# no 24volts to air conditioner contactor



## darnold (Apr 29, 2012)

American Standard Freedom 80 Circuit Board.
Does the circuit board control the 24 volts to the contactor on the air conditioner?


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## carmon (May 8, 2010)

24 volts leaves the furnace on R and goes to stat..returns to furnace on Y and Y and C send 24 vac out to condensing unit... unless you have a heat pump...


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## darnold (Apr 29, 2012)

When activating the stat for furnace fan (blower works). When fan placed on auto and turn on the a/c, the furnace fan works, but nothing is happening with the air conditioner and no 24 volts to the a/c. Have 24 volts intermittently to a/c.


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## carmon (May 8, 2010)

you could check on the furnace for 24 volts on Y and C ... if you have steady 24 volts there... problem between furnace and condensing unit... is there 24 volts in the junction box in the condensing unit.... may be a low ambient time delay relay ,open pressure switch... check the two wires at condensing unit right where they go in...


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## darnold (Apr 29, 2012)

No voltage on Y and C in furnace circuit board.


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## carmon (May 8, 2010)

do the same test R to Y


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## darnold (Apr 29, 2012)

no voltage R to Y.


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## carmon (May 8, 2010)

you have power to furnace on I assume ie furnace door switch... you need 24 volts Y to C at furnace assuming there are wires on Y as it may just be a terminal... y from the stat may join wires to condensing unit with out being on the board you could also to speed things up join R Y and G at stat and see what happens


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## plummen (Jan 10, 2010)

carmon said:


> do the same test R to Y


R and Y shouldnt show power between them,check from Y to C on the board in furnace. 
If you have nothing between Y and C when stat is set to cooling check wiring between furace and stat or stat itself.
If all else fails remove the low voltage wires at the condensor and where they leave the furnace area,twist them together on 1 end and ohm the 2 wires on other end to check continuity.
The low voltage wires outside are often casualties of dogs,lawn mowers/weed wackers.


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## carmon (May 8, 2010)

plummen said:


> R and Y shouldnt show power between them,check from Y to C on the board in furnace.


I asked that all ready he had none y to c so i asked to check r to y to see if stat was no good or broken wire...:whistling2:


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## darnold (Apr 29, 2012)

Thank you for your time and information, Carmon. I must stop at this time, I will try the three wire connection.


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## plummen (Jan 10, 2010)

carmon said:


> I asked that all ready he had none y to c so i asked to check r to y to see if stat was no good or broken wire...:whistling2:


Got it.


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## Doc Holliday (Mar 12, 2011)

Is your system equipped with a float safety switch, wired into the condenser line? Check your drain pan for a switch and main drain line, in case you have an in line switch. 

just a short expanation; if a drain clogs and the condensate water gathers and collects then the switch, which is usually tied into the condenser line to shut said condenser off so no more condensate water can be produced, will trip. You will have fan on only while on call for cool but not the outside unit.


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## carmon (May 8, 2010)

that is a good thought.....


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## carmon (May 8, 2010)

plummen said:


> There was no need to ask him to do it in the first place,in order to show voltage you need a path back to neutral or ground.:whistling2:


well then i am sorry..... if I read 24 volts from r to y at furnace it tells me something.... thats what I was getting at...:whistling2::whistling2::whistling2::whistling2::whistling2::whistling2:


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## darnold (Apr 29, 2012)

Is a transformer located on the circuit board? In other words, does the circuit board have a way to reduce 120 volts to 24 volts for the outside unit?


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## Doc Holliday (Mar 12, 2011)

No, the external step down transformer does it.


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## carmon (May 8, 2010)

all the current splits i work on the 24 volts comes from funrace transformer..... i have seen hi voltage contactor coils but not for a while in my area....


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