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How to test AC relay and condensers?

Posted: Tue Jun 11, 2019 6:30 pm
by A. Spruce
Hey guys,

104F here today and the condenser/fan (outside portion of unit) quit running. When I flip the breaker, I can hear a click at the unit.

There are four items between the incoming power line and whatever magical components are beyond, there is a buss block the wires attach to, then a relay, then what appear to be two condensers/capacitors. How do I test to see where the problem is without electrocuting myself?

It's been fine until about 3pm when the thermostat settings seemed a bit wonky. Didn't think anything of it, but two hours later the temp is rising. We have reached the peak forecasted temp for the day, so it's going to be 5 or 6 hours before it's cool enough to open up the house for natural cooling.
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Re: How to test AC relay and condensers?

Posted: Tue Jun 11, 2019 11:21 pm
by A. Spruce
HVAC tech called back at 9pm, we're scheduled for Thursday, but they'll try to sneak us in on Wednesday.

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 2:46 am
by Aaron
Good luck, the components in the condenser are out of my league. I know you should have 24 VAC coming in on the signal line (from your furnace) to get the condenser to run. Make sure it's also getting 240VAC to run (check your outside fuse box).

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 7:44 am
by emtnut
A. Spruce wrote:
Tue Jun 11, 2019 6:30 pm
Hey guys,

104F here today and the condenser/fan (outside portion of unit) quit running. When I flip the breaker, I can hear a click at the unit.
Since you can hear a 'click' , that is most likely the contactor pulling in.

See pic, measure for 240V there. You may have popped a breaker, which may indicate a bad compressor ... but reset it , and see if it pops again.

If you are looking at the contactor when it engages, you will actually see one side move (pull in).

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 8:35 am
by A. Spruce
breaker was the first thing I checked, it was not tripped, I tripped and reset it just to be sure, and could hear a click in the unit as I did so. The unit is 2 feet from the breaker, but these here parts is on the opposite side, so I can't see them and flip breaker at the same time. Helper won't go outside when it's 103* either! :roll: :lol:

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 9:51 am
by emtnut
A. Spruce wrote:
Wed Jun 12, 2019 8:35 am
breaker was the first thing I checked, it was not tripped, I tripped and reset it just to be sure, and could hear a click in the unit as I did so. The unit is 2 feet from the breaker, but these here parts is on the opposite side, so I can't see them and flip breaker at the same time. Helper won't go outside when it's 103* either! :roll: :lol:
If you have a multimeter, you can measure to see if you have 240V (at those arrows)
If you do, then measure between the top 2 terminals of the contactor and you should have 240V.

Since the breaker didnt trip, I doubt it's the compressor ... but either low on freon or the pressure sensor is bad.

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 1:27 pm
by A. Spruce
Tech had an opening and will be here within the hour. We'll know for certain shortly. 8-)

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 3:17 pm
by A. Spruce
The disconnect was a little melted and the capacitor was bad. We gots cold air now! 8-)

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 3:56 pm
by emtnut
A. Spruce wrote:
Wed Jun 12, 2019 3:17 pm
The disconnect was a little melted and the capacitor was bad. We gots cold air now! 8-)
Good to hear ... you're hard enough to deal with at room temperature ... I wouldn't want to see what happens when you heat up :mrgreen:

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 4:04 pm
by A. Spruce
emtnut wrote:
Wed Jun 12, 2019 3:56 pm
A. Spruce wrote:
Wed Jun 12, 2019 3:17 pm
The disconnect was a little melted and the capacitor was bad. We gots cold air now! 8-)
Good to hear ... you're hard enough to deal with at room temperature ... I wouldn't want to see what happens when you heat up :mrgreen:
It takes a lot more than a little heat to make me grumpy, say, heat and no adult beverage refreshments, now THAT would make me a tad bit testy! :evil: :lol: :lol:

$422 seems a bit steep, but money well spent when the temps breach triple digits. It was $142 in parts, $280 in labor (2 hours). Maybe I need to get back into the biz, $140 bucks an hour adds up quick! I even set up a shade umbrella and a big glass of ice water so he wasn't melting under the burning sun! I'd hate to see the bill if I'd have been mean! :o :? :lol:

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 7:33 pm
by Aaron
$422!!! That's highway robbery.

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 7:56 pm
by A. Spruce
Yeah, I wasn't going to complain because they did wiggle me into their schedule so that I wouldn't be without AC for too long. You do pay a premium for such things, though I don't think I was charged any surcharge or "emergency" price for the work done.

Re: How to test AC relay and condensers?

Posted: Wed Jun 12, 2019 9:03 pm
by Aaron
Those parts have like 3000% markup. :(

Re: How to test AC relay and condensers?

Posted: Thu Jun 13, 2019 9:45 am
by emtnut
I'd say closer to 300% markup on parts, but that's pretty much standard. It takes time to stock and store all the various parts that are needed.

I'd say $140/hr is fair as well. Contractors have licensing, insurance, vehicles,tools, advertising etc etc, costs to pay for. They also usually can't bill for 8 hrs day/ 365 a year also.


At least the guy was honest, ... You hear stories of them trying to sell new compressors !

Re: How to test AC relay and condensers?

Posted: Thu Jun 13, 2019 1:42 pm
by A. Spruce
emtnut wrote:
Thu Jun 13, 2019 9:45 am
At least the guy was honest, ... You hear stories of them trying to sell new compressors !
Yep, this was actually a topic of conversation while he was working. He was meticulous, clean, and did good work. He showed me how the disconnect was warped from being too hot and the capacitor was bulged, indicating that it was bad. Changed both items, we got cool air immediately. While it was a bit more than I expected, I'm happy to have AC back, so I ain't complaining . . . too loudly. :mrgreen:

Re: How to test AC relay and condensers?

Posted: Thu Jun 13, 2019 3:39 pm
by Aaron
Almost would be worth it to replace those parts on suspicion, shot gun troubleshooting...

I replaced a cap for my furnace blower last summer and I think it was like $15.

Turns out the old cap was fine, the fan motor was toast. So a new motor cost me like $120, and came with a new cap anyway.