Jim Johnson

In this troubleshooting situation, you are responding to a customer’s complaint of “not enough heat.” The equipment is an electric furnace that was installed in September 2013, and there is no service history up to this point. When you arrive, the customer explains the system worked fine last winter, and you confirm the discharge air temperature is significantly lower than normal. The volume of airflow is correct and the filter, replaced at the beginning of the season, is clean.

Your first step in evaluating the operation of the system is to make sure the thermostat is at a set point for several minutes, which would allow ample time for all four heating elements to be energized. After reviewing the equipment diagram (which you can view and download HERE), your ammeter check shows the proper current draw for the two elements connected by the red wiring to their sequencer. A check on the two elements connected by the yellow wiring to their sequencer shows a current draw of 0 A.

Proceeding to the next step in your troubleshooting procedure, you get the following results: 240 vac across connections M₁ and M₂ of the sequencer, 240 vac across connections M₃ and M₄ of the sequencer, and 24 vac at H₁ and H₂ of the sequencer.

Your two-part troubleshooting question:

1. What did your check of the M₁/M₂ and M₃/M₄ connections tell you about the condition of the elements, the limit switches, and fusible links wired in series with the elements?

2. What is the next step to take in servicing this equipment?

If you believe you have the answer to this troubleshooting problem, please submit your diagnosis by email to Jim Johnson at thenewstroubleshooting@techtrainassoc.com. In the subject line, please input: “Service Ticket Answer” and indicate which issue of The NEWS the problem you are responding to was published. You can also mail your answer to Technical Training Associates, P.O. Box 2259, Green Valley, AZ 85622-2259.

All correct answers will be entered into a drawing. The winner will receive a Fieldpiece LT-17A digital multimeter. The answer to this riddle, and the next HVACR Service Ticket column, is scheduled to appear in a June 2015 issue of The NEWS.

Publication date: 12/15/2014

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