Is there a min ambient temp for A/C charging?

[mthomas58]

Was planning on doing the A/C charge this weekend. Just checked the forcast and we've got another cold front moving in with projected weekend highs in the mid 60's

The 134a PT charts start at 70 - 80 degrees. Rule of thumb says shoot for high side readings at 2.2 times the ambient temp.

OK to proceed, or should I just wait for hotter temps to charge?

[mthomas58]

el bump-o!

[GH85Carrera]

I am not an expert but here is what I learned. The biggest reason you want a warm day is to get a better vacuum on the system. We all know that water boils at 212 degrees at sea level. If you drop the pressure, water will boil off at normal ambient temperature. You will get more moisture out of the system because more water will boil on a 99 degree day than a 60 degree day at maximum vacuum. The one truism is you will never have to much vacuum before you charge your system. Even though the vacuum pressure will read the same, a 100 degree day will get more moisture out of the system than a 60 degree day.

How much moisture do you need to remove is like asking how much wealth is enough. There is no such thing as too much.

[brendon]

I just had to charge the system on my Jeep. I am no expert but this is what I found out...

Ambient temp at least 70 so your refrigerant bottle can provide enough gas. You don't want to add it as a liquid unless you are vac'ing out the system and adding by weight.

I assume you have the gauges and refrigerant. What I did, and this was at the advice of a 30-year refrigeration tech I work with, was hooked up only the low pressures side.
With engine off the low side gauge should be at about 70 psi. Start the engine and watch the gauge - when the compressor is running the gauge should read about 35 psi, if not add 134a as a gas while engine is running. Every time the compressor shuts off, the gauge will creep back up to around 70psi and drop back down to 35 when the compressor kicks back in.

This worked like a charm for me. Hopefully it doesn't all leak out before my vacation next month.

[Tigerrat]

I'm not sure about re-charge but when evacuating the system, the warmer the better to get max moisture out of the system. I'd wait. Ken

[3.2 CAB]

I never charge any A/C system without a complete gauge set. The high side pressures are critical and need to be observed. Decent gauge sets are inexpensive enough so you can have a dedicated set for R12/22 and a set for 134A. Maybe it is just me, but I like seeing the pressures on both the high and low side.

[mthomas58]

Originally Posted by Tigerrat

I'm not sure about re-charge but when evacuating the system, the warmer the better to get max moisture out of the system. I'd wait. Ken

Concensus here, PM's and other sources is wait for temps above 80 at least and the hotter the better to remove the moisture during evac.

I'll wait. It's killing me, but I'll wait

PS - yes I do have a shiney new vacuum pump and guage set just begging to be used!

Thanks for the replies!

[mthomas58]

Originally Posted by 3.2 CAB

IMaybe it is just me, but I like seeing the pressures on both the high and low side.

Didn't mean to imply that I was focused on high side pressures only with my comment - was just imputing high side pressures below the chart ranges using "rule of thumb" at 2.2 times ambient temps.

Don't know where low side and evap temps should be at charging ambients below 70 degrees. Perhaps that's why they're not published b/c evac charging conditions are not favorable for good DIY results.

Due to conversion to 134a and substantial system mods (2 condensers added) my actual refrigerant capacity is now "unknown" ,therefore, the charge must be optimized using the Pressure and Temperature charging method.

I've learned alot here guys! (I think)

[76911]

I haven't seen anyone talk about the most important part of charging a system.... that is how much PAG oil are you going to inject into this system?
Without any or very little you will burn up the compressor very quickly. That also helps with any moisture that might be left in the system Not knowing how muck R134a to put in is a problem without a good set of gauges or an A/C machine. At 75 degrees your gauges should read 28-34 low and 190-240 high.
If the temp is lower both set of numbers will read lower. And don't forget to have the fan going on the condenser, if that isn't running that will make the high side rise quite a bit.

[squelch]

This is a good article that says ambient temps should be above 84 degrees. This article is not 911 specific, but is very informative. I need to rebuild my compressor, so haven't followed his technique yet, but I will definitely give it a shot.

http://www.aircondition.com/wwwboard/alternative/current/7842.html

[marty2640]

As an HVAC/R tech the warmer the better for the vacuum but charg byweight to spec.will keep from cooking the compressor in the long run. mfg .weight should be listed in the manual or on label in compartment .

[mthomas58]

Originally Posted by squelch

This is a good article that says ambient temps should be above 84 degrees. This article is not 911 specific, but is very informative. I need to rebuild my compressor, so haven't followed his technique yet, but I will definitely give it a shot.

http://www.aircondition.com/wwwboard/alternative/current/7842.html

While I'm no expert this method of charging by "wetting" the condenser to cool it and reduce pressure/temps, presumably to accelerate the charge process seems a little risky. This method would seem to risk rapidly overcharging the system. Again no expert but I've done a lot of research and this first time I've seen it.

I've read numerous recommendations not to create an artificial environment such as using box fans to cool the condenser. Rather, close the deck lid and go slow and BE SAFE. None of us are getting out of here alive, but this is not how I want to go!

My 2 cents and thanks for the input.