The equipment in this month’s article is a two-stage air conditioning system. The operating conditions are high ambient, and the customer’s complaint is that there is no cooling. Upon your arrival and performing an initial survey of the situation, you determine that the indoor air handler is operating, that the control system is properly set for the cooling mode, and the temperature in the building is 90 degrees.

When you check the outdoor section of the equipment, you find that the outdoor fan motor, which is an ECM type that operates on a PWM (Pulse Width Modulation) control system, is trying to start, but not operating. After determining that there is no blade obstruction, you perform two voltage tests at the points shown in Figure One and get the following results: 

  1. At the L1 and L2 connections, your meter shows 230 VAC.
  2. At the PWM connections your meters shows a DC voltage measurement within the manufacturer’s specifications for high stage operation of the equipment.

As your next step, you disconnect the equipment power supply and confirm that all the terminal connections in the control lead wiring harness are OK.

Your troubleshooting question: What is the next step you need to take in servicing this equipment?

Compare your answer with ours HERE.

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