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Clicking contactor on air handler

I have had two different HVAC companies and several techs look at my system to try to troubleshoot my problem, they all had different answers. And I'm tired of hanging parts trying fix the problem. I have  Trane Heat Pump with an American Standard air handler. I have went through three contactors on the furnace (air handler) in the last couple of years. They start clicking at five to ten second intervals, usually early in the morning, them start buzzing until the contacts are burned up. Parts that I have replaced already as per their suggestions are defrost timer board on heat pump, both sequencers on heat banks, and thermal sensor. Cleaned blower housing, and replace filter every two weeks.  Checked charge on heat pump. Replaced thermostat with digital one. Still no help. I am not a professional, but can figure out most problems, but this one is driving me nuts. I am not a rich man, and can't afford these guys charging $ 100.00 per trip to suggest more parts. Any ideas would be greatly appreciated. 


  • Wayne_16
    Wayne_16 Member Posts: 130
    edited December 2010
    Has the supply voltage to the contactor been measured while clicking?

    Measure the supply voltage to the contacter coil.  If the voltage is erratic or less than 20-21 volts the coil will be energized then de-energized  then energized again. 

    May need to use a analog meter to see the voltage fluctuation.  Digital meters do some averaging to show a value on the scale.  (Sorry I know others know exactly what is happening internally in the meter).  The point is the digital meter may not show the voltage drop if a relay or electronic control board are controlling this relay. 

    If the voltage is erratic, then it is a matter of locating the culprit and making repairs., wiring transformer, supply voltage to the furnace, thermostat wires, thermostat, limit controls, etc.  Could be a bad ground someplace.

    Here is a excellent case of following the current path to locate the fault, rather than hop-scotch testing.  Place one meter lead at the transformer neutral.  Start at the transformer 24 volt terminal with the second lead, test each wire/component in the order of the circuit to identify the fault.  Do not overlook anything or assume something is okay.  This is a time where a temporary jumper with alligator clips comes in handy.  The jumper can be used to verify a suspected wire/component.  Remove the jumper after testing.  Do not leave any jumpers across limit controls.

    Thanks, Minnesota Wayne
  • Techman
    Techman Member Posts: 2,144

    contactors are not good . 1st ,is to check the low voltage at the contactor coil upon start-up.It should be 22-27 vac. If it is lower ,say 18-21vac,then check some of the following.What is line voltage  reading on the load side[ towards the compressor } of the contactor upon start-up.If line volts reading drops ,so does the low volts.If line volts stay normal ,then check the low volt xformer to see if it is wired properly. You need to know the hi volts in the house and match the hi volt connections of the xformer to the house volts. A house w/ a 208 vac supply and a xformer wired to the 230-240 vac tap will cause this type of complaint.
  • Coany
    Coany Member Posts: 91
    edited December 2010
    some things to try

     what exactly is drooping in/out in response to the clicking?

     does the relay drop in/out in emergency heat position, try it and see

    is the fan dropping in/out with the clicking, try using the fan "on" position.

    put  only one screw in the cover so WHEN ITS happening you can open it quickly and listen closely to which relay is clicking in/out

    once you decide exactly which relay is dropping in/out

    look hard at the wiring diagram on the door

    decide what that relay is controlling

    decide where the control signal for that relay comes from.

     to me; what your describing sounds like a control signal problem

     semi-shorted wire or poor connection somewhere in the 24v circuit.

     then follow the advice given above
    " Do what you can, with what you have, where you are" Teddy Roosevelt
  • geno54
    geno54 Member Posts: 43
    Some things to consider

    Some not so obvious things to consider for chattering contactors

    Poor solder connections on control board

    Loose screw terminal connections

    Poor splice connections

    Pinched wires Possibly when stapled

    Wires laying on hot water or hot gas pipes and grounding out

    Wires chaffing on metal

    Plus all the advice above, on finding the voltage drop
  • DanCanDo
    DanCanDo Member Posts: 15
    Check Thermostat

    I've been finding my fair share of "chattering" controls as a result of "Power Robbing" Thermostats...if it's electronic and doesn't require a Common or batteries, beware.  Jump it out and see if the chattering stops.
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