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HVAC will not function properly. Need help to diagnose.

I have an HVAC system installed in the house I live in. It hasn't functioned in the two years that I have lived here and would really like to lose the window units that I have now. I replaced the thermostat and wired it exactly as the previous thermostat was installed. The blower fan comes on when I switch the thermostat to cool, but the air never gets cold. The condenser fan outside never comes on and I never hear a compressor pump turn on either. All power breakers are flipped to on position and are not tripped. I have tested the coolant bleed valve and coolant sprays out. I have opened the outside panel on the condenser and found nothing to look damaged or burnt out. Due to lack of knowledge, that was the extent of the examination on the condenser and I replaced the access panel. Where should I look next?

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Well, I spent some more time this morning after doing some reading last night and I think I have narrowed it down to 1 of 3 options. I was able to get the compressor and fan to run when I found a test button on the contactor. It successfully started cooling the inside while I press the button in. I used a multimeter and tested all the connections and found that my 24v 40amp wires were not producing any power inside or out. So I disconnected power, used a wire brush and cleaning alcohol and polished all the terminals. I used sand paper to remove the corrosion on the copper wires and replaced them all one at a time to ensure they were properly hooked again. Still nothing from the 24v wire. So, my conclusion after what I read is I either have A) A bad transformer that needs to be replaced. B) A bad contactor that needs to be replaced. C) My refrigerant is lower that I think and a low coolant level switch has shut the circuit from running the machine.

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I guess my next question is, how do I test the transformer? Most likely I will leave it to a professional now that I know one of my friends husbands is a commercial HVAC certified tech. I would still like to know though if there is a way for me to check or if I need certain tools to continue forward with this endeavor.

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I would (after making sure power was off) try to turn the compressor and fan motors by hand to see if they are bound up and unable to run. If they are you can try to lube them and let it soak a day or two and try again to move them. If you can try running the unit--if you can't call a professional. If they turn normally you may have a bad starting capacitor which should be replaced by someone who understands electricity--you or a professional. Good luck. Ralph

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Nice Ralph. Be sure to use electrical motor lubricant/contact cleaner (usually 10 or 20 wt oil) and not something like WD-40 as it will mung up the contacts and possibly the motor windings/bearings or break down lubrication.

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Do you have 24 volts a/c to the contactor coil on a call for cooling? If you push in the contactor,( which is what test does) and it works then the question is why is the contactor not pulling in the when gets power )or if it gets power). You have 2 sides to a transformer, the primary which is line voltage in and the secondary which is, in this case, stepped down power out or your 24 volts out. Check the power out to t-stat on the R and common terminal of t-stat. Or check one of the contactor coil wires to ground. The coil is an electro-magnet so 24 volts makes it pull in the contactor and makes the connection across the contacts. I am willing to bet it is a low voltage issue. If it gets 24 volts then check continuty of coil.

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