SERVICING
33
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 (208/240 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).
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 CONTROL
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 control capillary senses the pressure in the
compressor discharge line. If abnormally high condensing pres-
sures develop, the contacts of the control open, breaking the con-
trol circuit before the compressor motor overloads. This control
is automatically 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 condenser 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 LOW PRESSURE SENSOR
The low pressure sensor senses the pressure in the suction line.
Follow the following sequence to check the low pressure sensor
in the suction line.
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
1. Disconnect power to the air conditioner.
2. Disconnect the sensor from the electric board.
3. Connect an ohmmeter across the sensor terminals. The
ohmmeter should be the resistance shown in the following
table. Replace the sensor if the sensor is open, shorted
or outside the valid resistance range.
-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
tected Pr
es
su
re
(
P
SI
G)
Output Voltage (DCV)
RESISTANCE AND PRESSURE CHARACTERISTICS
