Orignal R12 A/C Pressures Readings?

Here's an old R12 chart from the 60's.

John

Thanks. Can you give me a starting point? Do I assume if the outside air is 100 and I want 39.7 at the evap, then I should see 220 psi on the high and 43 psi on the low? Or do you draw a line across from the 100 degree / 220 psi to the 45.6 degree / 49 psi and end up with 220 / 49 when the outside air is 100 degrees?

quote:

draw a line across from the 100 degree / 220 psi to the 45.6 degree / 49 psi and end up with 220 / 49 when the outside air is 100 degrees?

Yes. The chart reads straight across. Actual readings will vary depending upon length of hoses, measuring point, etc.

John

suction 10 to 20 psi

discharge 180 to 225 psi

under these conditions

engine warmed up and running at 1500 rpm
temp control set at max cold
louver controls set at max cold air settings (Max AC)
Blower set at high speed

>add gas in 1/2 minute to 1 minute bursts (opening the tank valve about 1/2 turn)
>give the system pressures time to stabilize between bursts
>the pressures should slowly increase after each burst of gas
>eventually you'll reach a point where the system pressures no longer increase, they stabilize at the same pressure they had last stabilized at. This means you've reached the point where the receiver is beginning to fill with liquid freon. The system is full. Whatever the cold air temperature is, that's as good as its going to get.

Old systems never operate at textbook settings. When the discharge pressure gets to 300 psi, its time to stop and figure out whats wrong. The receiver has dessicant and screens inside which collect debris and cause the compressors discharge pressure to run high.

-G

Do NOT add in 30 sec to 1 minute bursts!! That is EXTREMELY dangerous. Without a scale you have no idea on just how much refrigerant you are putting into that pump, or its hoses.

If you are recharging an already partially charged system, go slow as you watch your pressures and temps. If your condenser is in the rear, have the deck lid open, if up front have the front trunk open. This keeps air going across the condenser since the car is not moving. Make sure the condenser fan is running.

Personally, I would change the dryer with one that has a sight glass, another tool to help balance a charge since you want liquid going to the Txvalve. George is correct about the receiver/dryer good and cheap practice to just replace them. Advise one with a pressure safety switch. It is very messy when a line gives way under pressure, and did I say dangerous? Clean up of all that oil is a bummer.

Read up on superheat charging to get the peak performance of these systems, do not go by outlet air, it is never accurate for charging purposes. The temp at the evap copper outlet is the most accurate.

Repeat, do NOT just dump refrigerant into a system for any count of time, that is just plane dangerous.

Hope that helps a bit,
Angelo

quote:

Originally posted by jb1490:
Here's an old R12 chart from the 60's.

John

John,
Where did you get that chart? I collect old a/c and refrigeration stuff, amonst other things. Ever see hoarders? Nothing on my garage, snicker.

Careful tho, most of those charts were made for specific pieces of equipment or cars. For instance, the operating pressures on a C-10 '70 pickup are not identical for a same year continental, or a 73 Pantera. They may be close but they are all different system with different operating conditions, also the same 3 vehicles in 3 different states with different humidity conditions....different operating pressures. The chart can be close as a baseline for R-12. I would still use a combination of guages, temperature sensor at evaporator and sight glass when charging, from a starting vacuum with my refrigerant tank on a scale. Once done, I would note the full charge for future reference.

Angelo

what i would do before adding any freon,is clamp off both heater hoses using pliers or clamps,at the engine.dont trust the heater valve for now.hot coolant flowing the heater core will change the guage reading and lead to a wrong diagnoses.put a thermometer in dash vent(i use a digital one)start car,a/c on max windows up doors closed.if you have guages hooked up good.next reach around to the compressor and feel the fittings/hoses,the larger one(suction side)should be getting colder and the other one (discharge side)warm to hot,too hot to touch shut it off and check condenser fan.did blocking off heater hoses change anything? it is ok to add freon in gas form, this means valve on supply up, turn it upside down,or shake it and you get liquid.add freon watching thermometer and guages.it should get colder each time you add a little and let it stablize. when/if the temp drops to around 50 degrees rotate the compressor control knob back alittle at a time and the compressor should start cycling off and on.then take clamps off heater hoses and see if that changes things.if cools good,compressor cycles, no abnormal noises,dont fix what aint broke

I really appreciate all the help and great advice, especailly the pressure ranges. As far as adding Freon, seems like the important part is to watch the gauges and add small amounts and not be in a hurry. Checking the sight glass and outlet air temp is good advice also. I think George's method assumes a close eye on the gauge. Some systems will balance out faster than others.
I have shut offs on my heater tubes, so that will make it easy to run some tests. Right now it blows cool, not cold air, and I really just want to find out if it is running as well as it can be given the stock compressor and condensor. At some point I intend to re-build the system with a rotary compressor and possibly a new evap and condensor. My hoses seem to be in great shape.

