Problem: Why I am not getting 24 volts to the contactor? Where does the 24 volts come from?
Answer: The 24 volts comes from a low voltage transformer. Please see the pictures of the two transformers below. The transformer has a primary (high voltage side) and a secondary (low voltage side). The high voltage side takes 110 to 240 volts AC and transforms the voltage to 24 to 28 volts AC. If the contactor is not getting the 24 volts to the contactor coil then it could be a time delay relay (if the unit is equipped), thermostat problem, transformer, safety control (low on refrigerate), or wiring problem. I would like to suggest that you turn the power off to the unit and check all your connections to make sure they are good and tight. You can turn the power back on and set the thermostat so the system is calling for cooling (AC ON). You could test the contactor with a voltmeter to see if you are getting 24 to 28 volts AC to the contactor 24-volt coil. If you are not getting any voltage to the contactor coil then this could be a blown fuse on your furnace or air handler control board. Please see the picture of the control with the fuse below. If the fuse on your control board is blown then you probably have a short in the thermostat wires or another control in the furnace or outdoor unit. We sell a universal time delay relay on the following page: Please click here if you would like to see the universal time delay relay we sell. We sell transformers on the following page: Please click here if you would like to see the Low Voltage Transformers we sell. Many air conditioners and heat pumps have low and high-pressure safety switches on them to protect the unit from damage if the system pressure is too low (low refrigerant charge) or too high (dirty outdoor unit, slow or bad condenser fan motor). If your unit is low on charge (I find most often) the safety switch will not allow the unit to start (contactor will not engage). You will need to call a service tech in order to check the charge on your unit. We sell contactors on the following page: Please click here if you would like to see the AC contactors that we sell. Please send us your unit’s model number if you would like for us to look it up and see which OEM contactor your unit requires. Our email address is: firstname.lastname@example.org Below we have a real good informative YouTube video made by grayfurnace man which shows how to troubleshoot and test a contactor. If you have any questions we will be glad to answer them. Please email us: email@example.com or comment in our comments section below. We would love to help you out and have your business!