Troubleshooting Flowcharts - Lennox HP21 Unit Information

VIII−TROUBLESHOOTING FLOWCHARTS
The following flowcharts show how to diagnose problems
in two-speed heat pumps equipped with TSC control.
Table 19 shows how to determine if the TSC is functioning.
Tables 20a and 20b show how to correlate TSC diagnostics
to the unit.
Follow the flowcharts step by step. Disconnect as few
TROUBLESHOOTING FLOWCHART
CHECK VOLTAGE ACROSS COMPRES-
SOR CONTACTOR COILS. IS THERE 24
VAC ACROSS HIGH-SPEED CONTACTOR
COIL?
THREE-
PHASE
NO
YES
HIGH−SPEED OR
LOW-SPEED
CONTACTOR IS
FAULTY.
TURN OFF UNIT POWER AT DISCONNECT FOR AT
LEAST 3 SECONDS. TURN POWER ON AND ALLOW
3 SECONDS FOR CONTROL TO POWER-UP.
APPLY THERMOSTAT DEMAND.
CHECK UNIT VOLTAGE AND
MANUALLY RESET CONTROLS.
TRY TO START COMPRESSOR
BY PRESSING AND RELEASING
MANUAL OVERRIDE BUTTON.
DOES COMPRESSOR
TWO-SPEED CONTROL
UNIT WILL NOT RUN
IS DIAGNOSTIC LED
LIT?
NO
SINGLE-
PHASE
IS THERE 24 VAC
ACROSS LOW-
SPEED CONTACTOR
COIL?
IS THERE 24 VAC
ACROSS LOW-SPEED
CONTACTOR COIL?
YES NO
CONTROL MAY
LOCKED OUT. BREAK
AND REMAKE THERMO-
STAT DEMAND. DOES
COMPRESSOR START?
NO YES
CONTROL IS PROBABLY GOOD
AND THE PROBLEM IS LOCATED
ELSEWHERE IN THE UNIT. PRO-
CEED
SHOOTING FLOWCHART IN THE
UNIT INFORMATION MANUAL TO
START?
LOCATE THE PROBLEM. START
BY CHECKING ALL MANUALLY
RESET CONTROLS.
wires as possible. Any time a repair is made, reassemble
the unit and retest for operation. If the unit does not oper-
ate, recheck up to that point and then continue through the
chart. Occasionally more than one specific problem may
exist. Do as little disassembly as possible and double
check your diagnosis before replacing components.
Be sure to remove all jumper wires and replace all wire con-
nections and access panels before placing unit back in
service.
TABLE 19
NOTE−Before beginning this troubleshooting pro-
cedure make sure that 1) primary side of contactor
is supplied with line voltage 2)indoor and outdoor
transformers are delivering 24vac and 3)line volt-
age is supplied to compressor terminals when
contactors engage.
YES
YES
NO
IS THERE 24 VAC
ACROSS
SPEED CONTACTOR
COIL?
NO
NO
YES
HIGH-SPEED AUXILIARY
SWITCH IS NOT MAKING
PROPERLY. REPLACE
BE
CONTACTOR.
NORMAL LOCKOUT
CONTROL WAS LOCKED OUT DUE TO UNIT PROB-
LEMS. CONTINUE THROUGH TROUBLESHOOT-
ING FLOWCHART IN THE UNIT INFORMATION
MANUAL TO LOCATE REASON FOR LOCKOUT.
NO YES
THROUGH TROUBLE-
Page 50
CONTROL MAY BE LOCKED OUT. TURN
POWER OFF AT DISCONNECT FOR 3 SEC.
IS DIAGNOSTIC LED STILL LIT?
LOW-
YES
REPLACE
CONTROL
YES
HIGH−SPEED OR LOW-
SPEED CONTACTOR
IS FAULTY.
SAFETY DORMANT LOCKOUT
CONTROL IS NOW OUT OF SAFE-
TY DORMANT LOCKOUT AND HAS
RESUMED NORMAL OPERATION.
DO NOT REPLACE CONTROL..
SAFETY DORMANT
WAS PROBABLY CAUSED BY A
SELF-TEST FAILURE OR LINE
VOLTAGE SPIKE.
NO
LOCKOUT