Customer Service

Support & Troubleshooting for Commercial Refrigeration Systems

This section is divided into two main sections, high side and low side. There are links to our Tech Topics bulletins for more in-depth information. Our goal is to provide helpful suggestions for your refrigeration troubleshooting needs. Please feel free to send your own suggestions to hrpd.feedback@heatcraftrpd.com for possible inclusion in a future update. If you need technical assistance, please send an e-mail to sesweb@heatcraftrpd.com. Please include your name, address, and daytime phone number.

High Side

Q. I have frequent or infrequent oil pressure failures requiring a manual reset. The oil pressure on restart appears normal. What causes this?

A. Here is a general listing of possible causes of oil failure trips:

To learn more about this subject, click on Oil Pressure Problems in Refrigeration Systems (Tech Topics, Vol. 3, No. 1, January, 1995)

 

Q. How does evaporator superheat affect oil return or cause oil pressure failures? If my return gas is superheated how can I still have liquid?

A. Superheat generally does not affect actual oil return to the compressor crankcase unless the superheat is set so high that it caused a starved condition resulting in low return gas velocity or evaporator icing. Low superheat at the compressor results in liquid refrigerant being present in the oil sump. The violent action of liquid refrigerant boiling in the crankcase will cause oil to be blown out into the system resulting in low oil levels. Liquid refrigerant in the compressor’s pressurized lubrication system will result in a loss of net oil pressure resulting in an oil failure trip, bearing damage due to the loss of lubrication to bearing surfaces and possible valve damage to due liquid slugging caused by the returning oil.

To learn more about Superheat, click on Principles of Refrigeration Superheat (Tech Topics, Vol. 1, No. 2, June, 1993)

 

Q. I have a 3-way valve at the condenser to control my high side pressure. How does this valve work?

A. The 3-way valve you are referring to is called a headmaster. The headmaster maintains a minimum liquid pressure at the receiver by injecting hot gas on the liquid surface and by stacking liquid refrigerant in the condenser thereby reducing the condenser capacity during low ambient conditions.

To learn more about headmasters, click here.

 

Q. How does the ORI / ORD work?

A. The 3-way valve has horsepower limitations. Larger units produce mass flows much high than the capacity of the largest 3-way valve. In these situations a Dual valve System is used to maintain a minimum discharge pressure. The Dual Valve System uses an Open on Rise of Inlet Pressure Valve (ORI) and an Open on Rise of Differential Pressure Valve (ORD)

To Learn more about the ORD/ORD, click on The Dual Valve System ORI/ORD.

 

Q. If I use a headmaster or ORI/ORD for head pressure control do I also need a heated insulated receiver?

A. Head pressure control and the use of a heated Insulated receiver are two separate subjects. Climatic Conditions dictate the use of mechanical head pressure controls. Application and calculated run times (based on expected winter load) dictate whether to use the heated insulated receiver option.

If extended winter off cycle periods are expected even in mild climates then a heated Insulated Receiver may be an option to consider. For example an outdoor walk in cooler in northern Kentucky may require a heated insulated receiver due to extended off cycle periods in the winter months due to low product loads rather than winter design temperatures for that area. On the other hand, a walk in freezer in the same area sized for an 18 hour run time and heavy winter product loads may not require a heated insulated receiver since it will not be subjected to extended off cycle periods.

To learn more about heated insulated receivers, click here.

 

Q. Why do you use mechanical head pressure controls when condenser fan cycling is an option? Does fan cycling have limitations?

A. Condenser fan cycling does have limitations. Most compressors require airflow from the condenser for compressor cooling. A condensing unit having only one condenser fan motor would not be a good candidate for pressure fan cycling since the condenser fan could be off for extended periods of time.

Another consideration is the affects of wide pressure swings on the TEV since liquid pressure is an opening force of the valve.

To learn more about Pressure Fan Cycling, click on Pressure Fan Cycling.

 

Q. What is the proper method to cycle condenser fan?

A. A. When fans cycle too rapidly, the condenser does not have sufficient time to stabilize and often, the controls overshoot the set points. Large swings in temperature can shorten the life of any condenser. Typically a 20 psig minimum differential is a good starting base line. You may have to adjust up from this point considering that fan cycling in excess of three minutes is considered excessive.

To learn more about condenser fan cycling control points, click on Condenser Fan Cycling control points (Tech Topics, Vol. 2, No. 1, May, 1994)

 

Q. How do I prevent compressor short cycling to widely varying load conditions?

A. There are several options to consider depending on horsepower, type of compressor and the severity of the load variations. The simplest for minor variations is to increase the dead band of the room thermostat. Other options include sizing the equipment to that they come on line in stages to maintain the desired box temperature. Wider load variations can be best controlled through capacity control. This includes hot gas bypass and or mechanical unloaders to balance the system capacity to the load.

To learn more about capacity control, click on Capacity Control Tech Topics.

 

Q. Due to site requirements I need a horizontal discharge condenser. Do I need to watch out for any special considerations?

A. There are too many variables to allow for a short answer. Please refer your concerns to an Application Engineer.

To learn more about horizontal condenser applications, click on click here.

 

Low Side

Q. My customer complains that his product temperature is not where it needs to be. I installed a recording thermometer and the temperature log indicated the box has reached the required room temperature. Have I missed something here? How is this possible?

A. Maybe you missed air throw and air distribution. Evaporators are intended to be Non-ducted but airflow and throw is an important factor to consider. Usually unstable product temperatures are directly related to Evaporator coil selection, airflow restrictions and air throw.

To learn more about non-ducted airflow with unit cooler, click here.

 

Q. I just installed a new evaporator. I’m having wide expansion valve swings preventing me from setting superheat and I have uneven frost patterns. My expansion valve is sized correctly. I’m out of ideas.

A. These are typical symptoms of an improperly selected nozzle. Liquid temperature at the expansion valve not only affects nozzle selection but also affects the TEV selection since colder liquid has more capacity. Typically nozzles and expansion valves are selected based on the BTU capacity of the condensing unit divided by the number of evaporators, 95°F. ambient and 105°F. condensing with a 90°F. to 95°F. degree liquid temperature. If the liquid temperature or the design condition change the selection may not be correct for the application. Consult an Application Engineer.

To learn more about refrigerant distribution and the affects of liquid temperature, click here.

 

Q. My evaporator feeds okay for a while then the suction pressure drops to the point the low-pressure switch cycles the compressor off. For some reason the blockage clears on its own then repeats itself. I have changed the expansion valve but I still have the same problem. Is it possible to get two bad expansion valves in a row?

A. Chances are there was nothing wrong with the original valve. All indications point to a wet system. The expansion valve will feed until the saturated suction temperature reaches 32F the freezing point of water. The wet refrigerant and oil will block the TXV until the internal temperature reaches the melting point and the blockage clears. The remedy is good service and installation practices to ensure a clean dry system. Recover the refrigerant, replace the driers and oil if its POE, evacuate to 500 microns or less and recharge. This problem should go away provided the system is clean and dry.

To Learn more about evacuation, click here.

 

To Learn more about successful installations, click here.