John Tomczyk

This article deals with low ambient head pressure controls containing charged domes. Their function is to keep a proper condensing pressure at the metering device for proper feeding of the evaporator. This is the second of a two-part series that began in the May 7 issue.

This article deals with head pressure control valves that work in conjunction with one another in cold ambient conditions. They keep the proper condensing pressure at the metering device for proper feeding of the evaporator.

The air filter protects the evaporator from dirt and lint. This article will explore how a dirty air filter can restrict airflow over the evaporator and cause very serious and expensive system problems.

Oil has a very low vapor pressure. Refrigerant will flow to it whether the refrigerant is in vapor or liquid form.

John Tomczyk's Jan. 8 column covered refrigerant gas density coming into a compressor’s cylinder from the suction line and how it is affected by temperature, how refrigerant density affected compressor capacity, and refrigerant mass flow rate through the compressor. This article covers how system pressures affect compressor capacity.

The service technician cannot control many factors that affect a reciprocating compressor’s capacity. However, the tech can control a few factors that can help the system have more capacity and run more efficiently.

Let’s say one of your customers has been complaining for three weeks of warm products in a low-temperature, glass door reach-in freezer. The store owner inspects the thermometers in the case and notices that the temperature will not pull down below 15°F.

Compressor overheating is still today's most serious field problem. It is caused by high compression ratios that are a combination of high condensing (head) pressures and low evaporating (suction) pressure.

Positive Temperature Coefficient Resistors (PTCRs) are variable resistors that vary their resistance when their surrounding temperature changes. Because they have a positive temperature coefficient, as their temperature increases so does their resistance. Also, as their temperature decreases, so does their resistance.

Current starting relays are used on single-phase, fractional horsepower motors requiring low starting torque. Their main function is to assist in starting the motor. Start and run capacitors can be used in conjunction with current relays to boost both starting and running torque.