Any good refregertion techs out here?

nwtundra

I have a Beverage Air cooler running on 29 oz of R12.
What should be the correct low and high pressures?
HELP!

Kevinj

P/T chart

You need to give a little more information on the cabinet design and refer to a PT chart. With a chart you can convert any refrigerant. Weather it is R12or R134 the troubleshooting is still done the same way, you need to move gas through the system !

Floyd_5

It depends....

a little system like that will change pressures rapidly depending on the ambient temp. and the temp. inside the cooler. Hotter, higher.... cooler, lower.....

That being said, I would look for the low side to be in the 10-25 range and the high side to be in the 100-150 range.
Should get you in the ballpark.....

nwtundra

Thank you!
The cooler has an air cooled condenser on the bottom of the unit and the evaporator is mounted inside the case. It has 2 fans blowing cold air. I am getting 9 PSI on the suction and 110 on the high side (40 deg inside, 70 deg. outside). With the thermostat cranked up to the coolest setting the compressor shuts off with about 40 deg. inside the cooler. I can’t get it cooler!
I think it may be overcharged but I am not sure how to tell for sure. Thanks again. Jerry

JimGPE_8

Low suction, low head - sounds like it is a little under charged.

Having said that, if the temperature is not getting to what you want, what is shutting the compressor off? The thermostat? Safeties?

Get a meter and find out what is "opening" and shutting it off.

If the thermostat is shutting it off before the case gets to what the thermostat is set for, it is perhaps bad.

If it is a safety, perhaps that is bad, or perhaps your suction is low enough it is going off on low pressure.

There's something else going on here besides charge.

Floyd_5

Jump out the t-stat.....

bet that suckers the thing loseing charge in the cap tube...

Dan Law_2

Too warm in box

Where is the sensing capillary of the thermostat located?
Many small, self contained boxes utilize a thermostat that senses evaoprator temperature, rather than box space temperature. These thermostats (or "cold controls") function to not only control the box temp, but also to act as defrost control, by ensuring the evaporator always reaches a temp above freezeing before the unit it allowed to turn on, or "cut in" on each sucessive cycle. As you set the control "colder" you set only the cut off point - the cut in is always the same at a predetermined temp. The controls are known as "constant cut in" controls.

If your system is low on charge, then the associated low side pressure will be low as you indicate. (9 lbs R12 = aprox 9F) This means the section of evaoprator the DOES still have liquid refrigerant in it, it operating at a colder than ussual temp - right?

If the cold control sensing element is located on this still functiong section of evaporator, the unit will cycle off (because that section of coil is "cold" even though the box space temp has not yet reached it's desired point)

Once off, the coil will be forced to attain it's defrost or constant "cut in" temp (40F?) then cycle on again. Sounds to me this is your situation.

Ultimately, it's a low charge condition, meaning a leak. The thermostat or cold control is only doing what it is intended to do, albeit with an underperforming refrigeration system.

Get the numbers (all of them) from the cold control and get yourself to a good refrigeration supply house. They can confirm the control's cut in and cut out temps, therby giving you more insight for your diagnosis.