• Outdoor HVAC unit contacts are burned

    Apr.7.2011

    Both sets of contacts, main contact 40 a. and defrost board contacts, are burned. Is it possible that the intake fan is stuck? 3.5 ton, six years old.

    The outdoor unit has a contactor that energizes and de-energizes the compressor. These contacts become burned and pitted over time during normal operation. If they become so bad that they partially melt and stick together, then the compressor will stay energized and continue to run even when there is no call from the thermostat for the air conditioning system to run. This will cause freeze-ups and compressor damage, since the indoor fan will not be running at the proper speed, if at all. Additionally, if the system is a heat pump, the outdoor fan will not run all the time the compressor is running, which can cause additional problems. This is due to the fact that the fan is controlled by another relay located on the defrost board. Very rarely this relay could overheat and stick closed which would keep the outdoor fan running continuously. A worn contactor is one item checked during an AC tune-up visit and can be replaced before it results in a system failure and resulting damage to the compressor. Please contact a professional HVAC contractor, like ARS/Rescue Rooter. We also offer Home Service Plans which help keep your HVAC system in top shape all year with two comprehensive seasonal tune-ups, one in the spring and one in the fall. 

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