AC Charging technique

[tjm]

After evacuating an AC system, should i open the high side port on the shrader valve (closing the high side port) when charging? The reason I ask is if I'm weighing the R134a going into the system from a scale (30 oz in my case). If the high pressure port is closed (shrader open) Im actually charging the red high pressure line of the gauge manifold.

 

[Ozymandias]

You dump it in the low side as there is enough room for it.
Don't worry about the pressure, it is much lower then what the system can take.
R-134a has only about 80psi at room temperature.

And charge it upside-down, liquid phase, otherwise it takes forever to load.
That's how it is done.

 

[tjm]

correct, thats what i do Ozy. Turn the 30lb can upside down, place on scale, charge from the low side. While doing this if I have my high side gauge attached to the hi side port and closed (shrader valve is open). I am then charging liquid freon into the high side line all the way to the manifold gauge. If my spec is 30 ounces of freon for a factory I'm think i should keep the high side shrader valve closed to get a proper fill.

 

[Ozymandias]

After you close the valve at the bottle wait till all the Freon has flashed inside the filling hose as it is part of the fill. It recondenses at the lowest part of the system at the same time.

 

[tjm]

I don't think I'm communicating properly.

The flow of r134a goes from the bottle to the low side AC port through the manifold gauge, through the AC system and back around through the high side port to the manifold gauge. Effectively filling the red hose at the end of the line.

do the factory fill specs take into account the amount of R134a left in the high side red hose after you've dispensed the proper weight of refrigerant? There seems to be quite a bit left in the high pressure manifold hose.

 

[Ozymandias]

Yes it is taken into account and it is only gas*, so the amount isn't that much.
And as long as the engine isn't running there is no high and low side pressure wise, it's all one circuit and the pressure is equally all around.

*the big amount of Freon sits liquid at the base of the system where the compressor is.
Liquid phase on the high side up to the orifice you only see with the engine running.

 

[Ozymandias]

That's why we fill under vacuum and upside down so the liquid phase is pulled right down deep into the system without flashing first which we try to avoid to to safe time.

 

[tjm]

I have to crank the engine to get a full fill, even after vacuum.

 

[Ozymandias]

No that doesn't sound regular.
Under vacuum it must suck the load right in through the low side port.

How long have had you run the vacuum pump? It needs a couple hours to get all the moisture out. Water evaporates under vacuum but it takes a lot of time to get it out of the whole system including drier and compressor(oil).

Steven told me a lot when we did my system..

 

[Ozymandias]

Also 29hg isn't enough.

Here is a list

You want to come down to at least 1000micron, better below.

 

[tjm]

then that means my vacuum pump doesn't suck enough. Or my manifold gauge isnt accurate enough

 

[Ozymandias]

Probably the pump, I had an Amazon single state, crapped out, sent it back.
Steve was looking for a decent one, starts at about 400$ dual stage, 1/2HP.

Seems JB industries has decent stuff that pulls down to 600micron.

 

[sag2]

At 86° you only need 28.67 to boil the water out. At 104° its 27.75. If the ambient is not high enough for your pump, get it good and hot with the hood closed to heat up everything.

 

[tjm]

I have a robinair 15310 - owners manual says it can pull down to 75 microns. I let the unit vacuum for 2 hours in mid 90's weather. robinair manifold gauges as well. Made in china like their pumps.

 

[Tuesdak]

I have to crank the engine to get a full fill, even after vacuum.

Unless you are using a A/C recovery machine that shoves it in with a press of a button on the high side... Sounds like you are charging from cans on the low side.

Yes, you need to run the engine to charge from cans. Be careful and charge slowly from upside down cans otherwise you can liquid slug the compressor. Your manifold gauge valve on the low side controls how fast you charge. IMO I keep the low side gauge under 60 psig when charging from a can. (The quality of your gauge set will show here re: if it's hard or easy to pull this off.) More or less bring the system up to pressure from the can, close valves, start engine, and then charge slowly from upside down can on low side only.

 

[Ozymandias]

Sounds good to me, you might want to check all connections then. Like said I struggled with my cheaper pump and tried to sort it out.
I've found several tiny leaks along the way, beginning at the connection right at the pump body and also the connections to the system itself.

If you can't go lower you probably have a leak somewhere.

 

[Ozymandias]

Unless you are using a A/C recovery machine that shoves it in with a press of a button on the high side... Sounds like you are charging from cans on the low side.

Yes, you need to run the engine to charge from cans. Be careful and charge slowly from upside down cans otherwise you can liquid slug the compressor. Your manifold gauge valve on the low side controls how fast you charge. IMO I keep the low side gauge under 60 psig when charging from a can. (The quality of your gauge set will show here re: if it's hard or easy to pull this off.) More or less bring the system up to pressure from the can, close valves, start engine, and then charge slowly from upside down can on low side only.

He says 30lbs bottle above.

 

[tjm]

I'll try another evac after i double check all seals.

 

[Tuesdak]

He says 30lbs bottle above.

Noted. It's the same instructions from a 30lbs bottle or can. One difference of note the 30lbs bottle is big enough to charge as a gas if one wants to reduce risk of liquid slugging a compressor.

I'll try another evac after i double check all seals.

With the cost of R134A today I suggest you start looking for a working used recovery machine. With this many evac and recharges as you are doing it will pay for itself quickly.

 

[tjm]

ok evac'ed, vacuumed, and recharged last night. still had to turn her over to complete the fill. I do have a recovery tank, robinair rg3, and an electronic scale to do all of this. Pretty simple to do if you have all the right equipment. If i had to buy it all again I would opt for some digital gauges, and a better vacuum pump. My specs says it will get the job done but at 3 CFM it might take a while to get down to 30 in of Hg.

This am, Ambient is 88 F went to run some errands, after 5 minute warm up i measured the driver and passengers side vents. They were both at 48F/49F. later today, ambient is 95 F. Truck sat in the sun for an hour. started her up, AC off, fan on low. Turned AC on. Pressure started to rise, FAN-PWM 0%. Pressure rose to 436 PSI. turned off AC and started moving. Couldn't really turn AC on again (traffic) until I was moving down the road and the FAN-PWM was > 0. Took about 5 minutes. everything settled down.