Refrigerant help

I have a small pop cooler that runs but doesn"t get very cold. I can handle stuff like installing piercing valves, but I can"t read the gauges. I don"t get that stuff about Farenheit at a given PSI for a particular refrigerant. The system has 6.5 oz. of 134. 250 P.S.I. on the high side. What should the gauge read when it has the proper amount of refrigerant? Thanks, Fritz

Easiest way is small tube hot and big tube cold.Was the cooler changed to 134a?

(quoted from post at 22:01:21 03/26/13) I have a small pop cooler that runs but doesn"t get very cold. I can handle stuff like installing piercing valves, but I can"t read the gauges. I don"t get that stuff about Farenheit at a given PSI for a particular refrigerant. The system has 6.5 oz. of 134. 250 P.S.I. on the high side. What should the gauge read when it has the proper amount of refrigerant? Thanks, Fritz

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igh side doesn't tell you a lot about proper charge. Low side should read just about freezing....forget the pressure. A good indicator is that low side, large line as it exits cool compartment should be cold to touch, but not frozen & not so cold as to condense moisture & drip on your wife's floor. If icy or dripping condensation, let a little out. This is all with cool compartment at the temperature you plan on running all the time.

Best/CORRECT way would be to recover the refrigerant, then install the correct name plate amount. Need charging cylinder to do that.

That being said, the LOW SIDE pressure is what you want to be looking at to approximate a correct charge. Once the cooler has cooled down (still running, though), you should see a low side pressure in the 29 to 35 PSI range. As you begin to overcharge, low side pressure will go up and a line of condensation (or possibly frost) will appear on the compressor"s suction line and march towards the compressor as overchrage is increased.

The high side pressure IS important to look at to see if it is unusually high... could be from a dirty condensor, failed fan (if used), or impurities/air in the system

You mentioned installing line-piercing valves, you have just created several future leak points.
R134A Temp pressure chart

No, the information I gave was per the tag. Low side pressure not indicated. Bob observed that piercing valves will create leaks, but.... how else to tap the system?

Pro way is to silver braze a quality Shrader valve with a tight sealing brass cap onto the original charging pigtail, or use a special tool to charge through the OEM pigtail, then clamp it off and silver braze it shut as was done originally.

I can only attempt reading between the lines since you don't describe your"pop cooler"well enough to even know what you are working on.
If what you have is indeed a comercial drink machine you got on the cheap or free,it likly needs a compressor or is otherwise not worth repairing. If all you want is to store cold drinks and not have provisions for coin operated,free and low cost residential refrigerators are easy to find. 99 times out of 100 the problem is not lack of freon when small refrigeration units stop cooling right. I reccomend making certain there isn't some other problem before tapping the lines. If you insist on opening the system and recharging it,install a site glass and slowly recharge over 24 to 48 hours. No guage reading required and guaranteed precision charge. Sorry I can't be more spicific but I don't even know which type compressor and metering it has on it.

Fritz,
If you look, there is a temperature scale on the suction guage, sometimes it on the box the freon bottle comes in. Pop coolers and refrigerators, you want the temperature to be above freezing. Some guages the temp is in celcius. zero celcius = 32 F.

I think the suction pressure should be around 5 psi for 134A.

If you add too much freon, you will see the suction line at the compressor will frost up.

So add the freon slowly, there will be condensation on the suction like before it turns to frost.

This is ture with everything I"ve worked on. Too much freon, liquid will come back, freeze up at the compressor, wash the oil out of the compressor, and you can guess what will happen next.

George

The 250 psi high side is a test pressure and not what it should run at

First things first. 1 Clean the coils( both of them). Second the high side or condenser should be around 125 psi in a 70 degree environment. Low side 5-10 ish. Capillary tube systems do not work with sight glasses it will be over charged. You can charge by name plate either with a accurate weight scale or a charging cylinder. Do you have a vacuum pump and the other neccessary equipment like a micron gauge to tell if you have the moisture out? If the thermostat is set too low it could be freezing over and not cooling, if the condenser is plugged it will not cool either. They must be clean before adjusting refrigerant amounts. We get several each year here at the college and most of the time after routine maint the issues are leaks and dead compressors. To be thourough you need super heat and sucooling measurements to see if it is charged correctly. 12 ish for super heat and 8-10 for sub cooling. Much easier if I have my hands on it. We repair quite a few at the tech college here. Sorry for the long answer, Just adding refrigerant is not always the best answer.Also putting your gauges on may take enough refrigerant out to cause a low charge, be careful.
Roger

I plugged it in and the compressor and the fan both came on. I blew the dirt out the entire compartment and the air flow was better but still nothing. I don't think it's freezing up because from startup at room temperature, no part of the system even tried to get cold. Can the cold control be bad, even if the unit runs? There is a separate on-off switch for the compressor instead of incorporated into the cold control, never saw this before. I get what you're saying, I'm trying to eliminate all the external stuff before opening the unit. Thanks to you and all the others for your help. I like this kind of work and I'm slowly building my equipment arsenal, and reading anything I can on the subject.

The extra switch for the compressor should be wired in series with the compressor and cold control, so it can be serviced.If the condensing unit runs, the cold control is working. I have seen too many running too long without shutting of the condenser to let the evaporator de-ice because that fan should be on all the time. It does sound like the refirgerant has leaked out, the condenser should measure about 100 degrees in the center on a normal system. If it has ports on it the gauges should real 70ish when the unit is off on both sides of the system. I have seen too many that only have a low side access, you really need both. Has some one already tapped into it? If so it will be down at the condenser. Coke machines and similar old ones it is easy to slide the tray out with the evap, still attached by removing a couple plates. Checking temps with an accurate thermometer,(Themocouple)will get you in the ballpart for pressures if you can use the charts, Line from compressor to condenser real hot cooling to the 100 degrees in the middle. The evap has to operate below the box temperature or no colling will take place 10-25 degrees. If it all points to the refrigerant being low tap into it, off 70 ish just means you have refrigerant but not neccessarily enough.If it has leaked out you will need to find the leak and repari it. Depending on how long it has been sitting open will determine how long it need to be under a cacuum to get the moisture out wich can cause a lot of problems in a small system.Then it goes to having the correct equipment and being able to used it correctly.

R-134A uses a type of oil that breaks down under high temperature. If your condenser was clogged up overheating the compressor the cap tube is probably restricted not allowing enough refrigerant to flow through it.If you add a small amount of refrigerant to the system and the suction pressure does not increase the cap tube is probably your problem.
The suction pressure should be close to 17#. There will be a temperature difference of 10 to 15 degrees between refrigerant temperature and discharge air temperature.
The proper repair is to replace both compressor and cap tube.

Search 134A oil or 134A cap tube restrictions.