Time-Delay Relay (Tdr); Pressure Switches - Bryant Base Series Application Manual And Service Manual

Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual

Time-Delay Relay (TDR)

The TDR is a solid-state control, recycle delay timer which keeps indoor
blower operating for 90 sec after thermostat is satisfied. This delay
enables blower to remove residual cooling in coil after compression
shutdown, thereby improving efficiency of system. The sequence of
operation is that on closure of wall thermostat and at end of a fixed on
delay of 1 sec, fan relay is energized. When thermostat is satisfied, an off
delay is initiated. When fixed delay of 90 ± 20 sec is completed, fan
relay is de-energized and fan motor stops. If wall thermostat closes
during this delay, TDR is reset and fan relay remains energized. TDR is a
24v device that operates within a range of 15v to 30v and draws about
0.5 amps. If the blower runs continuously instead of cycling off when
the fan switch is set to AUTO, the TDR is probably defective and must
be replaced.

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 Puron systems. R-22 pressure
switches must not be used as replacements for the Puron air conditioner
or heat pump. Puron 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 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 screw on replacement pressure
switch.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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.
!
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.
!
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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CAUTION
CAUTION