relay opens immediately on condenser unit - http://www.hvacmechanic.com/ Forums
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| theduke03
 |  "Re(1):relay opens immediately on condenser un"
, posted Tue 3 Jun 18:46  
You may have a borderline low charge causing a low pressure switch to open in that circuit. Do this: When 24v to contactor drops out check low voltage connections to unit(Y and C) for 24v. If 24v is present to unit but not to contactor then I'd say it's low.
I could be wrong so do this too: Turn on a/c. After it's been running for 10 minutes(nonstop) feel the suction line(that's the larger copper pipe connected to unit). Tell me how it feels.(warm, room temp, cool, beer can cold)
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Houston204
| "Re(2):relay opens immediately on condenser un" , posted Tue 3 Jun 19:13
I've seen old mercury bulb stats pop into the demand position causing the mercury to dance around in the bulb. The timer then locks out the condenser for 5 minutes, due to the short cycle condition created.
This would appear to fit your condition except for the fact that you stated "Often it stays closed this time".
It would always stay closed after 5 minutes if this was your problem. A digital stat would have been any easy and attractive solution.
"Tip of the Day" Remember to remove power first.
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| | theduke03
| "Re(3):relay opens immediately on condenser un" , posted Tue 3 Jun 19:32
Houston, I never would have thought of that in a million years. That is some deep troubleshooting. Thus I am now wiser, thanks dude!
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Houston204
| "Re(4):relay opens immediately on condenser un" , posted Tue 3 Jun 20:11
My inlaws house does that every time it cycles.
Do you think I should tell them?
"Tip of the Day" Remember to remove power first.
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| | theduke03
| "Re(5):relay opens immediately on condenser un" , posted Tue 3 Jun 20:21
Only if they're gonna pay you to install a new digital stat. (v-pro of course). I would think that's not gonna happen cuz it would have happened by now if that was the case.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Houston204
| "Re(6):relay opens immediately on condenser un" , posted Tue 3 Jun 20:52
Free, I assure you.
"Tip of the Day" Remember to remove power first.
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| | jbenni
| "Re(7):relay opens immediately on condenser un" , posted Wed 4 Jun 09:00
Good stuff, thank you Duke and Houston!
Duke, once started the unit cools well - with no evidence of icing. The suction line is about "beer-can cold". Even so, your suggestion gives me a good approach to check the low voltage further.
Houston, it's a digital stat, but a cheap one. I like your theory that there's an intermittent signal and the timer locks out the condenser. That fits nicely with the 5 minute delay before it works.
I think I'll run a test: jumper the Tstat out of the circuit, and see if I get a clean start. If not, I will pursue Duke's theory and check the low voltage signals to see where the signal stops, checking pressure (and the low pressure sensor) as followup steps.
Houston, good luck with the inlaws and let us know if you have any success getting paid for your work!
You guys rock, thanks a ton.
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| | theduke03
| "Re(8):relay opens immediately on condenser un" , posted Wed 4 Jun 18:52
You're welcome 12,000 BTU's.
"My dad was the most feared furnace fighter in Northern Indiana."
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