AC charging

[steve from staten island]

I have a new Classic AC unit in my 69 and recently tried to charge the system myself. The system held a vacuum at least a day or more. I then ran the vacuum pump for a hour and then charged it using the small cans. I got about 25 pounds in low side with engine running but the temp blowing out vent was about 58 degrees. There was no air going across the coil and the garage was well over 90. The high pressure side was only about a 100 and i thought it should be 150. Do i have to add to high side and can i still use little cans or do i need the big cans====Thanks

 

[wagonman]

Did Classic give a spec on how much to put in? Pressure sounds low on both sides. At 90 degrees high press should be around 200 and low 35-50. Compressor coming on?

 

[metaldad]

r12?
how many cans?
no air across the coil, yet air out of the vent was 58?
head pressure only 100?
wagonman is correct on pressures, r12 and 134 are close
i usually charge @ 1500-1800 rpm, with windows closed, back pressure above freezing, compressor not cycling

 

[metaldad]

you should also be cognitive of how much the system should hold, and how much you are dumping in.
plus, a non moving vehicle will run higher than normal pressures, because of lower air flow across the condenser
your pressures are suspect, as is the no air flow.
i have no idea how much gaaas is in those little throwaways.
i deal with much larger cylinders (1000#)

 

[Ranger16]

Do i have to add to high side and can i still use little cans or do i need the big cans====Thanks

NEVER EVER open that high side valve when charging the system. The ONLY time it gets open is when pulling a vacuum. Opening that high side valve subjects the can to the high side pressures. I don't know what pressure those cans can withstand, but high side pressures can exceed 200 psi. That's like playing with a hand grenade.

 

[wagonman]

Doubt it is R-12 but ya never know. I picked up a cool old Dupont cyl at a yard sale about 1/3 full of the liquid gold for $25.

 

[oldbee]

I think a "can" is considered a lb. Your press is low, maybe system not filled enuf?

 

[steve from staten island]

I understand about the high side being filled with system off, engine not running. But do you need to put can upside down and fill or is all done from low side with freon in gas state. Using 134

 

[Ranger16]

It's all done from the low side. I have turned the can upside down and serviced as liquid (I know that is technically wrong, but it worked for me many many times).
R134A is irrelevant. The principal is the same whether it's R12 or R134A.

 

[steve from staten island]

What does the high side pressure tell you and thanks for the help

 

[451Mopar]

I weighed my cans before and after filling to know how much was put into the system.
When filling, I had to run the engine at a higher RPM and shake the can for the low side to empty the can.
My Vintage Air setup only takes 1.8 pounds (a bit less than 2 cans.)

 

[oldbee]

I concur with Ranger16; from the few I've done with cans(running-low side) the system won't take anymore when it's full. I've usually done it with charging stations where you put in the correct amount needed. The high press turns the gas back into a liquid that's needed for heat transfer.

 

[Ranger16]

You CAN overfill an A/C system. "Full" is a relative term. You never want to "fill" it till it won't take anymore.
The "proper" way is to recover the refrigerant, pull a vacuum and recharge with a known weight.
Using pressure gauges as most of us do is a close approximation.

 

[Ranger16]

What does the high side pressure tell you and thanks for the help

Don't mean to sound like a wise ***, but it tells you what the high side pressure is. Not sure how else to explain it.

Maybe this will help.
http://www.acpartshouse.com/how-an-air-conditioner-works
Table of refrigerant pressures vs. ambient (outside) temperature
Ambient temp Low side pressure High side pressure Center vent temp
60°F..........................28–38 psi................130–190 psi.............44–46°F
70°F..........................30–40 psi................190–220 psi.............44–48°F
80°F..........................30–40 psi................190–220 psi.............43–48°F
90°F..........................35–40 psi................190–225 psi.............44–50°F
100°F........................40–50 psi................200–250 psi.............52–60°F
110°F........................50–60 psi................250–300 psi.............68–74°F
120°F........................55–65 psi................320–350 psi.............70–75°F

 

[oldbee]

The low-side press that Ranger shows per the temp range is what you would see after it sat all nite & before starting.That press would also tell you if ur low on charge because it wouldn't match with the temp. range .

 

[toolmanmike]

I think a "can" is considered a lb. Your press is low, maybe system not filled enuf?

Cans are usually 12oz.

 

[metaldad]

hmmmm........... ranger's table, is operating, with the conditions shown, without taking rpm into consideration.
an idle system pressure will not tell you if your are low, unless the vapor pressure is below saturated temp. the liquid will boil off, equalizing pressures to ambient. only if there is insufficient liquid (total charge) in a system, the resulting vapor pressure within the system will be less than saturated pressures at whatever the ambient temp is.
i would gather, you could affix remote mount gages to a vehicle, then take her for a spin. the higher the rpm, the more airflow, thus lowering head(hi side), with a correlating lowering of the back (suction) pressure
plus, an important fact, a vehicle sitting, with the a/c on, with the rpm 'revved' up, to the 1600/1800 rpm i already stated, the hi pressure side will be more than a moving car, due to the fact of the reduced air flow across the condenser a parked car will experience.
does this make sense? because i confuzed myself.

 

[Ranger16]

If I remember correctly, A/C should always be checked at about 1500 RPM, and I think a lot of shops will even put a large fan in front of the condenser, so I think you are correct.

 

[toolmanmike]

You rev the engine to provide proper airflow through the condenser. I replaced a dryer, vac'd the system down for a half hour, and charged the system using a set of gauges and a duct thermometer. With 90 degree ambient temps, I got mid to upper 30's center duct temps, 134 freon on a 96 Dakota with no electric cooling fan.

 

[metaldad]

well, you guys know cars. you guys know engines. some of you guys know what bolt went where. what the stamp behind the fluzzenhausser valve means and if its upside down, carl in the st. louis plant on the 2nd shift on the 3rd friday of june did that stamp.
if i know anything, i know air conditioning. yippee ki yay
small system, 30 minute vacuum might get you there.
it most likely will work. and probably work for a long time
but, did you use a micron gage to measure how deep of a vacuum?
vacuum test/ rise over time, to ascertain the thoroughness of the system repairs and the integrity of the system?
again, not a big deal.
just happy to chirp in, and not be completely off the beaten path.
lotta knowledge here. not attempting to rib anyone. thanks for having me.
excuse me, while i retreat to my corner