Carrier 38BYC, 38BYG instruction manual Sequence of Operation, Cooling, Defrost, Heating

4.Set room thermostat to desired temperature. Be sure set point is below indoor-ambient temperature.

5.Set room thermostat to HEAT or COOL and fan control to ON or AUTO mode, as desired. Operate unit for 15 minutes. Check system-refrigerant charge.

SEQUENCE OF OPERATION

NOTE: Defrost-control board may be equipped with 5-minute lockout timer that may be initiated upon any interruption of power.

With power supplied to indoor and outdoor units, transformer is energized.

COOLING

On a call for cooling, thermostat makes circuits R-O, R-Y, and R-G. Circuit R-O energizes reversing valve, switching it to cooling position. Circuit R-Y energizes contactor, starting outdoor-fan motor and compressor circuit. R-G energizes indoor unit-blower relay, starting indoor-blower motor on high speed.

When thermostat is satisfied, its contacts open, de-energizing the contactor and blower relay. Compressor and motors should stop.

NOTE: If indoor unit is equipped with a time-delay relay circuit, the blower runs an additional 90 sec to increase system efficiency.

outdoor temperature falls below setting of outdoor thermostat (field-installed option), contacts close to complete circuit and bring on second bank of supplemental electric heat.

When thermostat is satisfied, its contacts open, de-energizing contactor and relay. All heaters and motors should stop.

DEFROST

The defrost control is a time/temperature control which includes a field-selectable (quick-connects located at board edge) time period between defrost cycles (30, 60, or 90 minutes), factory set at 90 minutes.

The electronic timer and defrost cycle start only when contactor is energized and defrost thermostat is closed.

Defrost mode is identical to cooling mode except that outdoor-fan motor stops and second-stage heat is turned on to continue warming conditioned space.

To initiate defrost, the defrost thermostat must be closed. This can be accomplished as follows:

1.Turn off power to outdoor unit.

2.Disconnect outdoor-fan motor lead from OF2 on control board. (See Fig. 10.) Tape lead to prevent grounding.

HP THERMOSTAT

24 VAC HOT	R
24 VAC COM	C
HEAT STAGE 2	W2
COOL/HEAT
	Y
STAGE 1
INDOOR FAN	G
RVS COOLING	O
EMERGENCY
	E
HEAT

TYPICAL	HEAT
FAN COIL	PUMP
R	R
C	C
W2 *	W2
E *
W3 *	Y
G
	O

*IF AVAILABLE

Fig. 9—Generic Wiring Diagram

A02325

(See Thermostat Installation Instructions for wiring specific unit combinations.)

LEGEND

24-V FACTORY WIRING

24-V FIELD WIRING

FIELD SPLICE CONNECTION

ODT

	OUTDOOR THERMOSTAT
EHR	EMERGENCY HEAT RELAY
SHR	SUPPLEMENTAL HEAT RELAY

A97413

HEATING

On a call for heating, thermostat makes circuits R-Y and R-G. Circuit R-Y energizes contactor, starting outdoor-fan motor and compressor. Circuit R-G energizes indoor-blower relay, starting blower motor on high speed.

Should temperature continue to fall, R-W2 is made through second-stage room-thermostat bulb. Circuit R-W2 energizes a relay, bringing on first bank of supplemental electric heat and providing electrical potential to second heater relay (if used). If

3.Restart unit in heating mode, allowing frost to accumulate on outdoor coil.

4.After a few minutes in heating mode, liquid-line temperature should drop below closing point of defrost thermostat (ap- proximately 30°F).

5.Short between speed-up terminals with a flat-blade screw- driver. (See Fig. 10.) This reduces the timing sequence to 1/256th of original time. (See Table 3.)

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