SERVICING
30 Rev 1
S-22 REVERSING VALVE REPLACEMENT
WARNING
Disconnect Electrical Power Supply:
Capture the refrigerant charge from the system.
When brazing a reversing valve into the system, it is of
extreme importance that the temperature of the valve does
not exceed 250°F. at any time.
Wrap the reversing valve with a large rag saturated with
water. "Rewet" the rag and thoroughly cool the valve after
each brazing operation of the four joints involved. The wet
rag around the reversing valve will eliminate conduction of
heat to the valve body when brazing the line connection.
The use of a wet rag sometimes can be a nuisance. There
are commercial grades of heat absorbing paste that may be
substituted.
After the valve has been installed, leak test, evacuate and
recharge.
S-23 DEFROST TIMER BOARD
The Defrost Timer Board is an electronic device which is not
field repairable. If a malfunction should occur the complete
board must be replaced.
DEFROST CYCLE
The defrosting of the outdoor coil is jointly controlled by the
defrost timer board, defrost (30/60) control, and compressor
run time.
Solid State Timer RHA-A2A Models
The defrost timer board can be connected for one of three
(3) time intervals. Post T
1
= 30 minutes, Post T
2
= 60
minutes, and Post T
3
= 90 minutes (Factory connected).
The timing interval can not commence until the outdoor coil
temperature reaches approximately 30°F. (initiation tem-
perature) at the defrost terminator (30/60) control point of
contact. As long as this point of contact does not reach 60°F.
(termination temperature), the defrost timer board will count
the number of minutes that the compressor runs.
At the end of this (one of three) time interval, the defrost
timer board will call for defrost and energize the defrost
(DFR) relay. This relay has four sets of contacts of which one
is in the line voltage circuit (normally closed) in series with
the outdoor fan motor. When this contact opens, the
outdoor fan motor stops. The other three sets of contacts
(normally open) are in the low voltage circuit. One set of
contacts control the reversing valve. When closed, the
reversing valve energizes, switching over to the cooling
position sending hot refrigerant gas to the outdoor coil,
which will start to melt any frost accumulation. Another set
of contacts close, locking in the compressor until defrost is
completed. The third set will energize the electric heat if
available.
The defrost timer board will keep the defrost (DFR) relay
energized until the outdoor coil temperature reaches ap-
proximately 60°F at the 30/60 control, or a maximum of 10
minutes compressor run time.
If the defrost cycle is terminated by temperature, then a new
time interval count cannot begin until the defrost (30/60)
control again reaches approximately 30°F. If the defrost
cycle was terminated by time, then a new time interval would
begin immediately.
The following has been simplified in order to illustrate the
Electronic functions:
TIME TEMPERATURE DEFROST CONTROL
(RHA-A mdls)
COM
TST
HLD
24VAC
OUT
T1
T2
T3
1. When the defrost (30/60) control closes (coil tempera-
ture at approximately 30°F.), the solid state board be-
comes programmed.
2. Whenever the (CC) compressor contactor is energized,
the solid state timer counts the compressor run time. If
(CC) cycles those accumulated minutes are retained as
long as the Defrost (30/60) control stays closed.
With the wire connected to T
3
terminal, the count time is
for 90 minutes (factory wired). Terminal T
2
= 60 minutes,
terminal T
1
= 30 minutes (field changeable) - Timer count
time may be accelerated for testing only, by shorting TST
Terminals. (Example: 90 minutes = approximately 21
seconds).
3. At end of the programmed time, common circuit (C) is
made to the (OUT) terminal. The defrost (DFR) relay
becomes energized and will stay energized until defrost
(30/60) control opens by coil temperature, or after 10
minutes of run time. Maximum defrost time limited to 10
minutes compressor run time.
