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Basic ElectricalBasic Electrical

ContactorsContactors

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• A contactor is used to control an electric load in a control system.

• Contactors make or break a set of contacts that controls the voltage applied to some load in HVAC systems.

• A contactor consists of a coil that opens and closes a set of contacts due to the magnetic attraction created by the coil when it is energized.

• A contactor is used to control an electric load in a control system.

• Contactors make or break a set of contacts that controls the voltage applied to some load in HVAC systems.

• A contactor consists of a coil that opens and closes a set of contacts due to the magnetic attraction created by the coil when it is energized.

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Parts of a contactorParts of a contactor

Coil

Contacts

Control Voltage Terminals

Line Voltage Terminals

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ApplicationsApplications

• The largest electric load in any cooling system that requires control is the compressor.

• The contactor used in a small residential air conditioning unit probably controls the compressor and condenser fan motor.

• Larger Air conditioning systems will have multiple contactors.

• The largest electric load in any cooling system that requires control is the compressor.

• The contactor used in a small residential air conditioning unit probably controls the compressor and condenser fan motor.

• Larger Air conditioning systems will have multiple contactors.

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Simple schematic diagram of a contactor controlling a compressor and Condenser fan motor

Simple schematic diagram of a contactor controlling a compressor and Condenser fan motor

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OperationOperation

• Different manufacturers design contactors in different ways. But they serve the same purpose: Opening and closing a set of contacts.

• The armature of a contactor is the portion that moves.

• This can be accomplished by two ways:» A sliding armature» A swinging armature

• Different manufacturers design contactors in different ways. But they serve the same purpose: Opening and closing a set of contacts.

• The armature of a contactor is the portion that moves.

• This can be accomplished by two ways:» A sliding armature» A swinging armature

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Contactor with a sliding armatureContactor with a sliding armature

Armature

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• The sliding armature is mounted between two slots in the frame of the contactor and moves up and down in these slots.

• The sliding armature is mounted between two slots in the frame of the contactor and moves up and down in these slots.

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Contactor with a swinging armatureContactor with a swinging armature

Armature

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• The swinging armature is mounted on a pivot or hinge and moves up and down in a swinging motion.

• The swinging armature is mounted on a pivot or hinge and moves up and down in a swinging motion.

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• The armature of a contactor is connected by a mechanical linkage to a set of contacts that causes a complete circuit when the armature is pulled into the magnetic field produced by the coil.

• This operation applies for both the swinging armature and sliding armature.

• The armature of a contactor is connected by a mechanical linkage to a set of contacts that causes a complete circuit when the armature is pulled into the magnetic field produced by the coil.

• This operation applies for both the swinging armature and sliding armature.

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• The magnetic field that closes a contactor is created by a coil wound around a laminated iron core.

• The magnetic field that closes a contactor is created by a coil wound around a laminated iron core.

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• When the coil is energized, a magnetic field is created around the laminated core.

• The core then becomes a electromagnet of sufficient strength to attract the armature closing the contacts.

• Some contactors have a spring mounted between the armature and the stationary contacts to ensure the contactor opens when the coil is de-energized.

• When the coil is energized, a magnetic field is created around the laminated core.

• The core then becomes a electromagnet of sufficient strength to attract the armature closing the contacts.

• Some contactors have a spring mounted between the armature and the stationary contacts to ensure the contactor opens when the coil is de-energized.

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CoilsCoils

• Coil characteristics depend on the type of wire and the manner in which it is wound.

• Coils are designed to be operated on 24, 120, 208/230 and occasionally 480 volts.

• To identify the coil voltage, the voltage is marked on it.

• Coil characteristics depend on the type of wire and the manner in which it is wound.

• Coils are designed to be operated on 24, 120, 208/230 and occasionally 480 volts.

• To identify the coil voltage, the voltage is marked on it.

Coil voltage is marked here!

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ContactsContacts

• The contacts of a contactor make a complete circuit when the contactor is energized, allowing voltage to flow to the controlled load.

• Contactor are rated by the ampere draw they can carry.

• There are two types of loads a contactor can control:

» Inductive loads ( Motors)» Resistive loads ( Heaters)

• The contacts of a contactor make a complete circuit when the contactor is energized, allowing voltage to flow to the controlled load.

