HVAC Procedure and Performance Guide

TASK: Install heat-pump defrost timer

Training for this procedure can be found in these courses:

                         131 – Oil Heat l  and  161 – Boilers l


Defrost timer must be installed according to manufacturer’s specifications.  Timer must be securely mounted, connections must be mechanically secure and electrical continuity must be established.  Defrost timer must control defrost cycle according to specifications.  Applicable safety procedures must be followed.


    1. Review job order and manufacturer’s specifications.
    2. Determine voltage, current and cycle requirements for equipment, type of timer required, number of normally open and normally closed contacts required, cycle requirements, voltage requirements and contact rating.
    3. Collect tools, equipment and materials.
    4. Put on safety and protective equipment and apparel.
    5. Disconnect electrical power to equipment.
    6. Remove old timer.
    7. Verify that new timer is a suitable replacement according to specifications.
    8. Mount new timer and connect wiring according to specifications.
    9. Reconnect power and verify that voltage is correct and that timer operates correctly.
    10. Set desired cycle times.
    11. Place equipment in operation, monitor defrost cycle and adjust timer as required.
    12. If equipment does not operate to specifications, troubleshoot and make required adjustments and repairs.
    13. Leave system in required operating status.
    14. Remove safety and protective equipment and apparel.
    15. Gather tools, equipment and leftover materials and leave work site clean.
    16. Do follow-up check after equipment has operated through several cycles and make adjustments as necessary.