Bryant R-22 service manual VII. Pressure Switches, LOW-PRESSURE Switch

OPERATING	5 MIN
TIME

T1

_

T2

BLK DENOTES CLOSED CONTACTS

HN67ZA002

A91436

3	OPERATING	5 MIN
SEC	TIME
T1
_
T2
BLK DENOTES CLOSED CONTACTS
HN67PA025, HN67ZA003, HN67ZA008

A91437

Fig. 16—Cycle-Protector Sequence

CUT YELLOW WIRE

BETWEEN CONTACTOR AND

LOW-PRESSURE SWITCH

Y		YEL	SAFETY	YEL
			CONTROL
	TERMINAL			YEL
	BOARD
	CONNECTION

YEL	C	BRN	C
VIO		TERMINAL
		BOARD
		CONNECTION

T1 LOGIC T3

BLK

T2

A88415

Fig. 17—Cycle-Protector Wiring

DSV

CH

11 21

A91426

Fig. 18—Wiring for Single-Pole Contactor

thereby improving the efficiency of the system. The sequence of operation is that on closure of the wall thermostat and at the end of a fixed on-delay of 1 sec, the fan relay is energized. When the thermostat is satisfied, an off-delay is initiated. When the fixed delay of 90 ± 20 sec is completed, the fan relay is de-energized and fan motor stops. If the wall thermostat closes during this delay, the

—17—

TDR is reset, and the fan relay remains energized. The TDR is a 24v device that operates within a range of 15 to 30v and draws about 0.5 amps.

If the blower runs continuously instead of cycling off when the fan switch is set on AUTO, the TDR is probably defective and must be replaced.

VII. PRESSURE SWITCHES

Pressure switches are protective devices wired into control circuit (low voltage). They shut off compressor if abnormally high or low pressures are present in the refrigeration circuit. Depending on unit model, you may find a low- and/or high-pressure switch in system.

LOW-PRESSURE SWITCH

Located on suction line of condensing unit only, the low-pressure switch protects against low-suction pressures caused by such events as loss of charge, low airflow across indoor coil, dirty filters, etc. It opens on a pressure drop at about 27 psi. If system pressure is above this, switch should be closed. To check switch, turn off all power to unit, disconnect leads on switch, and apply ohmmeter leads across switch. You should have continuity on a good switch. Because these switches are attached to refrigeration system under pressure, it is not advisable to remove this device for troubleshooting unless you are reasonably certain that a problem exists. If switch must be removed, remove and recover all system charge so that pressure gages read 0 psi.