1991 AC Question
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1991 AC Question
Hello, I am a new member that is converting my 1991 F150 AC system from R12 to 135A. I have replaced the Compressor with a Denso. Also a new Motorcraft hose manifold, 1994 F150 Condenser (for 134A), VOV Orifice Tube, Drier and Green O-rings. The existing evaporator has been flushed too. The Denso compressor comes with 15 ounces of PAG 46. Is that ENOUGH Lubricant for the entire system? I have not evacuated and charged the system yet. I have done some research on adjusting the low pressure cut off Switch that’s on the Drier. I am still extremely confused on how to adjust it properly. I know where it is and about turning the adjustment screw. I have heard about the Theoretical temp part of the AC gauge (green numbers) need it be set near 0°C on the low side. Or the compressor needs to cut off at 22-24 psi on the low side. And the switch needs to cut off a little above the boiling pressure of R134 at 32F. But what I have not heard is exactly how you adjust the LPCO switch to do these things. I am confused. Tarkster
Lead Driver
Joined: Feb 2002
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From: Greater Austin, Texas
I believe 15 ounces is way too much oil. IIRC the correct oil amount for your complete system is 7 ounces. Someone correct me if I have this wrong.
If you will pull the electrical plug out of the LP switch, you will see a screw in the middle between the 2 spades. You turn that screw to adjust. I think counter-clockwise lowers the cutoff pressure. 22-24 is correct for R134a.
If you will pull the electrical plug out of the LP switch, you will see a screw in the middle between the 2 spades. You turn that screw to adjust. I think counter-clockwise lowers the cutoff pressure. 22-24 is correct for R134a.
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Joined: Feb 2006
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I think you are making this more difficult than it needs to be. I converted my 91 and my process was.
Add R134a adapters
Evacuate system
Replace Dryer
Add Ester oil to compressor (few oz I think)
Refill with R134a
Done
I would not use PAG oil, its not supposed to mix with the old R12 type, Ester can safely mix with both types.
I did this process over 18 months ago and my A/C is still ice cold and full. Its colder than my wife's 2011 Focus.
Add R134a adapters
Evacuate system
Replace Dryer
Add Ester oil to compressor (few oz I think)
Refill with R134a
Done
I would not use PAG oil, its not supposed to mix with the old R12 type, Ester can safely mix with both types.
I did this process over 18 months ago and my A/C is still ice cold and full. Its colder than my wife's 2011 Focus.
Logistics Pro
Joined: Mar 2005
Posts: 4,698
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From: Mexico, Missouri
PAG 46 is the correct oil for this conversion. It is what Ford calls for. It is light viscosity and there is PAG 100 medium viscosity and then PAG 150 high viscosity. I believe ESTER is only meant for R12, but I learn something new everyday. If the OP has completely swapped and converted the system, then PAG 46 would be the correct weight oil and 7 ounces would be ballpark. Ford changed oil amount spec after '94 from 11 to 7 ounces or so.
Also, adjusting the LP switch is correct as well.
Also, adjusting the LP switch is correct as well.
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Joined: Feb 2002
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From: Greater Austin, Texas
Mr Malina, if the OP were just doing a drain and refill, as you did, then no, you should not use PAG, you should use Ester. However, the OP is replacing all the components except the evap core, and the evap core was flushed, so PAG would be the correct oil to use.
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Posting Guru
Joined: Apr 2012
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From: Menifee, CA
7oz Pag46. The oil type is based around the construction of the compressor. Ford R12 compressors called for Ester oil, but since he replaced the compressor with an R134a designated model, Pag46 it is.
Also note the amount of refrigerant changed for the new compressor type. They originally said 33oz I believe, but a Ford TSB later upped the amount to 38oz of R134a
Also note the amount of refrigerant changed for the new compressor type. They originally said 33oz I believe, but a Ford TSB later upped the amount to 38oz of R134a
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From: mohave valley, arizona
agree with the pag, of system has new parts and been flushed completely. believe ester is for r12 and r134. but as i remember pag is better. im in arizona with 120 + temps, 200,000 miles on my old truck with the original r12 system, but its only a matter of time. dont know why someone doesnt make a complete conversion lit for these old truck yet, i bought one for my wifes 70 mustang, pretty cool, all the barrier hoses, high cooling condenser and compressor, well worth it, all a direct bolt in.
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Joined: Feb 2006
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agree with the pag, of system has new parts and been flushed completely. believe ester is for r12 and r134. but as i remember pag is better. im in arizona with 120 + temps, 200,000 miles on my old truck with the original r12 system, but its only a matter of time. dont know why someone doesnt make a complete conversion lit for these old truck yet, i bought one for my wifes 70 mustang, pretty cool, all the barrier hoses, high cooling condenser and compressor, well worth it, all a direct bolt in.
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