hvac tech here with a strange situation

Old 07-29-11, 07:57 PM
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hvac tech here with a strange situation

let me know if anyone has ever come across this. new luxaire unit at a vet today. call was no cooling. went up to the third floor and heard crackling. right away I knew the coil was frosting up, but no fan. stat was calling for cooling and had 24v at the Y terminal of the circuit board inside the handler as well as 24v at the G terminal but no fan. weird huh? it gets better. I turn the fan to "on", fan comes right on. I tested the heating system, furnace came on, moments later fan comes on. as soon as i put the cooling back on, condenser came on but no fan again. took the green wire off the terminal block to make sure i wasnt reading feedback and i had 24v on the line. removed the two wires going to condenser and turned the cooling on and nothing happened. the schematic shows that the Y terminal goes into a cooling circuit but it doesnt show the cooling circuit. I'm gonna do some research and find out what controls the fan when cooling is called for. havent worked on a luxaire yet and this threw me for a whirl. i left the fan "on" just to circulate air but told them i had to order a new board since thats the only thing i can think that it would be.
Old 07-30-11, 12:34 PM
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if you get the fan in the ON position on the stat and go for auto/FAN cool and get nothing thats the board...if you didn't get FAN/ON from the stat go right to the motor in the future....and especially that you cycled the fan thru the heating call...the onlt thing you might want to check if the stat is digital with a deep menu the FAN in cooling calll might have a timed config.or delay or something you'll find out when the board goes in

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