• Contactor are rated by the ampere draw they can carry.

• There are two types of loads a contactor can control:

» Inductive loads ( Motors)» Resistive loads ( Heaters)

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• Contacts are made of silver and cadmium, which resists sticking.

• The chemical composition of contacts can operate at cool temperatures up to 125% of their current –carrying capacity.

• Contactors are usually manufactured with two or three poles.

• Contacts are made of silver and cadmium, which resists sticking.

• The chemical composition of contacts can operate at cool temperatures up to 125% of their current –carrying capacity.

• Contactors are usually manufactured with two or three poles.

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• Two pole contactor is required for single phase systems.

• A three pole contactor is required for three phase systems.

• Two pole contactor is required for single phase systems.

• A three pole contactor is required for three phase systems.

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TroubleshootingTroubleshooting

• To diagnose a faulty contactor requires looking at three sections of the contactor:

– The coil– The contacts– And the mechanical linkage

• A defect in any part of these parts can cause the contactor to fail.

• To diagnose a faulty contactor requires looking at three sections of the contactor:

– The coil– The contacts– And the mechanical linkage

• A defect in any part of these parts can cause the contactor to fail.

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The coilThe coil

• The coil must be in good condition to create a strong enough electromagnetic force to pull in the contacts.

• It’s uncommon for the coil to become so weak that it does not close the contacts, unless there is excessive friction to the mechanical linkage.

• A coil is diagnosed as either good, open or shorted.

• The coil must be in good condition to create a strong enough electromagnetic force to pull in the contacts.

• It’s uncommon for the coil to become so weak that it does not close the contacts, unless there is excessive friction to the mechanical linkage.

• A coil is diagnosed as either good, open or shorted.

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• The coil can be checked with an ohmmeter. • If the coil is shorted, resistance will read 0• If the coil is opened, resistance will read OL• If the coil is good, the resistance will read some

measurable resistance.

• A coil can also be checked by applying voltage to it and observing the contactor to see if it closes.

• The coil can be checked with an ohmmeter. • If the coil is shorted, resistance will read 0• If the coil is opened, resistance will read OL• If the coil is good, the resistance will read some

measurable resistance.

• A coil can also be checked by applying voltage to it and observing the contactor to see if it closes.

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• A voltage reading of the coil should be taken before checking the coil to see if the contacts should be closed.

• If voltage is applied to it, the coil will cause a direct short and other damage could result…. So BE CAREFUL!

• A voltage reading of the coil should be taken before checking the coil to see if the contacts should be closed.

• If voltage is applied to it, the coil will cause a direct short and other damage could result…. So BE CAREFUL!

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ContactsContacts

• The contacts must be in good condition to ensure that the proper voltage reaches the load.

• A visual inspection is sufficient to diagnose bad contacts.

• A voltage reading taken across the contacts of the same pole will show the voltage drop across the contacts.

• The contacts must be in good condition to ensure that the proper voltage reaches the load.

• A visual inspection is sufficient to diagnose bad contacts.

• A voltage reading taken across the contacts of the same pole will show the voltage drop across the contacts.

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Contact conditionsContact conditions

Pitted and burnt contacts

Good Contacts

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• Any voltage drop above 5% of the rated voltage is considered to be excessive.

• If you come across this, replace the contactor.

• Voltage must be applied to make this check.

• Any voltage drop above 5% of the rated voltage is considered to be excessive.

• If you come across this, replace the contactor.

• Voltage must be applied to make this check.

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Mechanical linkageMechanical linkage

• The easiest fault to diagnose.• Any problem with the mechanical linkage

can be detected by visual inspection.• The mechanical linkage will usually fail do to

wear, corrosion, or moisture

• The easiest fault to diagnose.• Any problem with the mechanical linkage

can be detected by visual inspection.• The mechanical linkage will usually fail do to

wear, corrosion, or moisture

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Repairing contactorsRepairing contactors

• Contactors can be repaired by using replacement parts.

• Some manufacturers do sell a kit that will completely replace the contact portion of the contactor.

• Parts can be difficult to locate, it might be better to just replace the contactor.

• Contactors can be repaired by using replacement parts.

• Some manufacturers do sell a kit that will completely replace the contact portion of the contactor.

• Parts can be difficult to locate, it might be better to just replace the contactor.

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