1991 camaro rs 305 v8 th700r4 I am replacing the compressor, dryer, orifice tube and flushing the system, there is no r-12 in the system it all leaked out the compressor, i need to know how much r134a to charge the system back up with.

80% of what the underhood label says to charge it with. make sure you add the proper amount of oil after the flush

what does that come out to be in P.S.I? my car calls for 2.5 lb.s but i didnt have a scale handy to weigh some out of the 30 lb tank so i put in 40 P.S.I and its not blowing very cold

pressure varys depending on outside temps, the hotter it is, the higher the pressures, 30-60psi low side. high side should be aprox. 2.4 times the outside temperature 90* = 216 high side. this is for r134a, not r12

216 P.S.I?

its 95 degrees here today

ya so you are shooting for a high side pressure of around 230psi at 95* and aproximately 45-50psi low side

230 is a bit low on the high side in a high humidity, high heat area like Florida, and a R12 designed system. Expect more in the 250-275 psi range at idle. The low side will read around 50 psi at idle, high speed on the blower.

also true, humidity does play a role in the pressures, and so does the smaller design of and r12 condenser with r134a refrigerant. there are many factors that need to be considered when looking for correct pressures. i just figured that anyone who owns a set of manifold gauges already did some research on the subject, and knows what to consider when charging the system.

IMO i wouldnt spend a penny on my AC system, let alone use it especially if you have T-Tops its a sin to use AC, and if you dont have T-Tops just put your windows down, these cars already get bad MPG i dont even want to imagine what mine will get with AC on but thats just me, and if i were you i would rip out the whole AC system like it did, less weight, id say about 50+lb

lol! in your opinion you obviously dont live in florida. between the outside temp and the heat from the headers youd die in a day. not to mention my tops never come out since there is so much road work everywhere its like shovelling dirt straight onto your interior. in my opinion that measley 50lbs in weight is well worth it to me so i dont melt like a friggin snowman in a sauna or have an interior that smells like a sweaty locker room.

HAHAHA..... I bet your car gets better MPG with the T-Tops on and the Air ON than with the T-Tops off and the Air off...Killer change in aerodynamics with them removed and the windows down.

Fix your a/c and be happy... R134a SUCKS for your heat and humidity. I know first hand because we live in a very similar climate, super hot and humid.

When I am inching my way in bumper to bumper traffic at 5-10 mph for up to 30 minutes on my way home, I want ICE cold air sitting at idle and R134a cannot do it. Better than the windows down, but not nearly as good as R12.

i saw a study somewhere online where they did a test for better mpg with a/c on and windows up vs. a/c off and windows down. the conclusion was that on an average of 45 mph or higher you get better mpg anyway. obviously many factors are to be concidered for the appropriate speed, so it is just an average.

Yeah, I saw that on Mythbusters. It's too hott here in bama not to have a/c, so I know your pain.

Every car will be different. A Prius may get 60 mpg with the A/C off and 40 mpg with the A/C on. A 1 ton dually diesel might get 0.1 mpg difference. In the first instance (common among all low HP 4 cylinder cars too), turning on the compressor makes a huge drop in engine power.

I've measured the GTA with A/C on and off, and it seems to be 1 mpg.

I've measured average gas mileage in my Sunbird in summer and winter (no A/C in the car) and my wintertime gas mileage was about 2 mpg less. (30-40° ambient temps). Wintertime will always mean worse gas mileage as our cars take longer to warm up. Run richer when they're cold. Fuel doesn't burn as easily or completely when cold.

So ultimately on a year round basis. Running the A/C in the summer is aprox the same as driving around when it's a few degrees +/- around freezing outside.

Florida climate, you flat out need air conditioning. People would pass out without it. Small children need it. Even just going to the grocery store, your dairy products would melt/go stale earlier.

It's hard to measure refrigerant by system pressure alone. The temperaure makes a difference as does the condition of your system. A spotlessly clean condenser with radiator fan(s) on will have lower pressure than a plugged dirty system. The psi might be fine when you measure it (let's say 40 psi) but once you start driving, it might cycle off at 25 psi too often. Going by the pressure alone it looks high measuring with the hood open but low while driving (since the wind is dropping the pressure)

Even a simple bathroom scale is better than nothing for measuring your charge. Bring your equipment to an A/C shop. They'll probably have a digital scale or a tool that will measure in a specified weight amount.