Frequently Asked Questions about the APR


Welcome to the FAQ section of Rawal Devices. Below you will find answers to common questions about our APR Control solution, application & installation challenges, troubleshooting & service and more. If you can’t find what you are looking for, please contact us and we will be glad to assist you! Rawal Devices is particularly proud of our customer service availability and knowledge! Call us!

Most Popular FAQ’s


Application

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How does the APR Control work?

As the heat content of return air drops, the suction pressure drops opening the compression ratio reduction valve (CRR) of the APR Control. The discharge gas gets sent into the desuperheat chamber then back to the suction line. A liquid injection valve mixes liquid with the discharge gas (in the desuperheat chamber) when the mixed gas temperature rises to 60F.

The APR Control derates the evaporator coil capacity extending the run time while keeping the active portion of the coil at a  temperature below dewpoint of the entering air, thereby dehumidifying during the extended run period.

I have a humidity issue - what do I do?

Before you call Rawal Devices, we will need the following basic information; including equipment information, equipment cycle times, general building and space information, what you believe is possibly causing the humidity issue, and outdoor climate. It is likely that the APR Control could provide a simple and cost effective solution.

The air conditioning system is Short Cycling – how can the APR help?

Often systems will short cycle either as a result of being oversized from the beginning, or simply because the load varies too much during the air conditioning operating season. The APR Control will often be employed to help reduce system capacity and extend runtimes, but the installer must confirm that suction pressure will fall far enough to cause the APR Control to begin to modulate the system capacity. If load does not fall enough, the APR Control may not be helpful in that specific application. Please refer to adjusting the APR Control, in the Start-up section of this FAQ.

Selection

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Why is selection so important?

The designer and installing contractor must ensure proper oil return from the evaporator coil in the system. All forms of modulation that change the velocity of the suction gas have this concern. We insure this is not an issue by maintaining a minimum velocity up the risers.

How are the APR Controls classified?

The APR Controls are classified by refrigerant and the maximum amount of modulation. Thus an APR-410-1 gives 1.5 tons of modulation on an R-410A system. Please note that the capacity listed on the APR is the modulation capacity not the system capacity. 100% modulation is NEVER acceptable. Example: a 3.5 ton system cannot use the APR-410-3 (3.5 tons of modulation).

What is the meaning of the model number on an APR Control?

The APR Controls are classified by refrigerant and the maximum amount of modulation. Thus an APR-410-1 gives 1.5 tons of modulation on an R-410A system. Please note that the capacity listed on the APR is the modulation capacity not the system capacity. 100% modulation is NEVER acceptable. Example: a 3.5 ton system could not use the APR-410-3 (3.5 tons of modulation).

Installation

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Are there additional materials needed to install the control?

Yes, you will need at least three “T’s” or someway of connecting the APR Control to the system suction line, liquid line, hot gas line and the external equalizer line where necessary. In addition, isolation ball valves are required. Without the ability to isolate the APR Control from the circuit there may be NO WAY TO CHARGE OR CONDUCT SYSTEM DIAGNOSTICS.

Do I need to mount the control?

Yes, vibration resulting from the operation of the compressor could put strains on the piping and control. A simple mount to either the cabinet or a stand is all that is needed.

Is the APR Control sensitive to how it is positioned?

Yes, the APR Control can only be mounted in such a way that the Schrader/access valve is located down and the mixed gas discharge to the suction outlet up. ANY OTHER POSITION OR ORIENTATION IS UNACCEPTABLE AND WILL LEAD TO SYSTEM PROBLEMS AND LIKELY DAMAGE.

Start-up Procedures & Adjustment

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I have installed the APR Control; now what are the steps I need to take after evacuating the system?

Make sure the APR Control was open to the circuit during evacuation. Prior to charging the system you should isolate the APR Control out of the system with the three isolation valves (closed). You will need to have the APR Control isolated during the charging of the system and the system should be run initially with the APR Control entirely out of the circuit (isolation valves remain closed). This is necessary to make sure the charge is correct and that the air conditioning system is operating as originally designed, and so there is a baseline to measure the system “with the APR Control modulating” against. In addition, there is the benefit of allowing the system filter/dryer to clean the refrigerant before it is allowed to enter the APR Control. This helps ensures for the cleanest startup possible.

Will I need to adjust the APR Control?

The APR Control is shipped from the Factory set for approximately 40 degrees F. evaporator coil temperature, or to start opening at 118psi (in an R-410A system). Most application will not require adjusting the APR Control. But 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.

Is there any adjustment required for the desuperheating injection valve?

No, NORMALLY YOU WILL NEVER TOUCH THE INJECTION VALVE. If you believe there is any need to adjust the desuperheating injection valve, please call Rawal Devices Engineer’s (800-727-6447) at the factory prior to attempting any adjustment.

Troubleshooting

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The AC unit is not operating correctly, how do I troubleshoot with an APR in the system?

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.

Will I need to adjust the APR Control?

The APR Control is shipped from the Factory set for approximately 40 degrees F. evaporator coil temperature, or to start opening at 118psi (in an R-410A system). Most application will not require adjusting the APR Control. But 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.

APR Control appears to be bypassing all of the time?

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.