System Functions and Sequence of Operation

Airflow Selection for Variable Speed Furnaces

The variable speed furnaces provide blower operation to match the capacities of the compressor during high and low stage cooling operation. The furnace control board allows the installing technician to select the proper airflows for each stage of cooling. Below is a summary of required adjustments. See furnace installation instructions for more details:

1.Turn SW1--5 ON for 400 CFM/ton airflow or OFF for 350 CFM/ton airflow. Factory default is OFF.

2.The A/C DIP switch setting determines airflow during high stage cooling operation. Select the A/C DIP switch setting corresponding to the available airflow shown in the furnace Installation Instructions that most closely matches the re- quired airflow shown in the air conditioning Product Data for HIGH speed.

3.The CF DIP switch setting determines airflow during low stage cooling operation. Select the CF DIP switch setting corresponding to the available airflow shown in the furnace installation instructions that most closely matches the re- quired airflow shown in the air conditioning Product Data for LOW speed. If a higher or lower continuous fan speed is desired, the continuous fan speed can be changed using the fan switch on the thermostat. Refer to the furnace Installa- tion Instructions for details of how to use this feature.

Airflow Selection for FV4C Fan Coils

The FV4 provides high- and low-stage blower operation to match the capacities of the compressor at high- and low-stage.

To select recommended airflow, refer to the FV4C Installation Instructions. The FV4C utilizes an Easy Select control board that allows the installing technician to select proper airflows. This fan coil has an adjustable blower-off delay factory set at 90 sec. for high- and low-stage blower operation.

Install Electrical Accessories

Refer to the individual instructions packaged with kits or accessories when installing.

Start-Up

!CAUTION

UNIT OPERATION AND SAFETY HAZARD

Failure to follow this caution may result in personal injury, equipment damage or improper operation.

S Do not overcharge system with refrigerant.

S Do not operate unit in a vacuum or at negative pressure. S Compressor dome temperatures may be hot.

!CAUTION

PERSONAL INJURY HAZARD

Failure to follow this caution may result in personal injury.

Wear safety glasses, protective clothing, and gloves when handling refrigerant and observe the following:

S Front seating service valves are equipped with Schrader valves.

SYSTEM FUNCTIONS AND SEQUENCE OF OPERATION

The 127A models utilize a 2-stage cooling indoor thermostat. With a call for first stage cooling, the outdoor fan and low-stage compressor are energized. If low-stage cannot satisfy cooling demand, high-stage is energized by the second stage of indoor thermostat. After second stage is satisfied, the unit returns to low-stage operation until first stage is satisfied or until second stage is required again.

When both first stage and second stage cooling are satisfied, the compressor will shut off. Therefore, with first stage of cooling Y1 is powered on; and with second stage of cooling Y1 and Y2 are powered on. When a 2-stage unit is operating at low-stage, system vapor (suction) pressure will be higher than a standard single-stage system or high-stage operation.

Compressor Operation on 127A Models

The basic scroll design has been modified with the addition of an internal unloading mechanism that opens a by-pass port in the first compression pocket, effectively reducing the displacement of the scroll.

The opening and closing of the by-pass port is controlled by an internal electrically operated solenoid. The modulated scroll uses a single step of unloading to go from full capacity to approximately 67% capacity. A single speed, high efficiency motor continues to run while the scroll modulates between the two capacity steps. Modulation is achieved by venting a portion of the gas in the first suction pocket back to the low side of the compressor, thereby reducing the effective displacement of the compressor. Full capacity is achieved by blocking these vents, thus increasing the displacement to 100%.

A DC solenoid in the compressor controlled by a rectified 24 volt AC signal in the external solenoid plug moves the slider ring that covers and uncovers these vents. The vent covers are arranged in such a manner that the compressor operates at approximately 67% capacity when the solenoid is not energized and 100% capacity when the solenoid is energized. The loading and unloading of the two step scroll is done “on the fly” without shutting off the motor between steps.

NOTE: 67% compressor capacity translates to approximately 75% cooling capacity at the indoor coil.

Follow these steps to properly start up the system:

1.After system is evacuated, fully back seat (open) liquid and vapor service valves.

2.Unit is shipped with valve stem(s) front seated (closed) and caps installed. Replace stem caps after system is opened to refrigerant flow (back seated). Replace caps finger-tight and tighten with wrench an additional 1/12 turn.

3.Close electrical disconnects to energize system.

4.Set room thermostat at desired temperature. Ensure that set point is below indoor ambient temperature and is set low enough to energize desired stage. In order to start the system in low stage, refer to the literature for the installed thermo- stat and adjust the set point so that the differential between the room temperature and the set temperature energizes Y1.

5.Set room thermostat to COOL and fan control to ON or AUTO mode, as desired.

6.Operate unit for 15 minutes. Verify system refrigerant charge by measuring the sub-cooling for low stage and comparing with the published sub-cool on the rating plate.

7.In order to switch the the system to high stage, refer to the literature for the installed thermostat and adjust the set point to a lower value so that the differential between the room temperature and the set temperature energizes Y2. Verify system refrigerant charge by measuring the sub-cooling for high stage and comparing with the published sub-cool on the rating plate.

127A