York Rooftop Unit: B3CH

Re: DEFROST SEQUENCE OF OPERATION

The BCH has a unique “ambient modified” time-temperature defrost control that automatically adjusts to changes in the outdoor temperature.

The defrost control will shorten the defrost initiation time periods above 35°F and will extend the defrost initiation time periods below 35°F.

The control is factory set to defrost at 110 minutes (T3), but it can be field adjusted to defrost at 80 minutes (T2) or 50 minutes (T1) in areas with high humidity.

EXAMPLE: If the time is factory set on pin T-3 (110 minutes at 35°F outdoor) and the outdoor temperature climbs to 45°F, the time initiation cycle decreases to 100 minutes.

If the outdoor temperature drops to 10°F where ice is less likely to form, the 110 minute interval increases to 150 minutes.

Two requirements must be met before a defrost cycle can be initiated.

• The defrost time cycle must be complete.
• The liquid line temperature must be less than 28°F.

Defrost terminates when the liquid line sensor reaches 55°F or after 10 minutes.

The defrost time cycle restarts 10 minutes after the start of the defrost cycle even though the liquid sensor terminated defrost after 3 minutes.

► During troubleshooting, the defrost time can be reduced to 20 seconds by shorting out the SW1 test pegs on the module.