Compressors are designed for a specific evaporator temperature range. A compressor designed to refrigerate a walk-in cooler would be misapplied if used to pull the temperature down in the walk-in freezer. And, likewise, a compressor designed for a walk-in freezer would be overwhelmed trying to pull down both the walk-in cooler and freezer simultaneously.

The manufacturer’s solution often is the CPR valve. The valve will simulate the operating pressure of a walk-in freezer, thus not overloading the compressor, which is designed for a walk-in freezer. Eventually, the walk-in cooler will reach the desired temperature, at which point the evaporator pressure regulator will, for the most part, prevent any further flow of refrigerant. Once that is accomplished, the compressor, or in this case, compressors, which are designed to take the temperature down to freezing, can do just that in your walk-in freezer. I suspect you will find that you have a CPR valve that is malfunctioning or is out of adjustment, causing reduced refrigeration capacity.

Once you have adjusted or replaced the CPR valve, begin with an initial setting of 10 psi, then adjust higher or lower until the compressors are pulling just below nameplate amperage.

Compound Gauges

From Wallace Martina Tucson, AZ

Are compound gauges (service manifolds) sufficient to properly evacuate a system? In addition, do you evacuate through both high- and low-side gauges? Hooked up to each service port?

If the answer is yes, does this not put a strain on the high-side gauge needle by pulling it into a vacuum? Also, would you recommend removing the valve stems on the service ports to pull a faster vacuum?

Is it safe to use your nitrogen regulator to pressure test with carbon dioxide?

Answer:

By Gene Silberstein Whiteside, NY

In response to your question, compound gauges are sufficient to properly evacuate a system. However, with the EPA regulations regarding system leak rates and proper vacuum levels, compound gauges are no longer sufficient to properly evaluate the vacuum that is being pulled on the system. In conjunction with the compound gauges, a micron gauge, or electronic vacuum gauge, should be used when evacuating an air conditioning or refrigeration system. Micron gauges will indicate even the smallest of leaks while a compound gauge may not.

It is good field practice to pull the best possible vacuum on a system. Unfortunately, there are many restrictions that are present throughout the system that affect the evacuation process. A few of these restrictions are metering devices, flow check valves, evaporator pressure regulators, liquid line solenoid valves and compressor flapper or reed valves.

For this reason, it is good field practice to evacuate a system from both the high and low sides of the system. It is also good field practice to make certain that any solenoid valves in the system are energized (open) in order to allow the system to evacuate properly.

If you are doubtful that all areas of the system are being evacuated, draw a piping diagram including all valves and indicate whether or not they are open. This will help determine if all parts of the system are being evacuated. Don’t worry about damaging the high-side gauges on the manifold, since the evacuation process will not have a negative effect on them.

In order to speed up the evacuation process, the pins on Schrader valves can be removed. However, a special tool must be purchased which will allow the stems to be replaced without allowing atmosphere to be sucked into the system. This tool is connected directly to the Schrader port and your hoses are connected to the tool. Once evacuation is complete, the pin is installed and the device is removed. If the pins are to be removed from the high and low sides of the system, two pin removal tools will be needed.

In response to the last part of your question, you cannot use a nitrogen regulator on a carbon dioxide tank! Even though the threads may appear to be similar they are not. The nitrogen regulator has an angled fitting similar, to a flare connection, while the carbon dioxide regulator has a square fitting with a gasket similar to a washing machine hose. Therefore, the seal is not a good one. Besides, if you already have a nitrogen regulator, why not just use nitrogen? It’s about 1/2 the price of carbon dioxide and you don’t need to purchase the regulator.

Old Refrigerator

From Alvertis Bledsoe Marianna, AR

I have a General Electric monitor top refrigerator that is more than 50 years old. The nameplate shows sulfur dioxide was in it. The compressor still works, but there is a hole in the coil due to rust.

I want to know how I can restore this unit. Since sulfur dioxide is no longer available, can I use another refrigerant?

Answer:

By Jack Healy

Past International President, RSES

Colorado Springs, CO

Repair the hole in the coil by soldering or using epoxy. Then replace the drier with a small pencil-type drier. Pull a good vacuum in the cooling system, then recharge the system with R-12.

Charge until the suction side reaches a 0° pressure reading. This pressure will depend on the altitude and temperature of your part of Arkansas.