Check Defrost Air Switch (DAS)
refrigeration
Description
The defrost air switch called for defrost within eight minutes of termination for two consecutive cycles; alarm only, and the defrost air switch will not initiate defrost.
Activation Conditions
The defrost air switch has called for a defrost cycle within eight minutes of a defrost termination for two consecutive defrost cycles. (The air switch contacts were closed continuously for 15 seconds before the defrost cycle was started.)
Unit Behavior
Alarm only. While this alarm is active, the defrost air switch will NOT be used to initiate a defrost cycle; however the Defrost Timer will initiate a defrost cycle 90 minutes after the alarm comes on and the manual defrost switch will remain operative.
Reset Conditions
Auto reset when defrost cycle terminates correctly, and the air switch does not call for a defrost cycle within the eight minutes following defrost termination, or alarm may be manually reset using the display mounted keys or by turning the unit off, then back on again.
Corrective Actions
1. Check Condition of Refrigerated Compartment and Load a. Check condition of refrigerated compartment doors and seals. Doors must be closed and door seals must seal and prevent entrance of outside air. b. Check condition of evaporator. Check for blockage sufficient to cause an air pressure differential across the coil great enough to close the contacts of the defrost air switch. Coil must be free of ice following defrost. c. Check condition of product. If product is warm and moist, frequent defrost cycles can be expected. 2. Check DAS Power and Wiring a. Inspect switch, connector pins and terminals. Verify that there is no physical damage to switch or damage or corrosion in connections. b. If required, power switch by placing the unit in PC mode. Check for power at switch connector. Must have minimum 0.5 VDC. If not, check connectors and wiring between terminals for damage, moisture or corrosion. c. Check for continuity from switch connector plus terminal to 1-2MSM-17. If good continuity is not present, check connectors and wiring between terminals for damage, moisture or corrosion. d. Check for continuity from switch connector minus terminal to 1-2MSM-26. If good continuity is not present, check connectors and wiring between terminals for damage, moisture or corrosion. 3. Check Defrost Air Switch and Tubing: Check tubing and perform testing as required. Refer to Section 8.9.10.2.