Contactors - A.O. Smith dre-52 Service Handbook

CONTACTORS

This section of the manual provides information on how contactors used on Electronic
Control Models are constructed, how they work and how to test contactor operation - see
Figure 2 on page 9 for location of the contactors on these models. Surface Mount Control
Models are not equipped with contactors.
Contactor Construction - How They Work
Magnetic contactors are used on Electronic Control Models to energize and de-energize the
heating elements. Power from the fuse blocks is supplied to the heating elements through
three switches (3 poles) inside the contactor. Springs located inside the contactor hold the
switch contacts open; the springs are compressed and the spring tension forces or holds the
switch contacts in their normally open state.
The contactor's switches are closed by an electromagnetic coil inside the base of the
contactor. When a call for heat is activated the electronic control system sends 120 volts to
the contactor's electromagnetic coil. As current runs through the coil it becomes
"magnetized" and overcomes the spring tension holding the switch contacts open. The
switch contacts then close which in turn sends power to the heating elements. When the call
for heat is satisfied the control system de-energizes the contactor coil and spring tension
returns the contacts to their open position.
3 Pole Contactor Side View
OPERATION & SERVICE
Heating Element
Power Circuit
Wiring Terminals
Electromagnetic
Contactor Coil Wiring
Terminals 120 VAC
3 Pole Contactor Side View - Cover Plate Removed
Servicing should only be performed by a Qualified Service Agent
3 Pole Contactor Internal Wiring
T3 T2
L3 L2
29
T1
3 Normally
Open Switch
Contacts
L1
Electromagnetic
Contactor Coil
Contactor Springs
Hold Contacts Open
When Electromagnetic
Coil Is Not Energized