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A/C and cooling fan 1984

Heyblue

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Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
So a little background. A/C was not working, the compressor clutch was not engaging. Using the Service Manual, including the addendum electrical one, concluded there was probable not enough Freon. Bought a kit to convert from R-12 to R134. In the process realized there was virtually no R-12, hence not enough pressure to closed the cycling and high pressure switches. Added R-134 using with gauge that came with one of the cans. Cooling started working.
So what is the problem? When the car is started cold with average ambient temperature the radiator fan comes on with out the A/C unit turned on. After warm up they seem to start cycling as you would expect, at least while siting in the driveway. There is only one indication that there is a pressure switch that causes the fan to come on when the A/C unit is on. I found it with no help with the manuals. It is on the compressor, it is a single wire. It does not seem like it is replaceable. I disconnect and the fans quit coming on with cold engine.
Question 1. Can it be replaced?
Question 2. What should the static pressure be in the A/C lines?
Thanks in advance
 

Heyblue

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Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
still looking for what the static pressure should be in A/C unit. I am thinking I may have overcharged the unit so the pressure switch that controls turning on the fan may be set without the unit running.
 

dougelam

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Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Yes, with an EMPTY system. I believe is held in by a snap ring

Refrigerant is a liquid, I don't believe that you can over pressurize it. But you can over fill it which causes poor cooling.
BUT I myself never used a suicide can to charge a system.

To answer your question refrigerant by nature has the same pressure as it's temperature. R134 is not exact like R12 though, so static pressure can't be high enough to cause problems.



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Hot Rod Roy

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Joined
Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
Refrigerant is a liquid, I don't believe that you can over pressurize it.

This is true, until you run the compressor! An overcharged system can easily exceed 400 psi! You are charging thru the low pressure port, and liquid refrigerant into the compressor can cause havoc!

With the compressor running, the low side pressure will be reduced, and therefore the higher pressure in the supply container will cause the refrigerant to flow into the system until the container is empty, or the system is overcharged! That's why knowledge and gauges are so very important. Without those, you're asking for TROUBLE!

:duh
 

Heyblue

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Joined
Aug 8, 2015
Messages
50
Location
Felton, CA
Corvette
1984
how much was the 134 kit and where did you get it?

Almost any auto parts store, They are cheap, less than $10. The "parts" are just diferent connectors to connect the gauges and R134 filler hose. They suggest changing the dryer, which cost < $30.00. real cost is evacuating the old R-12 then pulling a vacuum which requires a special pump or go to any A/C repair shop) before refilling with R134.
 

DonB

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Mar 25, 2015
Messages
339
Location
Chicago
Corvette
2019 ZO6 in Elkhart Lake Blue
This spring I converted my '90's A/C to 134a with the guidance of a licensed HVAC tech. First, you should evacuate any remaining(if any) R-12. Then,.. You should flush the system thoroughly. You can also use DE-NATURED ALCOHOL, because it is non-flammable or buy a flush kit(same difference.) Before changing the dryer or adding 134a. You should also add the correct type and amount of refrigerant oil for 134. It is called PAG oil. Be sure to drain the excess old oil from the compressor too. The total system holds about 7.5 ounces. When in doubt, check the FSM.

Failure to flush the system and remove all the old R-12 and it's oil will be a costly oversight! The different types of Freon when mixed WILL make an acidy mixture.

Sure it will work for a while, but you are contaminating the entire system.

We all know what ACID does! I don't think you want to do that.
 

dougelam

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Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
This spring I converted my '90's A/C to 134a with the guidance of a licensed HVAC tech. First, you should evacuate any remaining(if any) R-12. Then,.. You should flush the system thoroughly. You can also use DE-NATURED ALCOHOL, because it is non-flammable or buy a flush kit(same difference.) Before changing the dryer or adding 134a. You should also add the correct type and amount of refrigerant oil for 134. It is called PAG oil. Be sure to drain the excess old oil from the compressor too. The total system holds about 7.5 ounces. When in doubt, check the FSM.

Failure to flush the system and remove all the old R-12 and it's oil will be a costly oversight! The different types of Freon when mixed WILL make an acidy mixture.

Sure it will work for a while, but you are contaminating the entire system.

We all know what ACID does! I don't think you want to do that.
WOW I wonder what changed!
Back in the 90's and well into the early 20000s I retrofit literally hundreds of R-12 systems with R134A.
At first it was flush everything, replace all the O-rings, replace the dryer, drain the compressor Yada Yada yada

It wasn't long that it was discovered that by replacing the dryer, the service ports and adding PAG oil (I don't recall the amounts though) one would get the same results. There was a percentage of the R12 charge for determining the amount of R134A (don't recall that either)

It was said that what old oil was left in the system would settle out and end up at the bottoms of the condenser and evaporater and stay there without any issues.

I only had a couple of them come back for small leaks

I don't remember ANY of them not working our having acid issues since any R12 left in the system would boil off during the dryer replacement AND THEN what was left definitely would boil off during system evacuation, I liked a half an hour if not more.

Of course that was many moons ago

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DonB

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Chicago
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2019 ZO6 in Elkhart Lake Blue
Those were instructions from the HVAC tech. that helped me and Denso.
Of course I'm sure there are other options, I chose to heed his instructions since I was installing a new compressor from Denso, new hoses and condenser.
By the way, Denso Tech Support recommended the SAME procedure in order for them to honor the component warranties and avoid acidic contamination.
 

dougelam

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Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Those were instructions from the HVAC tech. that helped me and Denso.
Of course I'm sure there are other options, I chose to heed his instructions since I was installing a new compressor from Denso, new hoses and condenser.
By the way, Denso Tech Support recommended the SAME procedure in order for them to honor the component warranties and avoid acidic contamination.
You were very correct in your decision 👍
Always listen to the one controlling the warranty 😀

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DonB

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Mar 25, 2015
Messages
339
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Chicago
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2019 ZO6 in Elkhart Lake Blue
Thats kind of how I looked at it Doug. Especially since my HVAC guy is a friend and he works for beer!
 

DaveP85C4

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Oct 11, 2007
Messages
43
Location
Kalifornia
Ester Oil is the correct oil for use with R134 in a system that previously contained Mineral Oil.

PAG oil should NOT be used in R12 to R134 retrofits. PAG reacts with residual mineral oil and makes a mess that can only be cleaned up by replacing everything. PAG is fine for use in a system that has always been R134.
 

dougelam

Well-known member
Joined
Jul 19, 2011
Messages
453
Location
Michigan
Corvette
2002 Roadster
Ester Oil is the correct oil for use with R134 in a system that previously contained Mineral Oil.

PAG oil should NOT be used in R12 to R134 retrofits. PAG reacts with residual mineral oil and makes a mess that can only be cleaned up by replacing everything. PAG is fine for use in a system that has always been R134.
Your probably right, I had PAG oil on my mind from the dealership days

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