Cab A/C

[Sequim Guy]

Have a 1999 F-53, V-10 Thor Residency. Checked the cab A/C and felt it needed a shot of freon, went under the hood and found that it still had the sightglass on the dryer. Sure enough, there were a lot of bubbles, almost foam looking going through the sightglass. Even after adding 2 12oz cans of freon, it still looks foamy in the glass.
I know in the old days we added freon until the bubbles went away, is that the way to do it now? It has a huge condenser, so just how much freon can this thing hold. I still don't think it is blowing as cold as it should.
More freon or not?

Any help appreciated.

[subford]

There should be a sticker someplace maybe in a kitchen cabinet that tells what all the items are that are installed on your RV.
If you can not find the sticker call your RV Mfg. and ask them what brand they put in the RV for the dash A/C and where the items sticker is.

This will give you the brand and model of the dash A/C that you have.
Go to the A/C Mfg. site and it should tell you how much gas goes in your A/C unit.

[Sequim Guy]

Thanks for the ideas.
Will look for sticker, but RV mfg. went under 10 years ago.
Still wondering about using bubbles as a gauge to tell when system full.

Any A/C experts out there?

[bigskymt]

I'm no expert but I've done it your way until I bought guages at Harbor Freight.
Sometimes the system has to run several minutes at 1000 rpm or so for the bubbles to clear. 134 doesn't condense as well as R-12 did either so your condensor fan should be running and condensor clean when you're checking temps.
Thanks for your service 9th Inf., from the Americal.

[krivanj]

My a/c expert, who is really good, told me that if using 134a, it may be at perfect charge level but still making bubbles. No bubbles only worked with R12.

[Sequim Guy]

Thanks for the help, will not add any more freon now, will run it for a while and see what it does.
The bubble theory not working on 134a may explain why there was a black piece of paper stuck over the sightglass so you couldn't see the freon stream.
I took it off and thought I had outsmarted them............. "curses, foiled again".

[Topflite51]

You need a set of gauges if you are going to service your AC. Now, your AC could be overcharged and can be damaged. Actually, recommend a qualified AC specialist.

[Sequim Guy]

The hose I use has a gauge on it and it read in the middle of the "Filled" section on the gauge, nowhere near the "Overfilled/Danger" red section.
So it should be OK.

[TXiceman]

R12 or R134a should have a clear glass. My best advice to you is to first find the leak and then recharge the system. I would hire a trained tech to fix it right rather than chance several hundred dollars of potential repair cost if you do something wrong.

You also need to hold the engine at a high idle (1100 or 1200 RPM) for at least 5 minutes, with the AC fan on high speed and the RV doors and windows ope to keep the AC loaded and on.

ken

[Sequim Guy]

Thank you all for your advice.

Now, who is correct about the bubbles in 134a, krivanj or TXiceman???

[whem2fish]

question in 1999 was it r-12 if so get r-12a (freeze 12)

[TXiceman]

1999 should be R134a. An expansion valve for the unit is very difficult to size and make operate properly if you have 2 phase flow entering the valve. They are designed for liquid at the inlet. If there are bubbles, that is 2 phase flow.

Some of the small units operating on the blends (R400 series) will have a few bubbles, when converted from R-22.

Ken

[ga traveler]

I started servicing Ac's in the R12 era. When the 134A came along I had a heck of a time servicing. I finally got smart and went to our local AC service center and talked to them. You do not service till the bubbles stop, as you did with R12. It is much easier to overfill with R134A. Stay to the low side of the pressure band when servicing.

[TXiceman]

The units I have serviced all ran clear sight glosses. R-12 and R134a are both refrigerants with similar properties. I have designed a number of systems using R134a and you still have to have a clear liquid seal art the expansion device.

Refrigerant s change, but thermodynqmics and heat transfer do not. If yo are getting bubbles at the sight port and you are "full", there is some restriction up stream causing a pressure drop which causes the bubbles.

Have you ever tried to size an expansion device for 2 phase flow or flashing liquid entering the valve?

Mechanical engineer specializing in thermodynamics and many, many A/C units and refrigeration units over the past 41 years. I have designed them, serviced them, rebuilt them and started them up.

Ken