Lennox International Inc Lennox Air Handler, Merit CBX25UH Series Check-out Procedures, Operation

Check-out Procedures

NOTE - Refer to outdoor unit installation instructions for system start-up instructions and refrigerant charging instructions.

PRE‐START‐UP CHECKS

SIs the air handler properly and securely installed?

SIf horizontally configured, is the unit sloped up to 5/8 inch toward drain lines?

SWill the unit be accessible for servicing?

SHas an auxiliary pan been provided under the unit with separate drain for units installed above a finished ceiling or in any installation where condensate overflow could cause damage?

SHave ALL unused drain pan ports been properly plugged?

SHas the condensate line been properly sized, run, trapped, pitched, and tested?

SIs the duct system correctly sized, run, sealed, and insulated?

SHave all cabinet openings and wiring been sealed?

SIs the indoor coil factory‐installed TXV properly sized for the outdoor unit being used?

SHave all unused parts and packaging been disposed of?

SIs the filter clean, in place, and of adequate size?

SIs the wiring neat, correct, and in accordance with the wiring diagram?

SIs the unit properly grounded and protected (fused)?

SIs the thermostat correctly wired and in a good location?

SAre all access panels in place and secure?

CHECK BLOWER OPERATION

SSet thermostat to FAN ON.

SThe indoor blower should come on.

CHECK COOLING OPERATION

S Set thermostat to force a call for cooling (approximately 5ºF lower than the indoor ambient temperature).

SThe outdoor and indoor units should come on immediately.

SCheck the airflow from a register to confirm that the system is moving cooled air.

SSet the thermostat 5ºF higher than the indoor temperature. The indoor blower and outdoor unit should cycle off. Air handler should cycle off 45 seconds after the outdoor unit shuts off.

CHECK ELECTRIC HEATER (IF USED)

SSet thermostat to call for auxiliary heat (approximately 5°F above ambient temperature). The indoor blower and auxiliary heat should come on together. Allow a minimum of 3 minutes for all sequencers to cycle on.

SSet the thermostat so that it does not call for heat. Allow up to 5 minutes for all sequencers to cycle off.

Operation

TIME DELAY RELAY

Blower time delay operation:

1.When cooling demand is initiated, there is a 1 second motor-on delay.

2.After the motor-on delay expires, motor ramps up to 100% and runs at 100% until cooling demand is satisfied.

3.Once demand is met, motor runs at 100% for 45 seconds.

4.Motor ramps down to stop.

		3	4
1	2	100%	100%
		CFM	CFM
	1		OFF
SECOND		COOLING	45
DELAY
		DEMAND	SECS

Figure 14. Blower Time Delay

COOLING (COOLING ONLY OR HEAT PUMP)

When the thermostat calls for cooling, 24 volts is put on the blower time-delay relay coil and then the indoor blower relay energizes. The normally open contacts close, causing the indoor blower motor to operate. The circuit between R and Y is completed, closing the circuit to the contactor in the outdoor unit, starting the compressor and outdoor fan motor.

On heat pumps, circuit R and O energizes the reversing valve, switching the valve to the cooling position. (The reversing valve remains energized as long as the thermostat selector switch is in the COOL position.)

At the completion of the cooling demand the indoor blower and outdoor unit should cycle off. Air handler should cycle off 45 seconds after the outdoor unit shuts off.

HEATING (ELECTRIC HEAT ONLY)

When the thermostat calls for heat, the circuit between R and W is completed, and the heat sequencer is energized. A time delay follows before the heating elements and the indoor blower motor come on. Units with a second heat sequencer can be connected with the first sequencer to W on the thermostat subbase, or they may also be connected to a second stage on the subbase.

HEATING (HEAT PUMP)

When the thermostat calls for heating, 24 volts is put on the blower time-delay relay coil. Then normally open contacts close, causing the indoor blower motor to operate. The circuit between R and Y is completed, closing the circuit to the contactor in the outdoor unit, starting the compressor and outdoor fan motor.

If the room temperature should continue to fall, the circuit between R and W1 is completed by the second‐stage heat room thermostat. Circuit R-W1energizes a heat sequencer. The completed circuit will energize supplemental electric heat (if applicable). Units with a

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