# how to diagnose a bad heatstrip sequencer



## Final Notice (Aug 9, 2011)

i live in south texas so we dont get A TON of no heat service calls. but i would like to know, how do you properly diagnose a heating sequencer? and what do you check if both heating and cooling come on at the same time when there is a call for cooling?


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## beenthere (Oct 11, 2008)

See if it closes when 24 volts applied. then see if ti opens after 24 volts removed. keeping in mind it is a timed device, and you must allow time for it to close, and to open.


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## HVACDave (Oct 16, 2007)

If heat and cool both come on at the same time usually someone has tied into the fan leg without an isolation relay and is backfeeding on W when G is energized. Typical for A/C install on unit without terminal strip. (famous in older mobile homes in my area)


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## Final Notice (Aug 9, 2011)

beenthere said:


> See if it closes when 24 volts applied. then see if ti opens after 24 volts removed. keeping in mind it is a timed device, and you must allow time for it to close, and to open.


what causes the time delay within the sequencer? is it heat build up as current passes through it @ 24V?


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## JJboy (Oct 12, 2010)

Final Notice said:


> what causes the time delay within the sequencer? is it heat build up as current passes through it @ 24V?



The heat makes the thermocouple close like a on/off switch. So heat will continue building up until close the second stage and so on.


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## HVACDave (Oct 16, 2007)

When 24 volts is applied to the base terminals of the sequencer it energizes a heater in the bottom of the control. After a period of time (which varies depending on what time delay you purchase from the supplier eg. H 15-30 C 10-20 would mean when 24 volts is applied it will take between 15 and 30 seconds for the contacts of the switches above the heater section to close, which will turn on elements or fan,or energize another sequencer coil, then when the 24 volts is lost it will take 10 to 20 seconds for the contacts to re-open which will result in the elements, fan etc. to shut off.


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