Home AC help

[Dutchmanaz]

I've reached the end of my knowledge, a trail that certainly isn't all that long to be honest.
We had the AC systems semi-annual check up completed, and after which on the unit's contact switch switch had trouble holding closed and keeping it running. The tech said it happens (I agree but have trouble with the timing) and wanted 300 to fix it. I went to a parts house and bought a new contact switch for $25 dollars, installed it and everything behaved beautifully.
About 4 hours after the repair the unit simply quit. Wont kick on and the thermostat doesn't seem to be communicating with the unit - I don't hear anything attempting to kick the unit on.
I double checked all the connections for tightness, and all appears to be good.
Any ideas? Would appreciate it.
Thanks!

 

[Git]

I am not a HVAC expert by any stretch of the imagination, but I know enough that if my ac won't turn on - first thing I check is to see if the capacitor is bulging. I have had to replaced several over the years. ( But note, a failed capacitor wouldn't cause your ac to stop running)

 

[Dutchmanaz]

The unit won't even turn on (I did visually check the capacitor and it seemed ok). I've got a call out to an AC shop but hoped I could figure it out before they call and tell me they're on their way.
Thanks Git.

 

[Milton Shaw]

First get a flashlight and turn the disconnect off and check each wire connection to make sure it is tight and good , its easy to overlook one when you are doing quite a few.. Then get a DVM meter and check the voltages. You should have 240 volts between the two wires coming into the switch from the disconnect and 240 volt coming out of the switch. The wires to control the contactor should have 24 volts on them. Somewhere you are loosing the voltage to operate the unit. If you have 240 volts on the compressor side of the contactor then you need to get some help. Be careful if you are not used to working with live circuits stop and get help. A

 

[Jim greengo]

If the contactor isn't pulling in check the low voltage wire connections 1st.
Do you have a picture of the contactor?

 

[Dutchmanaz]

Just finished up with the AC guy. I called a different company that we used for the maintenance because this isn't the first time we have had issues after maintenance, so I was a bit suspicious. New guy came and checked my work, and everything was fine outside. He checked the air handler up in the attic and wasn't up there for more than 30 seconds when the unit began to run properly. He came down and said there was a switch on a door up there that had been bent pretty badly preventing the circuit to close and kick on the compressor. The only thing he could think of was something vibrated enough to open the door enough to open the switch, which shut power off to the outside unit. He wouldn't come out and say it, but he said at best this being bent was caused by gross incompetence, and at worse, he said use your imagination. He checked my original contact switch and said it looked ok and wasn't the root cause of my issue.
Thanks for all of the feedback. He did say my compressor fan was running at max capacity and it would need to be replaced by start of summer. He said it was something I could do myself easily enough if I felt up to it. The compressor itself is still running fine for a 15 year old unit.

 

[99LeCouch]

Got bit by one of those fail-safe switches too. The latch holding the access panel shut on our furnace was bent enough to look okay from the outside but not engage the switch.

Compressor fan isn't too bad. Snag a model number off the current one and order it ahead of time. Ours died after 15 years or so. Also, replace the capacitor at the same time. No guarantee the current one will work with a new motor.

 

[Aileron]

max capacity on the condenser fan??? That's usually how they run, as the blade shouldn't change pitch. I call BS and a upsale, unless the bearings are noisy. And I'll say it, the first guy didn't put the blower door on right if he put it on at all.

 

[JerryC]

He probably meant drawing Max amperage.

 

[metlmunchr]

He probably meant drawing Max amperage.

True. Could be at FLA or even on the service factor (if the motor has a SF greater than 1.0). Most condenser fan motors have sleeve bearings that typically get tight rather than loose as they begin to fail, and most pull a bit less than the rated FLA as designed if everything's in good shape.

Its worth mentioning that many condenser fan motors with sleeve bearings have ports where the bearings can be oiled. Typically have removable plastic plugs in the ports. If you reach thru the louvers at the fan outlet with a stick or other such high tech tool and give the fan a spin (power off), it should spin freely for several revolutions. If it makes a round or two and stops, that's a good indication of tight sleeve bearings. At that point you can check further to see if they can be lubed.

 

[Dutchmanaz]

He probably meant drawing Max amperage.

Yes - that's what I meant. Thanks!

I'll check into seeing if the fan can be lubricated too.

Thanks everyone!

 

[fitter30]

If you replace a condenser fan motor with a generic one Do not replace it by hp. Manufacturers have these motors built for them. Replace by amperage if its a 5.1 amp motor replace it with the identical amperage or larger never go even .1 amp less. It will trip out on it's overload.

 

[JerryC]

Did any of the techs clean your condenser coils?
If they are clogged or partially clogged that could increase the load on the fan.
I had a fan motor burn up due to that, actually two but I only paid for one. The company that replaced it thought the coil was clean enough but the new fan motor got too hot and burned up like the first in just a couple of days.
I looked at the coil and I thought it looked OK until that foaming cleaner went on it and the stuff it pushed out was surprising.

 

[Dutchmanaz]

Yeah - I have them cleaned twice a year here in dusty Arizona, so that shouldn't be the issue. The units are about 16 years old so I think a fan motor getting a bit tired shouldn't be that much of a stretch.
What kind of oil should be used as a motor lubricant. Something like 3N1 or the like?

Thanks again for everyone's assistance. This place/people are a great resource.