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Need advise on what to do with ac system--

playswithcars on Fri September 25, 2009 4:17 PM User is offline

Year: 1985
Make: Chev
Model: Monte Carlo SS
Country of Origin: United States

The car had been in storage for 15 years. I have replaced the original engine and trans with an LT1 and 4L60E from a 1996 Trans Am. It's all computer controlled.
I wanted to retain AC. The original system is R-12. However, I am using the LT1 compressor which was an R-134 system. My ac guy recommended R-134 and he custom made most of the hoses (barrier) and fittings. He evacuated the system for 45 mins and it held 25 in vacuum. He then recharged with the proper oil and R-134. It seems to work but it will reach high pressure very quickly and since the orig system only has a low pressure switch, compressor must be shut off quickly. I reprogrammed the computer so one cooling fan (has 2) comes on full speed at 170 deg coolant temp and stays running. If you wait until the fan comes on, turn on the system, it seem to work OK but I'm not happy with it. My question is, can I retrofit it and go back to R-12 using the R-134 compressor? What will be necessary to do just that. Totally confused and needing help.

Thanks,

Bob

mk378 on Fri September 25, 2009 4:27 PM User is offline

You'll still have the same problem. R-12 doesn't work either with no cooling of the condenser. The fans must run when the car is sitting still with the A/C on. There should be a switch or a sensor on the high side to detect when the pressure rises to about 250 psi and turn the fans on. This may be built into the computer already, you would need to plumb the sensor into the lines. Also there should be a provision to cut out the compressor at about 450 psi. That should never happen in normal operation but it is essential to prevent damage if the fans fail.

HVargas on Fri September 25, 2009 4:41 PM User is offlineView users profile

My recommendation is usually to keep the system R12. No difference here. To return it to R12 you will need to remove all the components and flush then, hoses included. Flush the compressor out with mineral oil. Drain the PAG or BVA oil and fill with mineral oil, turn the clutch a few times and drain it. Then add the proper amount of mineral oil back into the compressor. Flush the lines, condenser and evap. with a solvent based flush like our great like of Hecat Flush. Then replace the drier and vacuum the system and charge it with R12.

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playswithcars on Sat September 26, 2009 3:22 PM User is offline

Thanks for the suggestion.

Bob

jackhild on Sun September 27, 2009 10:11 AM User is offline

You could add a relay that activates via the compressor wire. The relay would turn on the electric cooling fan(s) when ever the compressor operates, regardless of coolant temp. This way you don't have to open the system or find a way to add a pressure transducer. This is pretty much what the Computer would do-the computer would activate the fan(s) based on pressures when the compressor runs.

You also need the highside cutout switch. You can buy on on the ACKITS commerce site. They screw onto your high side port, leaving an R134 access port available. You don't have to open your system to install. It wires in series with your compressor wire. https://www.ackits.com/pc/57807MD/conversionitems/57807MD+-+Low+-+High+pressure+Cut-off+Switch

Good Luck

Edited: Sun September 27, 2009 at 10:44 AM by jackhild

playswithcars on Mon September 28, 2009 3:09 PM User is offline

You also need the highside cutout switch. You can buy on on the ACKITS commerce site. They screw onto your high side port, leaving an R134 access port available. You don't have to open your system to install. It wires in series with your compressor wire. https://www.ackits.com/pc/57807MD/conversionitems/57807MD+-+Low+-+High+pressure+Cut-off+Switch



Good Luck



Sounds like a good idea to try. Thanks,

Bob

steve325is on Mon September 28, 2009 6:05 PM User is offline

I'm not sure how you have this wired up, but Pin 1 of the Firebird's black ECU connector is for a dk green/white wire from the A/C control head to tell the PCM that A/C has been requested. This will also turn on the fan. In fact, it will make sure that the fan is running before it engages the A/C clutch.

Are you using the Firebird fans running off of the Firebird ECU?

-- Steve

Dougflas on Mon September 28, 2009 6:17 PM User is offline

25 on the vacuum is not enough. If it holds at 25, I would think there is still moisture in the system. If the vacuum rises constantly, there is a leak. could be the system; could be the hoses/manifold.

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