switch is also staying closed I suspect its something else. Maybe faulty compressor? Maybe the compressor has internal pressure valves and its working as it should for this compressor (Should a 2000 firebird compressor cycle on/off while its on when the outside temp is 60 degrees or so)? Maybe its just too cold to be testing the AC and it will just work right come summer.
Yes I pulled -30 psi and left it in vacuum state for 24 hours, verified it maintained it, then pulled vacuum for another hour before charging it.
What pressures should the PCM/sensor cause the compressor clutch to cycle on/off?
Should I be able to see the pressures using HP tuners on the 2000 PCM?
With gauges I'm seeing 30-35psi low and 200-250 psi high depending on time of running it and RPM on the engine. I still have the 1989 low side press sensor installed but it isn't wired in. With a multi meter hooked to the 89 low sensor/switch it never opens (it stays closed). The pressure equalizes once I turn off the AC.
All AC parts are new, new hard lines, had new soft lines made, new evaporator/condenser (89 part numbers), and a reman compressor (2000 compressor). I've put in 24 oz of R134 initially and have put in another 6 oz testing. I put the PAG oil weight/volume in as called out by the compressor paperwork. I would suspect the sensor/switch but since the 89 switch is also staying closed I suspect its something else. Maybe faulty compressor? Maybe the compressor has internal pressure valves and its working as it should for this compressor (Should a 2000 firebird compressor cycle on/off while its on when the outside temp is 60 degrees or so)? Maybe its just too cold to be testing the AC and it will just work right come summer.
Yes I pulled -30 psi and left it in vacuum state for 24 hours, verified it maintained it, then pulled vacuum for another hour before charging it.
What pressures should the PCM/sensor cause the compressor clutch to cycle on/off?
Should I be able to see the pressures using HP tuners on the 2000 PCM?
Last edited by Aviator857; 01-02-2019 at 01:56 PM.
01-02-2019, 03:11 PM
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oange ss thanks. I didn't realize the 4th gen compressor was variable (wish I had before I charged it I would of done the conversion to fixed). I had stumbled upon this just now https://ls1tech.com/forums/conversio...e-fixed-2.html
That would explain why the pressures self adjust for RPM etc but the clutch, when I idle it up the pressure rises some then falls back to nominal...
So it sounds like its all correct... any reason to wire up the factory 89 low side switch as a safety or will the 2000 sensor also provide the low freon protection (guessing it will since that is all the 2k car had).
That would explain why the pressures self adjust for RPM etc but the clutch, when I idle it up the pressure rises some then falls back to nominal...
So it sounds like its all correct... any reason to wire up the factory 89 low side switch as a safety or will the 2000 sensor also provide the low freon protection (guessing it will since that is all the 2k car had).
01-02-2019, 03:19 PM
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Follow up question should there be a temp sensor? (I have the air box from the 2k car so I can dig it out) Seems dangerous that its pulling the temp below freezing in the vent. Or was the original 2k set up only pressure based?