All the AC contactors have been seen and measured, but how can they be distinguished on a machine? The engineers of electrical ac contactor manufacturers have summed up the following methods for reference.

First, see: A, see whether it works. B, if the contactor is absorbed after the start of the machine, the fan works, the press does not work (the capacitance is good), and the contactor can be judged to be bad. Because both the fan and the press are always controlled by the contactor, the contact work is synchronous. As one of the jobs, the other does not work roughly as the contactor bad

Second, listen: A, listen to whether there is a loud - squeak sound, such as it is (1) power supply voltage is low; (2) the contact point on the dirty material or core hybrid contact surface with dirty substances. If you hear a clicking and clicking sound, most of them are divided into two following cases: (1) low power supply voltage; (2) inadequate contact suction.

Third, smell: smell there is no coke burnt taste, if it please check the winding and contact.  

Fourth, measurement: first, disconnect the power, remove the line at the other end of the contact control, then beat it down with multimeter, then press the three main contacts of the test end and the other open contacts. They should all be switched on, and normally closed contacts should not be connected. Put down the end of the test, the main contact and the often open contact should not guide the normally closed contact. The coil value of the coil is about 200 batten. Before measuring, the line at one end should be removed and measured.  

Fifth, short circuit: boot, contactor, such as compressor does not turn, you do not know the contact of a contactor is bad, can be used to open the clamp, with two pointed short connection respectively of the same group on contact, so when the compressor work, that bad contact (Note: should Caution! In when you use this method)