Compressor and Condensor Fan not coming on


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Old 04-28-19, 12:04 PM
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Compressor and Condensor Fan not coming on

I have the misfortune of owning a Trane.

Last summer I replaced the $500 condensor fan motor along with a $10 capacitor.

This summmer I realized even though the inside blower was moving air, the outside condensor was doing nothing.

There is 120 + 120 to the contact switch. Off the contact switch side terminals, there’s 27v and 11 ohms between them. Everything south of the contactor has 27v in and out: Time delay, ballast looking thing and little square epoxy filled doohickey.

Wires going to the “new” fan motor have 27v and two wires have 120v each + ground wire.

If I depress the contactor plunger, the compressor kicks on but the fan doesn’t. There’s also 120v to the capacitor at this time, but nothing comes out the other side.


Thoughts?
 
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Old 04-28-19, 01:53 PM
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You need to check for 240vAC across the contactor....... not 120v + 120v which doesn't tell you anything.
You need to check for 24vAC across the contactor coil.....not from the terminals to ground.

The 240vAC source will have no affect on the 24vAC. So if you don't have the 24v at the coil..... check where the thermostat wiring connects to the condenser. Directly at the wire nutted connections. If you have power there you may be low on refrigerant.
 
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Old 05-04-19, 08:52 AM
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Okay, so I replaced the contactor switch $9 and capacitor $3. Cheap parts swap, same issue.

I have 240v across 120v line connection.
I have 0v across coil, though each line does have 24v when testing to ground.

Theres only 3 wires from the “thermostat” that connect to anything at the condensor. When testing to ground, the yellow and brown have 24v. The blue, which goes to the low pressure switch? has nothing. This blue wire connects to the B/C wire at the unit inside and has no power there either. It does not go to the thermostat.
 

Last edited by Number4; 05-04-19 at 10:03 AM.
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Old 05-04-19, 03:06 PM
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Check for 24VAC where the cable from the house comes into the outside unit. Typically, the cable connects to the internal wiring of the outside unit using wire nuts. If you have 24VAC at the wire nuts when the thermostat is calling for cooling, everything from the house to the outside unit is good. The low pressure switch should be wired in series between the 24VAC from the Y terminal in the house and one of the coil contacts on the contactor. If the refrigerant gets too low so that the pressure is low, the switch opens, preventing the contactor from turning on and possibly damaging the compressor.
 
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Old 05-04-19, 11:12 PM
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Just a helpful hint..... especially to others. Don'r replace a contactor unless you know it's bad.
If you wire it wrong.... it's twice as hard to repair the unit.

B/C is the Trane common connection...... or typically ground.... BUT not always. That's why I don't recommend checking from the wiring to ground. I don't know why your condenser has three wires. It uses the blue/C connection and one other for the contactor. So you need to check from yellow to blue and brown to blue. Typically it's the yellow and blue wires.
 
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Old 05-18-19, 08:46 AM
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So, system had no refrigerant in it. Over winter (presumably some last season) it leaked out about 13 lbs worth of R410a.
 
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Old 05-18-19, 10:45 AM
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I'm sorry to hear that. Quite a disappointment.
 
 

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