Sequence of Operation

430645-YIM-D-0610

Operation

Unit Control Overview

This series of heat pumps come factory equipped with Simplicity™ controls to monitor all unit functionality and safety controls.

Safety Controls

The Simplicity™ control board incorporates features to monitor safety circuits as well as minimize compressor wear and damage. An anti-short cycle delay (ASCD) is utilized to prevent operation of a compressor too soon after its previous run. The ASCD is initiated on unit start-up and on any compressor reset or lockout.

The Simplicity™ control board monitors the following inputs for each cooling system:

•A high-pressure switch is factory installed to protect against excessive discharge pressure due to a blocked condenser coil or a condenser fan motor failure. During cooling operation, if a high-pressure limit switch opens, the Simplicity™ control board will de-energize the associated compressors and initiate the 5-minute ASCD. If the call for cool is still present at the end of the ASCD, the control board will re-energize the halted compressor. If a high-pressure switch opens three times within two hours of operation, the Simplicity™ control board will lockout the associated system compressors and will flash an error code (see Table 11).

•A low-pressure switch to protect the unit against excessively low suction pressure is standard on all condensing units. If the low-pressure switch opens during normal operation, the Simplicity™ control board will de- energize the compressor, initiate the ASCD, and shut down the condenser fans. On startup, if the low-pressure switch opens, the Simplicity™ control board will monitor the low-pressure switch to make sure it closes within one minute. If it fails to close, the unit will shut down the associated compressor and begin an ASCD. If the call for cool is still present at the end of the anti-short cycle time delay, the control board will re-energize the halted compressor. If a low-pressure switch opens three times within one hour of operation, the Simplicity™ control board will lock-out the associated compressor and flash an error code (see Table 11).

•An ambient air switch will lock out mechanical cooling at 40°F. If the product was equipped from the factory with the low ambient option the unit will operate down to 0°F. If the unit was not ordered with the factory low ambient option a field installed low ambient kit is available.

The refrigerant systems are independently monitored and controlled. On any fault, only the associated system will be affected by any safety/preventive action. The other refrigerant system will continue to operate unless it is affected by the fault as well.

Compressor Protection

In addition to the external pressure switches, the compressors also have inherent (internal) protection. If there is an abnormal temperature rise in a compressor, the protector will open to shut down the compressor. The UCB incorporates features to minimize compressor wear and damage. An Anti-Short Cycle Delay (ASCD) is utilized to prevent operation of a compressor too soon after its previous run. Additionally, a minimum run time is imposed any time a compressor is energized.

The ASCD is initiated on unit start-up and on any compressor reset or lock-out.

Flash Codes

The UCB will initiate a flash code associated with errors within the system. Refer to UNIT CONTROL BOARD FLASH CODES Table 11.

Reset

Remove the call for cooling, by raising thermostat setting higher than the conditioned space temperature. This resets any pressure or freezestat flash codes. Simplicity™ only has minimum run time in cool. Heat pump mode shuts off immediately.

Continuous Blower

By setting the room thermostat to “ON,” the low voltage control circuit from the “R” to “G” is completed and the supply air blower will operate continuously.

Intermittent Blower

With the room thermostat fan switch set to “AUTO” and the system switch set to either the “AUTO” or “HEAT” settings, the blower is energized whenever a cooling or heating operation is requested. The blower is energized after any specified delay associated with the operation.

When energized, the indoor blower has a minimum run time of 30 seconds. Additionally, the indoor blower has a delay of 10 seconds between operations.

Cooling Sequence Of Operation

Single-Stage Heat Pump (PC090)

A single stage thermostat is required to operate the heat pump in cooling mode.

The reversing valve is energized during cooling mode. A continuous 24V signal is passed through the normally closed contacts of relay RY2 to the "O" terminal of the Defrost Control Board (DC). The normally closed relay DR-2 within DC energizes the solenoid (SOL) of the reversing valve.

When the thermostat calls for cooling (Y1), the Simplicity control board (UCB) closes the coils of relay RY1 and contactor

18	Johnson Controls Unitary Products

PC090 THRU 240, PD 180 THRU 240 specifications

Johnson Controls has long been a leader in the HVAC and building efficiency industry, and the Johnson Controls PC090 THRU 240 and PD 180 THRU 240 series of commercial rooftop units exemplify their commitment to innovation and energy efficiency. These units are designed to provide optimal performance for a wide range of commercial applications, ensuring comfortable indoor climates while maintaining energy savings.

One of the standout features of the Johnson Controls PC and PD series is their advanced cooling and heating capabilities. Both series can operate efficiently across a varied range of capacities, typically from 90,000 to 240,000 BTU/h for the PC series and 180,000 to 240,000 BTU/h for the PD series. This versatility allows users to select the most appropriate unit size for their specific needs, optimizing performance without wasting energy.

The technology behind these rooftop units includes advanced inverter-driven compressors that enable variable-speed operation. This feature allows for precise temperature control, resulting in enhanced comfort and reduced energy usage. The units also integrate smart controls that enable easy monitoring and management, ensuring that the HVAC system can adapt to changes in occupancy or external weather conditions.

Another notable characteristic of the Johnson Controls rooftop units is their robust construction and reliability. Designed for outdoor use, these units can withstand harsh weather conditions while maintaining operational efficiency. They are equipped with corrosion-resistant materials and protective enclosures to prolong the life of the equipment.

The units are also engineered with eco-friendliness in mind, utilizing refrigerants with low global warming potential to minimize their environmental impact. Furthermore, their energy-efficient designs often qualify for various energy incentives, providing businesses an additional return on investment.

Ease of installation and maintenance is another hallmark of the PC and PD series. With a modular design, these units can be easily transported and installed. Maintenance tasks are simplified, allowing facility management teams to perform regular service checks efficiently and effectively.

Overall, the Johnson Controls PC090 THRU 240 and PD 180 THRU 240 series stand out in the commercial HVAC market due to their flexibility, advanced technology, and dedication to energy efficiency and environmental responsibility. These units not only meet modern energy codes but also contribute to a sustainable future with their innovative features and reliable performance.