Frequently Asked Questions - Troubleshooting
You will not be able to judge what the unit is doing when an APR control is operating. You will need to isolate the control from the system with either a ball valve or solenoid valve (with manual stem) in the suction line between the outlet of the control and the "T" on the suction line. We recommend that isolation ball valves be installed on all connections to the APR Control device. Without these isolation valves the APR Control can mask several types of issues.
The APR Control is shipped from the Factory set for approximately 36 degrees F. evaporator coil temperature, or to start opening at 110psi (in an R-410A system). Most application will not require adjusting the APR Control. But, in some applications (especially with Humidity Control), if the runtime is inadequate or low load operation does not cause suction pressure to fall low enough, you may need to adjust the APR Control hot gas valve. Please call Rawal Devices Engineer’s (800-727-6447) at the factory prior to attempting any adjustment.
The bellows in the Hot Gas portion of the control will only withstand a certain amount of pressure. There are a number of causes for high pressure spikes in a system. If the system doesn't have some type of head pressure control the compressor can operate above the safe limits of the APR Control. Normally safeties are in place to prevent this (excessive bypass) if they haven't been compromised. High head pressure is caused by the following; overcharged, dirty or plugged condenser coils, non-condensables in the system and the loss of air flow. Whether air cooled or water cooled unit, anytime you lose the cooling medium the head pressure will rise. ANYTIME A HIGH HEAD PRESSURE OCCURANCE HAS HAPPENED THE CONTROL NEEDS TO BE CHECKED. THIS IS AN ABNORMAL CONDITION IN THE SYSTEM AND MANY COMPONENTS MAY BE AFFECTED.
First isolate the APR Control to see if you have an issue with system charge, evaporator expansion device, or some other system issue. If the system appears to be operating properly with the APR Control out of the circuit, then you will need to turn you attention to the control. Open isolation valves and allow the unit to go into deep modulation (usually best accomplished by reducing airflow across the evaporator coil). Check the compressor superheat at the desuperheater bulb (Is the desuperheater bulb located correctly?). The temperature of the suction gas entering the compressor should be maintained below 65 degrees F. If not, you may have an issue with the desuperheating injection valve. If the problem persists consult with engineers at Rawal Devices.
If you have checked all things related to the system such as condenser coil (clean?), charge, and other general maintenance items, then the first thing to check is the insulation on the bulb(s) from the control, most particularly the injection valve. The bulb insulation may have deteriorated or maybe insufficient for the ambient conditions you are dealing with. APR Control injection valve bulb must sense suction line temperature (between the APR Control mixed gas discharge tee into the suction line and the compressor) and not ambient.