and start the system, if the compressor has been off 5
minutes. With fan switch in “AUTO” position, a circuit is
made from thermostat heating contact through blower relay
to provide blower operation.
4. The system will cycle in response to thermostat signal to
provide heating as needed.
5. Supplemental electric heaters are energized by second
stage of heating thermostat.
TEST PINS
The test pins labeled “speed-up” and “defrost” are provided to
aid in field servicing of the E*FB heat pump. See Figure 10.
The pins are designed to be temporarily shorted together either
by a screwdriver or with a 1/4" female spade connector.
When the “speed-up” pins are shorted together, ALL timings
are speeded up by a factor of 64. This reduces the anti-recycle
compressor timer from 5 minutes to about 5 seconds and the
defrost terminate time from 14 minutes to 13 seconds: addi-
tionally, the 39 minute minimum run time would be shorteded
to about 40 seconds or less if the system has operated for some
period of time since last defrost.
When the “defrost” pins are shorted together, the control will
allow the unit to go into a defrost cycle if the compressor is
operating. When the short is removed, the heat pump will
remain in defrost until the coil temperature reaches 75
°
or 14
minutes expires.
If the liquid (coil) temperature happens to be above 75
°
F, the
short must be maintained to keep the unit in a defrost cycle. It
should be noted that caution should be used since the unit WILL
REMAIN in defrost unitl the short is removed regardless of coil
temperature. This could cause a lockout due to high discharge
pressure!
NOTE: Anytime the “defrost” shorting pins are jumpered, it
automatically resets all timing cycles. After a power
failure, all timing cycles would also reset except one
that is the 5 minute delay for compressor restart. It can
be reduced, however, by jumpering the “speed-up”
pins on the control board.
DEFROST CYCLE
Frost and ice which forms on the outdoor coil during the heating
cycle must be defrosted when it blocks the air flow through the
coil.
Due to the arrangement of the refrigerant circuit within the
outdoor coil of these units, frost may accumulate unevenly in
different sections of the coil. However, a normal defrost may
occur even though the coil is not completely covered with frost.
Three requirements must be met before a defrost cycle can be
initiated.
1. A minimum of 39 minutes must have elapsed since last
defrost.
2. The liquid line temperature must be less than 40
°
F.
3. The coil temperature must be below the defrost initiation
temperature for 4.5 minutes continuously.
NOTE: Under certain low ambient conditions normal trigger-
ing of a defrost cycle could be prevented. Therefore as
a precautionary measure a “Forced Defrost” is initiated
every six hours to insure compressor longevity by return-
ing oil back to the sump.
Defrost will terminate when the coil temperature reaches 75
°
F
or after 14 minutes defrost time.
LOCK-OUT CONTROL
If the discharge pressure reaches 400 PSIG, during either the
heating or cooling mode, a lock-out will occur. A lock-out will
turn on the emergency heat light on the thermostat.
Turning the thermostat switch to “off” then back to “on” will reset
the system.
OPERATION IN EMERGENCY HEAT POSITION
When switch on thermostat is placed in emergency heat posi-
tion:
1. Emergency light is energized.
2. Compressor circuit is locked out.
3. Supplemental and standby heaters (if installed) will be
controlled by first stage of heating thermostat.
FIGURE 10- DEFROST TEST PINS
SPEED-UP
TEST PINS
DEFROST
TEST
PINS
515.26-N1Y
Central Environmental Systems
11
