SERVICING
42
S-4
CHECKING TRANSFORMER AND CONTROL CIRCUIT
HIGH VOLTAGE !
D
ISCONNECT
ALL
POWER
BEFORE
SERVICING
OR
INSTALLING
. M
ULTIPLE
POWER
SOURCES
MAY
BE
PRESENT
. F
AILURE
TO
DO
SO
MAY
CAUSE
PROPERTY
DAMAGE
,
PERSONAL
INJURY
OR
DEATH
.
WARNING
A step-down transformer (208/230 volt primary to 24 volt second-
ary) is provided with each indoor unit. This allows ample capac-
ity for use with resistance heaters. The outdoor sections do not
contain a transformer (see note below). (see indoor unit WIRING
DIAGRAM)
D
ISCONNECT
ALL
POWER
BEFORE
SERVICING
.
WARNING
1. Remove control panel cover, or etc., to gain access to trans-
former.
With power ON:
L
INE
V
OLTAGE
NOW
PRESENT
.
WARNING
2. Using a voltmeter, check voltage across secondary voltage
side of transformer (R to C).
3. No voltage indicates faulty transformer, bad wiring, or bad
splices.
4. Check transformer primary voltage at incoming line voltage
connections and/or splices.
5 If line voltage available at primary voltage side of transformer
and wiring and splices good, transformer is inoperative. Re-
place.
S-12 CHECKING HIGH PRESSURE SWITCH
HIGH VOLTAGE !
D
ISCONNECT
ALL
POWER
BEFORE
SERVICING
OR
INSTALLING
. M
ULTIPLE
POWER
SOURCES
MAY
BE
PRESENT
. F
AILURE
TO
DO
SO
MAY
CAUSE
PROPERTY
DAMAGE
,
PERSONAL
INJURY
OR
DEATH
.
WARNING
The high pressure switch senses the pressure in the compressor
discharge line. If abnormally high condensing pressures develop,
the contacts of the control open, breaking the control circuit be-
fore the compressor motor overloads. This control is automati-
cally reset.
1. Using an ohmmeter, check across terminals of high pressure
control, with wire removed. If not continuous, the contacts
are open.
2. Attach a gauge to the dill valve port on the base valve.
With power ON:
L
INE
V
OLTAGE
NOW
PRESENT
.
WARNING
3. Start the system in charge mode and place a piece of card-
board in front of the outdoor coil, raising the condensing
pressure.
4. Check pressure at which the high pressure control cuts-out.
If it cuts-out at 605 PSIG to -17 PSIG, it is operating normally
(See causes for high head pressure in Service Problem Analy-
sis Guide). If it cuts out below this pressure range, replace
the control.
S-13 CHECKING OUTDOOR HI/LOW PRESSURE SENSOR
The HI/LOW pressure sensor senses the suction pressure in cool-
ing mode, and the discharge pressure i heating mode. Folloe the
following sequence to check the pressure sensor. Connect a volt-
meter across the sensor terminals between the black and white
wirings. The voltmeter should show the voltage in the following
table. Replace the sensor if the sensor is open, shorted or outside
the valid voltage range.
L
INE
V
OLTAGE
NOW
PRESENT
.
WARNING
-200
-100
0
100
200
300
400
500
600
700
800
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
De
te
ct
ed
Pr
essu
re
(
P
SI
G
)
Output Voltage (DCV)
VOLTAGE AND PRESSURE CHARACTERISTICS