Is it the term "burst" that you guys are hung-up on? The term burst was never meant to imply dumping freon in at a high rate, or filling any "faster" than "normal". I've used the term burst to infer a differnce in proceedure from filling continuously until a certain pressure or temperature is reached. That's all. As I defined it ... a 1/2 to 1 minute interval and then close the low pressure manifold valve.

Between having the tank valve open only 1/2 turn and only opening the low pressure manifold valve the usual 1/4 turn or so, the gas is flowing into the system at a trickle, very slowly. The amount of gas admitted in that 1/2 to 1 minute interval will not register a decrease in tank weight on a digital scale. Its a slow process filling a system continuously, and filling it in bursts like this only slows the process more. Its a more cautious proceedure than a continuous fill, not the other way around.

The idea is to admit a little gas, then wait for the system to stabilize, admit a little more gas, then wait for the system to stabilize again. The pressures "should" slowly increase, the cold air temp should slowly decrease (I forgot to mention sticking a thermometer in the louver). By filling this way you're slowly nudging the system upward, inch by inch, and standing back and watching what happens. When the temperature stabilizes, the pressures should also stabilize; at that point the system is filled and the cold air will not get colder if more freon were added. If the discharge pressure climbs over 300 psi and things haven't stabilized yet, the system needs repair.

I've serviced the a/c in over a hundred cars belonging to other people (low estimate) over the last 40 years, more in bad condition than good. What I have explained is a more cautious way to fill a system of unknown capacity, in unknown condition, with an unknown amount of freon in it.

-G

Wasatch, I hope you removed the tiny screen-filter that resides in the evaporator valve under the dash before you started this exercise. The little conical screen is inside the side-leg of the evaporator, and in a 40-year old car, will be guaranteed plugged solid with rust, rubber flakes and pieces of broken-down dessicant. No freon flow= no cooling! If you're still using a stock York, the only value that antique has is its shut-off valves! You can isolate part of your R-12 by closing the valves, then untighten the side hose from the evaporator and hook the little screen out with a bent wire. Clean it carefully; solvents will dissolve the gooey rubber. With r-134a, some shops leave the screen out to increase freon flow & get more cooling. The whole system will work better with new-everything, incidently but especially a new dryer/dessicant can.

George,
My concern is not with the word burst, it is with the time frame mentioned. When charging any system, that amount of time can admit a large amount of refrigerant into any system.......depending on the tools used as you mention. Also, 30 seconds of liquid is a lot different than 30 seconds of vapor......BOTH by default will register on a scale, if it does not register, something is wrong and stop. Either you are not actually charging the system, or the scale is not working. period.

I have multiple refrigerant manifolds, from some old timers to the newer digital sets. All of the older units take multiple turns to open the manifold valves completely. Some sets open and close 100% with 'only' a quarter turn.

My main concern, and the reason I posted, is for safety. In another life I was the lone survivor of a 5 man crew in an industrial accident that due to a combination of poor practice and technician assumptions a liquid receiver ruptured killing 3 outright, 1 the next day. Luckily for me since I was the new kid was sent to a truck as a gofer and was about 20 feet away. Bad day for an 18 yr old. I have no clue on how many systems I have worked on since then, just too many. But admittedly, most in the commercial and industrial environments, I have stopped the automotive systems (except mine and friends cars) since I stopped being a line mechanic around '79 I believe.

Just this year, I was standing next to a car at a show when a refrigerant hose blew apart...refrigerant and oil cloud everywhere. This happened as the owner was proudly explaining to me how he had just finished charging the car......incorrectly.

I am just saying, be careful and SAFE. If you do not know the correct procedures to properly charge a system, either read up about it or have someone else that does know do it for you.

Have fun,

Angelo

Those details make sense and follow how an A/C system is designed to work. The "trickle" method should work well for me because it already has some amount of Freon in it now and I have no means at home to evacuate and weigh what is in there now. Have done something similar on my other cars, but had no idea what operating parameters the Pantera the requies to work right. This information helps a great deal. Thanks, Evan