Central A/C Will Not Start


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Old 05-02-11, 06:30 AM
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Central A/C Will Not Start

My fairly new central A/C system is not starting. Replaced the system about 6 years ago and it worked fine every season. Had a few warm nights last week and decided to placate my kids. Set the thermostat to cool, indication showed the system was on but nothing. The compressor does not go on and no blower. Looked at the circuit breaker panel and all was good. The panel was replaced when we updated the A/C system so this is new as well. Any idea where I should start looking?

I see there's what appears to be a separate power cut-off outside by the compressor, this is also new. Tried pulling the handle but did not want to force it.
 
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Old 05-02-11, 11:57 AM
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Good start would be thermostat batteries and then check for blown low voltage fuse inside furnace or air handler on the control board.
 
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Old 05-02-11, 02:48 PM
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set the stat to fan "on" and see if it comes on. could be a low voltage short or blown fuse. something is wrong in your low voltage circuit
 
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Old 05-03-11, 05:03 AM
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Replaced the batteries and still nothing.

Set to cool / fan on and still nothing.

Where would I find the fuse / circuit board? The compressor is outside, everything else is in the attic. We only have ducting for the upper level of our split. The A/C is a separate system from the baseboard heat.
 
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Old 05-03-11, 01:48 PM
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the stat could be bad, but i highly doubt it. you may have a blown transformer. if you have a meter, see if you have 24v on the secondary side of the transformer which should be inside the air handler. if you have 24v next thing would be check the circuit board. make sure you also have power to your air handler. if power was out to your air handler you will not get a 24v signal even if the xformer is good.
 
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Old 05-04-11, 09:51 AM
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Opened the air handler (Unitary Products Group Cooling Models F2RC / F2FC 024 Thru 036) and found the circuit board. The fuse ('5' amp(?)) is definitely blown. I'll replace it and see if this is the only problem.

I noticed on the condenser(?) there is a fair amount of rust where all the tubes connect. Should I expect this on such a fairly new unit? I'll take some pictures when I am up there again replacing the fuse.
 
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Old 05-04-11, 10:37 AM
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The fuse blew for a reason, and you need to determine where the short is in the low voltage circuit.

Rust is expected with just about any age system. Due to steel and water forming rust byway of oxidation.
 
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Old 05-05-11, 02:29 PM
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Replaced the fuse and everything is working fine for now. Took some pictures of the system and posted on Facebook. One shows the rust I am concerned about.

My A/C will not start | Facebook
 
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Old 05-05-11, 05:23 PM
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the rust is normal in that location. Check for chewed wires outside by the a/c unit. or inside the electrical panel of the a/c. Be prepared for mouse/chipmunk nest in electrical compartment. Fuse blew for a reason..... best to find it now rather than wait till it happens again and it is 130F in your attic.
 

Last edited by hvactechfw; 05-05-11 at 05:48 PM.
 

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