A/C Charging Gauge Question...
 

Yes, it's that time of year when a young man's thoughts turn to driving his Porsche in cool comfort...

I am charging my '86 with Duracool (please, no flames - no pun intended really!) and am second guessing reading my gauges. I'm not sure if I'm reading my high side correctly. It has three scales and I think the one in the middle is for R12. What do you guys think of these readings (taken at 1800 RPM, engine lid closed, ambient temp around 81 deg.

http://forums.pelicanparts.com/uploa...1244910902.jpg
http://forums.pelicanparts.com/uploa...1244910954.jpg
http://forums.pelicanparts.com/uploa...1244910974.jpg

Pressure on the high side seems a bit too high, but I am not familiar with that refrigerant.
Do a search for a PE chart for that refrigerant.
Bet that discharge line is pretty warm too...

What I'm not sure of is which scale to read on the gauge in the last pic. Is it reading 140 or 210? Anyone got any idea?

As the high side gauge's markings indicate, the outside is for R12. ;)


Check the readings again at idle and let us know what you have ; also advise us of the outside air temp (ambient).

(approved and not approved refrigerants)
http://www.epa.gov/ozone/snap/refrigerants/lists/mvacs.html

let me know how the duracool went
Thnaks

Why are there apparently different guage scales/readings depending on the refrigerant? Why would 20 psi for R12 be different than 20 psi for something else or am I not reading the guage correctly? I was thinking you would just use the outside guage and fill till you got the correct pressures on the low and high side, after adjusting for ambient air temp...

Going by what readings you would want with r12 or r134a, your readings ae great.

Will do on the idle reading. FWIW, the outside temp with the readings I've shown was 81 degrees.

Thanks for the info on refrigerants. I really don't want this thread to turn into another debate over flammable refrigerants. It's already been debated ad nauseum.

Does it blow COLD air? That is the most important gauge reading.

The pressure indicated by the outside scale in PSI is always just that, pressure.
The scales on the inside, designated to refrigerant type indicate saturated refrigerant temperature that corresponds to that pressure.
Each refrigerant has different saturation temperatures, and that is why they are utilized in different applications.

I measured 64 degrees at the center vent while taking those pressure readings the other day. Cool, but not cold!

I was seeing about the same readings (reading outermost scale) on my gauges using duracool, and getting in the mid 40's at the vent while driving around in 80's ambient at night. I had pulled a vacuum for about 30 mins prior since my system had been open due to the rebuild. I'd put 3 cans (6 0z. each) which is what I came up with using the 35% ratio Duracool to R12 which is per instructions. Actually, it called for about 2.78 cans based on (Owners manual) 47.8 oz. X .35 = 16.73/6 oz cans = 2.78 cans.
Not sure if drawing off .2 cans would have that much effect. I still have the previous rec/drier in there so that's probably holding the temps up a bit as well. I did seal off the hoses while apart but I don't know how truly effetive that was. My plan is to add a Procooler but wanted to make sure everything was working reasonably well before I started "fixing" things.
Have you done anything to your system otherwise?

Bill, thanks for the gauge lesson! That's what I was trying to understand about the different scales. It's been a long time since my grandfather showed me how to use his gauges.

Buck, other than Duracool, my system is bone stock. I hope to add a Procooler at some point, along with more condenser area, and a more powerful fan. At this point, I'd settle for marginal. Virginia gets very hot and humid and I don't enjoy driving while sitting in a pool of sweat!

OK, took me awhile to get the time with the Porsche (Finally today. Happy Father's Day to me!). At idle, I'm getting readings of 40-42 PSI on the low side and right at 178 PSI on the high side with an ambient temp of 81. The vent temperature is 70.7 degrees. What do you guys think? Too much refrigerant or too little?

Your high side is safe and good, it could be a bit higher.
However your low side seems high for "normal", hence you are seeing higher vent temps.

Perhaps I need to bleed off some? I seem to remember an ideal low side of 25-38 PSI?

If we are saying the high side is safe and it could be higher, no, you would consider
adding more refrigerant if you were just looking at the high side. The low side reflects
what the evaporator core temperature is, and your high low side is telling you there is a problem.

Assuming the gauge is accurate, and that is first thing I would verify after seeing so many gauge or equipment issues over the years, I would say "maybe" you got air in the system.