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trane conderser unit not starting

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this unit will start if i push the contactor manually

so i know the comp and cond fan and cap are ok

i checked the thermostat wire and i do have continuety

thru the wire i cant seem to measure 24 volts to the unit

this may be due to using a 15 year old analog meter im useing

on 2nd thought it wouldnt cause jumped the contactor

wires to the tstat still nothing my question is theres a

transfomer in the blower unit im guessing thats stepping the 110 to 24 volts to send to the cond unit the also a

main control board on the blower unit in the apt

which i think is my problem but not sure how to check it

as a side note i have 2 units side by side neither

started this year im trying to get this one going first

its gooing to the top floor which is pretty hot

this is a trane m/n for cond unit is ttro42c1ooa1

s/n is h22273646 the air handler m/n is tud12oc96a01

the main control board in the air handler #is 50a50-405

which i think subs to cnt03797 sorry for the long post but wanted to get the nessary info in any help appreciated

i think im going to buy the board and transformer this unit does it sound like im on the right track?

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Need appliance parts? Call 877-803-7957 now!

Jedi Appliance Guy

   Don't buy anything till you've checked it.  I would suspect a faulty wire nut connection before I would just order a board.  Is the evaporator fan running?  How is the filter? Can you see the coil? Is it dirty? It is best to start at the air handler and work your way to the condenser and then see if charged and draining correctly.  One of the low voltage wires going to your contactor should go to Y on your thermostat.(or main board)  The other should go to low voltage common in your air handler.  Probably marked B. Are you working on the right condenser? (it could happen).  Try going on a 5 story roof with 60 condenser units up there.  If both condensers aren't running you can put your ear up to each one and listen for the pulled in contactor.  

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thanks for the reply yes the filter is clean the blower is running the charge im not positive but i know its not out

on low presure or anything your right about the tstat connections only difference my tstat wires are brown and white my main question is will the control board keep the condensing from starting if so can i jump it out also do uknow if the transformer in the blower unit is to send 24 volts to the cond unit im not geting low voltage to the contactor from the blower unit im an appliance tech myself

so im determinded to fix this myself and learn more about central air systems thanks for the help

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Guest ahammer48


Whoa, Slow down there buck-a-roo. In order to become a good trouble shooter U have to start with the simple stuff 1st

Do U have main power to both the furnace and condenser sections. If yes then carefully remove the thermostat from its subbase to expose the wires. On the subbase U will C  terminals marked "R, Y, W,G". Set UR meter to A/C volts and put 1 probe on R and the other on G. Do U have 24 VAC? Check R to the other terminals. U should have 24 VAC between R and the others.

If U have it read on. If not then most likely the step down transformer in the furnace section has burnt out. Watch thou. Some times the transformers are protected by a fuse and it could just B the fuse thats bad. Be carefull. Always folllow caution when dealing with electricity.

If U have24 VAC at the stat do this. Put the stat back on. Turn main power off to the condenser section and take off the panels to expose the contactor, capacitor, etc. You will C 2 wires going to the coil of the compressor contactor. Not !!! the main power wires. The 2 wires U want are the smaller ones. Take one of the wires off the contactor and make sure it dosen't touch anything.

Go inside and make UR thermostat call for cooling. Make sure the fan starts. Now go back to the condenser. With UR meter still set to VAC and main power still off, put one probe on the wire still connected to the contactor and touch the other probe to the wire U took off. Have 24VAC?? If yes then the contactor is bad and thats why the condenser section isn't running.

If no then U could have a defective stat or a break in the wires going out to the condenser, or as Jedi said, are we sure were looking at the right machine, since U have 2 side by side.

Hope this helps:)

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the problem was a bad wire connection on the thermostat

respliced and connected problem solved

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