13-Troubleshooting Steps For No Cooling

Step-1: Always Start At The Thermostat

Index the system switch to "OFF", and the fan switch to "ON". That's it, that's Step-1.

Step-2: Is There Airflow From The Blower?

If there is airflow from the registers with the fan in the "ON" position, you at least know that the indoor unit has line voltage power, plus the low voltage transformer is also providing 24-volts to the controls. 

If there is no airflow, start by measuring the power supply to the indoor unit. If there is no power, check the switches, breakers, etc. If there is power, next test for power at the blower motor itself.

If there is no power at the blower motor, check to see of the fan relay coil is being energized with 24-volts. If the fan relay is not energized, check the 24-volt transformer output. If the fan relay is being energized, check the coil for continuity; replace if it measures "open".

If there is power at the blower motor, check the run capacitor. If the run capacitor is faulty (open, shorted, weak), replace it with a properly rated capacitor. If the run capacitor is fine, check the blower motor for continuity; replace if it measures "open".

If there is no 24-volts on the secondary side (R & C)of the transformer, check the line voltage on the primary side. If there is no line voltage, find the open libe voltage circuit. If there is line voltage, check the transformer for continuity on both the primary and secondary; replace if either side measures "open". 

If there is 24-volts on the secondary side of the transformer (R & C), install a jumper between R & G at the thermostat subbase. If the fan relay still doesn't get energized, you have an open wire, either unit to thermostat or inside the unit control panel/connections; ohm the wires separately and replace if any measure "open". If the fan relay does energize with the jumper in place, you have a defective thermostat; replace it.

Step-3: Reset The Thermostat

Index the system swith to "COOL", and the fan switch to "AUTO", and turn the setpoint down to 60-degrees.

Step-4: Is the Evaporator Airflow Clear?

If the airflow is clear, and appears to be blowing "strong", proceed to the outdoor unit at this time.

If the airflow seems "weak" or "not-so-strong", make a visual inspection of the airside components. Is the filter clean? Are all the RGDs open & clear? Is the motor speed correct? Is the evaporator coil clean? Is the secondary HX clean? Is the blower assembly clean? Are balancing dampers open? Are all zones open? Is there a bypass humidifer? Are there broken or crushed ducts? Is the motor rotation correct? 

If you answer "yes" to any of these potential issues, make the necessary corrections.

If you don't answer "yes" to any of these potential issues, perform a static pressure profile of the unit, recording all the pressure drops for analysis versus airflow standards.

Steps 5-13 Are Covered Separately.

 

 


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