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I'm at a 10 ton trane roof top unit.I'm getting power to the contactor and the thermastat is calling for cooling but the compressor or fan motor is not coming on.There are two boards that I'm not familiar with.How can I check to see if one of the boards is fried?

Posted by rjwaters27 on

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mark92230

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It may be a little difficult to answer this without more info but I am going to try. You must mean you have high voltage power on L1 L2 and L3. This unit will not start if 1 out of 3 fuses is blown, so first make sure all fuses are good by taking them out and checking with an ohm meter.

If all fuses are good, the easiest things to check are the low and high pressure switches which may be manual reset. The low and High pres switch will be connected to the low side (big) tubing and the other to the high side (smaller tubing) A reset may be right on top of the switch.

* some low press switches will only close by pressure. If the unit is low on refrigerant, the low pressure switch will be open. You can wire around the low pressure switch if need to.

Also check for low voltage from thermostat. You should be getting 24 volts at C and Y on the terminal board where the thermostat wires come in to the unit from the thermostat. If not, try jumpering R, Y and G together to see if unit will come on.

Lastly, on some circ. boards will be small blade type fuses usually 3 or 5 amp. If these fuses are blown the unit will not come on.

I hope some or any of this helps you. If I had a picture of the electrical components I could probably help you more.

Posted on Jun 16, 2011

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Check the capacitor(s) to see if they are working ok, then move to the wiring and see if there are any that are burned or loose ect. Then move on to the boards and do a visual check for buns ect. What is the model of this RTU and are there any other symptoms? Is this a heat pump? Does it have an economizer section? We need more in depth information before we can help you diagnose this unit.

Posted on Jun 16, 2011

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