Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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Use following formula to calculate capacitance:
Capacitance (mfd)= (2650 X amps)/volts
3. Remove any capacitor that shows signs of bulging, dents, or
leaking. Do not apply power to a defective capacitor as it may
explode.
Sometimes under adverse conditions, a standard run capacitor in a
system is inadequate to start compressor. In these instances, a start assist
device is used to provide an extra starting boost to compressor motor.
This device is called a positive temperature coefficient (PTC) or start
thermistor. It is a resistor wired in parallel with the run capacitor. As
current flows through the PTC at start-up, it heats up. As PTC heats up,
its resistance increases greatly until it effectively lowers the current
through itself to an extremely low value. This, in effect, removes the
PTC from the circuit.
After system shutdown, resistor cools and resistance value returns to
normal until next time system starts. Thermistor device is adequate for
most conditions, however, in systems where off cycle is short, device
cannot fully cool and becomes less effective as a start device. It is an
easy device to troubleshoot. Shut off all power to system.
Check thermistor with ohmmeter as described below. Shut off all power
to unit. Remove PTC from unit. Wait at least 10 minutes for PTC to cool
to ambient temperature.
Measure resistance of PTC with ohmmeter.
The cold resistance (RT) of any PTC device should be approximately
100-180 percent of device ohm rating.
12.5-ohm PTC = 12.5-22.5 ohm resistance (beige color)
If PTC resistance is appreciably less than rating or more than 200
percent higher than rating, device is defective.
Cycle Protector
Bryant thermostats have anti-cycle protection built in to protect the
compressor. Should a non-Bryant stat be utilized, it is recommended to
add a cycle protector to the system. Solid-state cycle protector protects
unit compressor by preventing short cycling. After a system shutdown,
cycle protector provides for a 5 ± 2-minute delay before compressor
restarts. On normal start-up, a 5-minute delay occurs before thermostat
closes. After thermostat closes, cycle protector device provides a 3-sec
delay.
Cycle protector is simple to troubleshoot. Only a voltmeter capable of
reading 24v is needed. Device is in control circuit, therefore,
troubleshooting is safe with control power (24v) on and high-voltage
power off.
With high-voltage power off, attach voltmeter leads across T1 and T3,
and set thermostat so that Y terminal is energized. Make sure all
protective devices in series with Y terminal are closed. Voltmeter should
read 24v across T1 and T3. With 24v still applied, move voltmeter leads
to T2 and T3. After 5 ± 2 minutes, voltmeter should read 24v, indicating
control is functioning normally. If no time delay is encountered or device
never times out, change control.
Crankcase Heater
Crankcase heater is a device for keeping compressor oil warm. By
keeping oil warm, refrigerant does not migrate to and condense in
compressor shell when the compressor is off. This prevents flooded
starts which can damage compressor.
On units that have a single-pole contactor, the crankcase heater is wired
in parallel with contactor contacts and in series with compressor. (See
.) When contacts open, a circuit is completed from line side of
contactor, through crankcase heater, through run windings of
compressor, and to other side of line. When contacts are closed, there is
no circuit through crankcase heater because both leads are connected to
same side of line. This allows heater to operate when system is not
calling for cooling. The heater does not operate when system is calling
for cooling.
A97586
Fig. 6 – Wiring for Single-Pole Contactor
For 460V units, the CCH is controlled by a temperature switch and relay.
The relay is controlled by the temperature switch that is wired in series
with the low voltage indoor transformer connections, R & C, from the
low voltage harness assembly. If the OD ambient is above 85°F
(29.4°C), the CCH switch is open and the relay will be de-energized. In
this state, the CCH will not be energized. If the OD ambient goes below
65°F (18.3°C) and doesn’t rise above 85°F (29.4°C), the CCH switch is
closed and the relay will be energized. In this state, the CCH will be
energized when the compressor contactor is open. See
.
A170062
Fig. 7 – Wiring for 460 volt
The crankcase heater is powered by high-voltage power of unit. Use
extreme caution troubleshooting this device with power on. The easiest
method of troubleshooting is to apply voltmeter across crankcase heater
leads to see if heater has power. Do not touch heater. Carefully feel area
around crankcase heater. If warm, crankcase heater is probably
functioning. Do not rely on this method as absolute evidence heater is
functioning. If compressor has been running, the area will still be warm.
With power off and heater leads disconnected, check across leads with
ohmmeter. Do not look for a specific resistance reading. Check for
resistance or an open circuit. Change heater if an open circuit is detected.
WARNING
!
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or death.
Exercise extreme caution when taking readings while power is on.
