Bryant R-22 service manual Pressure Switches, Low-PressureSwitch AC Only, Personal Injury Hazard

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. Puron pressure switches are specifically designed to operate with Puronr systems. R-22 pressure switches must not be used as replacements for the Puronr air conditioner or heat pump. Puronr pressure switches are identified by a pink stripe down each wire.

Low-Pressure Switch (AC Only)

The low-pressure switch is located on suction line and 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 50 psig for Puron and about 27 for R22. If system pressure is above this, switch should be closed. To check switch:

1.Turn off all power to unit.

2.Disconnect leads on switch.

3.Apply ohmmeter leads across switch. You should have continuity on a good switch.

NOTE: 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. Never open system without breaking vacuum with dry nitrogen.

!CAUTION

PERSONAL INJURY HAZARD

Failure to follow this caution may result in personal injury.

Wear safety glasses, protective clothing, and gloves when handling refrigerant.

To replace switch:

1. Apply heat with torch to solder joint and remove switch.

!CAUTION

PERSONAL INJURY HAZARD

Failure to follow this caution may result in personal injury.

Wear safety glasses when using torch. Have quenching cloth available. Oil vapor in line may ignite when switch is removed.

2.Braze in 1/4-in. flare fitting and screw on replacement pressure switch.

High-Pressure Switch (AC & HP)

The high-pressure switch is located in liquid line and protects against excessive condenser coil pressure. It opens around 610 or 670 psig for Puron and 400 psig for R22 (+/- 10 for both). Switches close at 298 (+/- 20) psig for R-22 and 420 or 470 (+/-

25)psig for Puron. High pressure may be caused by a dirty condenser coil, failed fan motor, or condenser air re-circulation. To check switch:

1.Turn off all power to unit.

2.Disconnect leads on switch.

3.Apply ohmmeter leads across switch. You should have continuity on a good switch.

NOTE: 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 gauges read 0 psi. Never open system without breaking vacuum with dry nitrogen.

!CAUTION

PERSONAL INJURY HAZARD

Failure to follow this caution may result in personal injury.

Wear safety glasses, protective clothing, and gloves when handling refrigerant.

To replace switch:

1. Apply heat with torch to solder joint and remove switch.

!CAUTION

PERSONAL INJURY HAZARD

Failure to follow this caution may result in personal injury.

Wear safety glasses when using torch. Have quenching cloth available. Oil vapor in line may ignite when switch is removed.

2.Braze in 1/4-in. flare fitting and replace pressure switch.

Loss of Charge Switch (HP Only)

Located on liquid line of heat pump only, the liquid line pressure switch functions similar to conventional low-pressure switch.

Because heat pumps experience very low suction pressures during normal system operation, a conventional low-pressure switch cannot be installed on suction line. This switch is installed in liquid line instead and acts as loss-of-charge protector. The liquid-line is the low side of the system in heating mode. It operates identically to low-pressure switch except it opens at 23 (+/- 5) psig for Puron and 7 (+/- 5) psig for R22 and closes at 55 (+/- 5) psig for Puron and 22 (+/- 5) for R22 Two-stage heat pumps have the low-pressure switch located on the suction line. The two-stage control board has the capability to ignore low-pressure switch trips during transitional (defrost) operation to avoid nuisance trips. Troubleshooting and removing this switch is identical to procedures used on other switches. Observe same safety precautions.

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