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A421 Series Electronic Temperature Controls with Cycle Timer Product Bulletin

Product name
A421 Duty‐Cycle/Ventilation Models
Document type
Product Bulletin
Document number
Revision date

The fan relay is On for at least the Minimum Relay On-Time (Ont) during any Cycle Period (cP). See Figure 1.

The fan relay is Off when the sensed temperature is less than or equal to the OFF value.

If the temperature-based On-time (t1+t2) is less than Ont, only the remaining Ont [Ont minus (t1+t2)] is enforced at the end of the cP.

Figure 1. Cycle Timer behavior for free-cooling and ventilation control

The total On-time may exceed the Ont only when the sensed temperature On-time (t1+t2) is greater than Ont.

If the fan relay is On because for a time the sensed temperature is greater than or equal to Ont (earlier in the cP), then the fan relay remains OFF for the remainder of the cP.

The only condition that turns the fan relay On greater than the Ont is when the sensed temperature rises to the On value.