Watlow QPAC Modular SCR Power Control Service - Manual (Page 24)

24 WATLOW QPAC Service Manual
Troubleshooting, Chapter 5
Q33
Problem: No Heat
Blown Fuse
This can be done one of two ways. Measure voltage across the fuse. If there is
voltage present the fuse is bad. You can also check the fuse for continuity using an
ohmmeter. Replace the fuse if necessary.
Open Heater
Check all the connections from the circuit breaker to the heaters. Measure the
heater current. Next, measure the voltage across the heater. If voltage is present
and no current is flowing, there is a bad connection or heater. Disconnect the
heater from the power control. Check the resistance of each element. The resis-
tance should correspond with the heater KW rating. If not, replace the heater.
Bad Connection
Check all the connections from the circuit breaker to the heaters. Measure the cur-
rent and output voltage from the heater. If voltage is present and no current is flow-
ing, there is a bad connection or heater. Repair or replace.
Open Limit or Safety Contactor Within the Thermal System
The overtemperature limit contactor may have tripped. Check the limit or safety
contactor. Locate the cause for the limit tripping, correct and reset.
Command Signal Polarity is Backwards
Verify that the 4-20mA control signal from the temperature control is wired correct-
ly. Make sure Terminal 5 is (-) and Terminal 4 is (+) on the control card.
The SCR Switch Will Not Turn ON
With the command signal full ON, check the VAC voltage across the L1 and T1 ter-
minals. They should read approximately 1.5VAC. If you are reading the line volt-
age potential, the SCR is not gating on. The mother board or control card may be
bad. Try another control card or contact the factory.
The Interlock Connection on the QPAC Control Card is Open
Measure voltage from Terminal 5 (-) to Terminal 1 or 2 on the control card. Voltage
must be present at both Terminal 1 and 2. If not, place a jumper between these
terminals. If you are using the interlock feature, check the interrupt switch or the
interlock.
The Unit is in Emergency Shut Down (ESD) - For Fan-Cooled Units ONLY
If the heat sink temperature exceeded 187°F (86°C) the on-board thermostat will
close and the QPAC will enter Emergency Shut Down. More than likely a clogged
or non-operational fan is the cause. Check the fan and clean if necessary. If the
problem still exists, check for a shorted heat sink thermostat. Measure from the
thermostat, unclog the fan, check for fan power, or replace the fan.
The Control Card is Bad
First, try to re-seat the control card. Make sure there is a good connection between
the control card and the mother board. If there is still a problem, replace the control
card with another card. Also, check the troubleshooting section on Page 29 or 30.
See Page 5 for ordering a replacement card.