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1986 Porsche 911 AC Issues

  • 1986
  • 911 Carrera
Mileage: 
77 000
Heating and Ventilation
Melbourne Beach, 
Florida

 I had a schrader valve leak and slowly lost R12 to the point the AC was barely cooling. I fixed the leakage problem and at this time was at the point I was not going to put R12 back in for several reasons: cost, environmental and ease of obtaining it today. I have read a lot about a R12 replacement using hydrocarbon refrigerant called Enviro-Safe which cost about $5/can. I won't debate the pros and cons about using this refrigerant, only that it works. I called Enviro-Safe and spoke to their technical personnel and I liked the fact that you only had to use 1/3rd of amount of Enviro-Safe compared to R12 (13 oz vice 39 oz). 

With R12 I was barely getting a 25 degree delta T (temperature) between ambient and the center dash temperature. With Enviro-Safe installed which is colder and more efficient that R12 I am getting 38 degree delta T 88 degree ambient (80% humidity) and 50 degree center dash temperature. 

My compressor pressures with Enviro-Safe are Low - 40 PSIG and High - 240 PSIG with R12 pressures were 35 PSIG and 225 PSIG. I don't have any history as to what the original AC performance was when the car was newer, but I am told I am lucky to have what I have. I spoke to my local Porsche Independant repair shop, and he told me that they normally shot for 25 degree delta T as sufficient for these older Porsches. 

My question, is is 30 to 38 degrees delta T fine with these cars or should I shot for approximately 30 degrees center dash temperature vice the 48 degrees I am getting now?

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