How do you diagnose a bad contactor?

To test the contactor, you’ll need a multimeter (available at any hardware or big box store). Set it to the “OL” setting. Connect the multimeter to the low volt terminals on both sides of the contactor. If the contactor is working properly, the multimeter will show a reading between 5 and 20.

What causes a contactor to not engage?

AC contactor not pulling in is not a major issue. Usually, the contactor malfunctions due to corroded contacts, coil failure, and contactor burnout. 1. Corroded Contacts – The contact points in an AC contactor are susceptible to corrosion because of moisture present in the air.

How many ohms should a contactor have?

The meter should read from 10 to 100 ohms. If the meter does not, the coil is bad and must be replaced.

When should a contactor be replaced?

Your contactor can fail electrically in one of three ways. The coil can become shorted, grounded, or open. Your technician will use a meter to determine the resistance crossing your contactor. If the readings are outside of a very narrow range; your contactor should be replaced.

How many ohms Should a coil read?

You should have a resistance reading of at least 3-4.5 ohms. A bad coil will show a higher reading then 3-4.5. Next, place the red or black lead from the meter to the centre of the coil , and to either one of the terminals positive or negative. You want 9500-10000 Ohms, a little less is ok but no more.

Why is my contactor chattering?

Contactor chatter can also occur due to chattering switches or loose connections in the control circuit. A low voltage situation can also occur due an unbalanced loading of the motor. The higher resistance will cause a voltage lag which in turn could lead to contactor chattering.

Do contactors wear out?

In most cases, the contactor does not simply wear out from normal use. Usually, the reason for contactor failure is misapplication. That’s why you need to understand the basics of contactors. When someone uses a lighting contactor in a motor application, that’s a misapplication.

How do you test for bad contacts on a contactor?

Place the red lead to the L1 and the black lead to T1. The meter should read 0 ohms. Perform the test on each separate set of contacts. Keep each set test together–L1 to T1, L2 to T2 and L3 to T3. Each set should read 0 ohms. If any set does not, then that contact is bad. The contacts may have to be replaced.

How do you identify wires on a contactor?

Identify the wires, if needed, with the clear tape and pen. Place identifier marks such as L1, L2 and L3 with the pen over the tape. Adhere the tape to the corresponding wires. Loosen and remove the wires from the T or terminal side of the contactor. Identify each wire as in Step 1, but with a T1, T2 and T3.

How do you test for a direct short in a circuit?

The meter short read 0 ohms or a direct short. Test each set of L1-to-T1 contacts. Place the red lead to the L1 and the black lead to T1. The meter should read 0 ohms. Perform the test on each separate set of contacts. Keep each set test together–L1 to T1, L2 to T2 and L3 to T3. Each set should read 0 ohms.

How do you test a coil with a voltage meter?

Touch each lead of the meter to each connector on the coil. The meter should read the supplied voltage. Read the specification for the circuit to find the voltage supplied. If the voltage is correct and the coil still does not close, shut all power off to the coil.