Just replaced old condenser (unit kept drawing too much power and tripping breaker, continuously getting worse) with Lennox AC13 and matching line set and evaporator coil.

New AC unit cooling house and breaker does not trip, but one problem still exists with the new unit that we had with the old unit - sometimes the AC gets into a pattern where the condenser and fan are on for 20-60 seconds, the condenser and fan turn off then the fan immediately turns on again for 20-60 seconds (purge cycle), then they both come on again and the cycle repeats. This pattern can last for more than 30 minutes.

The house has 3 zones, each with a thermostat. This pattern usually happens when one zone is close to or at the set temperature, but the AC is still commanded to run (based on the snowflake symbol on the thermostat). The other zones are usually not active when the pattern occurs.

Any ideas of what may be wrong? Thanks in advance.

If you have a low pressure control in the outdoor unit it may be kicking off on this switch , this can happen due to low on refrigerant . Lack of air flow will cause the system to run at a lower pressure. Need to watch it with a set of guages on the system to varify.

It is a low ambient out door temp switch. The fan will not com on until the head pressure in the condenser hits a certain level and then turns the fan off when the pressure is too low etc. when it cycles on and off again, block condenser airflow with cardboard and see if the fan stays on continuously. Only do this when the outdoor temp is below 70 degrees or you have gauges on to monitor the head pressure.

it is a low ambient out door temp switch. the fan will not com on until the head pressure in the condenser hits a certain level and then turns the fan off when the pressure is too low etc. when it cycles on and off again, block condenser airflow with cardboard and see if the fan stays on continuously. only do this when the outdoor temp is below 70 degrees or you have gauges on to monitor the head pressure.

Look for a green module with two blue wires coming out of it on the smaller liquid line. This is the low ambient kit installed to let customers run ac when it is too cool outside.