Johnson Controls BQ 036, BQ 060 Pressure Drop Across Coil, Sequence Of Operations Overview

364985-XIM-B-0508

under field conditions would be inaccurate. To assure a dry coil, the compressors should be deac- tivated while the test is being run.

4.Knowing the pressure drop across a dry coil, the actual CFM through the unit can be determined from the curve in Pressure Drop vs. Supply Air CFM (Figure 13).

Failure to properly adjust the total system air quantity and static pressure can result in extensive system damage.

After readings have been obtained, remove the tubes and reinstall the two 5/16” dot plugs that were removed in Step 1.

NOTE: De-energize the compressors before taking any test measurements to assure a dry indoor coil.

	0.5
(IWG)	0.4		036	048	060
DROP	0.3
PRESSURE	0.2
	0.1
	0
	1000	1500	2000	2500	3000

FIGURE 13 - PRESSURE DROP ACROSS COIL

OPERATION

SEQUENCE OF OPERATIONS OVERVIEW

For these units, the thermostat makes a circuit between “R” and “Y1” for the cooling cycle.

The call is passed to the unit control board (UCB), which then determines whether the requested opera- tion is available and, if so, which components to ener- gize.

For heating, the thermostat makes a circuit between “R” and “W1”. The UCB energizes the compressor and condenser fan allowing the unit to run in heating mode. A time / temperature control operates the defrost cycle.

If at any time a call for both heating and cooling are present, the heating operation will be performed. If operating, the cooling system is halted as with a com- pletion of a call for cooling. Heating always takes prior- ity.

COOLING SEQUENCE OF OPERATION

CONTINUOUS BLOWER

By setting the room thermostat fan switch to “ON,” 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 ener- gized 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.

NO OUTDOOR AIR OPTIONS

When the thermostat calls for cooling, the low-voltage control circuit from “R” to “Y1” and “G” is completed. The compressor and condenser fan motor are ener- gized. After completing the specified fan on delay for cooling, the UCB will energize the blower motor.

Once the thermostat has been satisfied, it will de-ener- gize Y1. If the compressor has satisfied its minimum run time, the compressor and condenser fan de-ener- gize. Otherwise, the unit operates the cooling system until the minimum run time for the compressor has been completed. After the compressor de-energizes, the blower is stopped following the elapse of the fan off delay for cooling.

To be available, a compressor must not be locked-out due to a high or low-pressure switch or freezestat trip and the anti-short cycle delay (ASCD) must have elapsed.

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