Hvac guys.....central air issue

[Livesintrees]

So central air has run fine the past two weeks. Last night, nothing. Getting a hum and dimming lights every couple minutes. Being an electrician I’m thinking could be a capacitor in the unit. Fan on the unit outside works fine. Filters on the unit look fine. Air is being drawn up into the system but no cold air coming from the vents. Bought the house this past winter so this is the first time since home inspection the ac has been used. Any thoughts on what’s going on?

 

[ksgobbler]

Freon leak allowed all the refrigerant to escape?

 

[ACCMan]

Some of the capacitors are dual voltage. One side of the cap feeds the fan motor and the other side feeds the compressor. Look at cap and see if the case looks distorted, as this is a sure sign of a bad cap. Is the compressor running as you mentioned a humming and lights flickering? Look at the start relay as I have seen spiders and ants get in the relay blocking one side of the 220v causing a single phase condition to the compressor, hence humming when trying to start. If this happens the overload will take out the compressor until it cools, then compressor will try and start again. If the cap is ok, and relay is ok, and the compressor windings read continuity with an ohmmeter, but the compressor will not start I would put a hard start kit on the compressor. This is a secondary capacitor which gives the compressor an additional boost to start. I would try cutting off the thermostat, and killing the breaker to the unit for about a minute. Then turn on the breaker, then turn on the thermostat, set to cool and see what it does. I have seen control boards get a glitch and resetting power would correct the problem, especially after a storm when you get a surge from lightning. If this doesn't fix the issue check as I discussed above. Worst case is bad compressor, or out of gas and low gas safety has it taken out.

 

[wiscwhip]

Something similar to what AACMan posted happened to my FIL last summer, he only had 110v power going to the unit, so it would still "run", but not make cool air. Might be a good place to start.

 

[Turkey Creek]

Blower unit throw a bearing in the main trunk? Happened to me before.

 

[Buckly]

How old is the unit? Some newer units would shut off completely if they were low on refrigerant. Bad time of the year for the AC to break down. The dimming does sound like low voltage somewhere.

 

[ACCMan]

Do you have a package unit (everything outside on a concrete pad) or a split unit, part outside and an air handler/evaporator inside?

 

[Livesintrees]

Got it goin. Did a lot of continuity testing. Got a bad wire. Capacitor is corroded so I’ll be changing that out but the wire was bad halfway between the attic and the unit up on the side of the house. Took hours to find it but it’s up an running again for now. Thank god bc it was 98 here today.

 

[ACCMan]

Keep a spare cap and relay on hand cause they usually go out on a weekend when all businesses are closed.

 

[kskid]

Keep a spare cap and relay on hand cause they usually go out on a weekend when all businesses are closed.

X2

 

[Livesintrees]

Made a few changes yesterday. Ac guy I know came and gave the whole system a check. Rehung the unit in the attic. New pan. Shortened the pvc overflow runs. Then I installed and overflow shutoff switch in the pan. Installed an oversized mushroom style ran on the roof. Cools the attic faster even when not running bc of location. Removed the inadequate gable fan which was useless. Went outside opened and thoroughly cleaned the unit. Replaced capacitor. Being an electrician I rewired all connections that were accessible and replaced all crimp on ends. And finally I removed thermostat and installed a smart unit made by Ecobee. I highly highly highly recommend it to anyone thinking about it. It can be run off The touchscreen, or from a smart phone. Extra sensors can be added etc etc for hot or cold rooms which in addition to adjusting at the unit can really dial the house in to optimal. Best part is the stat was right at $130 which is leaps and bounds less then the popular nest brand. Only thing left is remove the filter that’s on the unit in the attic, cap it off and install filter at the return grill. I’m having a hinge grill made with a trim ring for better looks and sealing and ease of filter replacement.

 

[Bill]

My mess wasn't so easy. Two split systems up and down. Upstairs blew at the condensor outside, 0 freon.

That led the downstairs, which was low on freon, to work overtime and turn to a block of ice at the air handler in the basement.

Good news is both are still under warrenty....

Good thread though, I will have spare caps on hand now.