Troubleshooting - Johnson Controls T500HCP-1 User Manual

T
roubleshooting
Table 8: Troubleshooting
Symptom
No display/faint display ...
Keyboard inoperative ...
Thermostat will not call for
heat ...
Thermostat will not call for
cooling ...
Fan does not turn on ...
AC appears on the LCD ...
LCD shows missing or
extra segments ...
Possible Cause
Supply voltage incorrect
System transformer weak or
overloaded
Thermostat damaged
because system voltage
was greater than 30 VAC
Keyboard locked
Compressor delay still in
progress
Thermostat setpoint is
satisfied
Compressor delay still in
progress
Thermostat setpoint is
satisfied
Fan failure
20-30 VAC is absent from
24V and 24V(c)
LCD failure
T500 Series Programmable Thermostats Product/Technical Bulletin
Corrective Action
Use a voltmeter to check the voltage between the 24V and
24V(c) terminals. Voltage should be between 20-30 VAC.
If voltage is less than 20 VAC, disconnect the thermostat
and check the voltage between 24V and the other system
wires; see possible causes below. If voltage is greater than
30 VAC, troubleshoot the power source and replace the
thermostat.
Check and/or replace with a suitable 24V transformer.
Replace with new thermostat and ensure new thermostat is
isolated from the system using suitable relays and a
transformer of the proper rating.
Switch the keyboard DIP switch to the unlocked position.
Wait - equipment short cycle protection in progress.
Raise the heating setpoint using the
Wait - equipment short cycle protection in progress.
Lower the cooling setpoint using the
Place a jumper between terminals R and G. Fan should
come on. If it does not, troubleshoot the fan system. If fan
does come on, replace the thermostat.
Using a voltmeter, measure voltage between the 24V and
24V(c) terminals. If the reading is less than 20 VAC, check
system transformer. If the voltage is between 20-30 VAC,
replace the thermostat.
Replace the unit.
∧ ∧ ∧ ∧
button.
∨ ∨ ∨ ∨
button.
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