36
IM620-1
3.
Remove power from the controller by opening CB1. Try to improve the connections in the
Aux/Out plug insulation displacement terminals by pressing down on the wires with a small
screwdriver.
4.
Check all other wiring and connectors for bent pins or miswires.
a.
If the chatter does not stop, the electromechanical relay or contactor is probably defective.
Troubleshooting Solid-State Relays
As shown on the unit wiring diagrams, the solid-state relays on the Output Boards all have normally
open “contacts.” Actually, these contacts do not exist as they do in an electromechanical relay.
Instead of using contacts to switch the load, the solid-state relay changes its resistance from low
(closed), when it is energized, to high (open), when it is de-energized. (This high resistance is
approximately 100K ohms.) Because the output circuit through the solid-state relay remains
continuous regardless of whether the relay is energized, troubleshooting a solid-state relay with a
voltmeter can be tricky.
In a typical circuit, a power source is connected across a single relay output and a load (see
Figure 20). In this circuit, a solid-state relay behaves like an electromechanical relay. If the relay is
energized, the relay output is hot. If the relay is de-energized, voltage cannot be measured at the relay
output.
The circuit shown in Figure 21 is similar to a typical circuit; the difference is that there is an open set
of contacts, or a disconnection between the relay output and the load. In this circuit, a solid-state
relay does not behave like an electromechanical relay. if the solid-state relay is energized, the relay
output is hot (as expected). However, if the solid-state relay is de-energized, the relay output still
appears to be hot. This is because the relay output and the voltmeter form a continuous circuit in
which the relay’s resistance, though high, is insignificant compared to the voltmeter’s resistance.
This means that nearly all the voltage is dropped across the voltmeter. Therefore, the voltmeter
indicates that voltage is present. If a low wattage light bulb of the appropriate voltage is used instead
of a voltmeter, the bulb’s low resistance loads the circuit enough to eliminate the false voltage
indication. In this situation, an incandescent test lamp is a better tool than a voltmeter.
Figure 20. Testing a Typical Relay Circuit
M10
0V
115 VAC
Output Board
DO 13
28
27
Neutral
