Heat Pump False Starts and Eventual Failure

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Old 01-09-20, 01:12 PM
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Heat Pump False Starts and Eventual Failure

Hey All,

I monitor my home's electricity usage and can see live current draw. For months now I noticed that whenever the heat/blower turned on, there was a strange current profile that looks like this:


https://imgur.com/a/SZP1cui

It's not always exactly 5 startup attempts, sometimes 3 sometimes just 1, usually starts within a minute. I wasn't sure if it was the blower or heat pump, and if it was just some weird in-rush current profile or what, but 125A sure seems high. Unfortunately I didn't get a professional to look at it soon enough, although it is tough to explain this kind of problem over the phone.

Fast-forward to this morning, when the heat started to turn on, the lights flickered (never happened before), a few seconds went by, the lights flickered again, then I heard a loud pop and hiss from outside, the heat pump hissed for about a minute then stopped. I can only assume the condenser or a line broke, and all the Puron leaked out. It's a 2012 Carrier, model 25HBC342W300 for those playing along at home. I immediately turned off the heat pump breaker, then opened up my power monitoring tool to see what happened, it looked just like the picture above except the heat pump never actually came on, and the peak current was 43kW which is 180A!!! No wonder the lights flickered. Any ideas for what kind of failure mode this is? I'm getting someone to come look at it soon, but I figured this forum was a perfect place to share the current draw screenshots and seek advice. I don't want them to replace a part, refill with Puron, then have it keep happening.

Note that my heat pump has been running at a duty cycle around 50% the last several days, nothing too crazy, and when this happened the outside temp was 35 F and sunny, it's been way worse. I keep it free of leaves/weeds.

-Marc
 
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Old 01-09-20, 03:11 PM
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May have been a starting component failing. Or a TXV issue.
 
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Old 01-09-20, 07:17 PM
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You've monitored that multiple spike issue for months.
Had you ever stood outside by the condenser when it was trying to start ?
I would agree on a start component or possibly low on refrigerant and cycling rapidly on low pressure. It should have been very easy to hear.

Now.... it sounds like the compressor may have blown apart.
 
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Old 01-09-20, 10:09 PM
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I should have mentioned I know very little about HVAC, but this incident will certainly force me to learn more about it, I'm not going to try to fix it myself but I like to know how things around me work. I noticed the current draw was strange but thought it was just the blower motor's in-rush current or something, until today when the condenser clearly broke. I didn't spend months monitoring this specific issue, I just recall that I noticed the weird current pattern at least many months ago, possibly even since I installed the whole house power meter. If anyone's curious- it's an "Eyedro" home electricity monitor that connects to the internet over Ethernet, comes with one current Transformer for each phase, I love it. And now I know to dig a little deeper when something looks fishy. Hopefully it's just one part that needs replacing =/

I've got an HVAC professional coming in the morning, I'll let you guys know what he says. Thanks for the comments so far, all are appreciated!
 
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Old 01-10-20, 05:14 AM
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Assuming the time base on the plot is linear, the breaker for the heat pump should have tripped because the current is about 100A for seconds multiple times. What type and rating is this breaker?
 
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Old 01-10-20, 01:51 PM
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Yep the time domain axis is linear and labeled correctly, there was like 20ish seconds between the instances of trying to start. But note that because of the way these power meters do time averaging/time smoothing, you can never really tell the duration of a burst, i.e. the burst might have been higher and not very long, and it probably wasn't as rectangular as the plot shows. But you make a great point, the breaker should probably trip, especially during the last occurrence where the heat pump broke, so I'll go ahead and replace that breaker just for good measure, since like I mentioned I'm an electric guy not an HVAC guy.
 
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Old 01-12-20, 12:46 PM
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I found the issue! HVAC guy I called never showed up, so I took a look myself, turns out the compressor's plug blew out, it was just hanging next to it, and one of the pins was inside the plug, I took a bunch of pics- https://imgur.com/a/Hty81b4 I assume that's not a repairable thing, and the compressor needs to be replaced? Considering it will need a new compressor, AND there is still some issue with a starting component, seems like I should just replace the whole unit. It's an 8 year old unit. What do you guys think?

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Last edited by PJmax; 01-12-20 at 12:53 PM. Reason: added one pic from link
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Old 01-12-20, 12:54 PM
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Correct..... that is not a repairable thing. The compressor needs to be replaced.
There is no refrigerant in the system now either.
 
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Old 01-12-20, 01:45 PM
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I'm trying to see how big an outdoor unit I would need to replace it with. My current one is 13 SEER, but I don't see a ton or kW rating anywhere on it or even in the product datasheet. It's a Carrier 25HBC342W300 and the product info is here- https://www.shareddocs.com/hvac/docs...25HBC3-3PD.pdf it's the "42" variant. Factory charged at 8.88 lbs. Do they just not provide those numbers because they are estimates not specs?
 
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Old 01-12-20, 01:52 PM
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It’s a 3.5 ton, that’s what the 42 is.
If that unit was registered it could still be under warranty.
 
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Old 01-12-20, 02:00 PM
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Yeah unfortunately I'm not the original owner, I bought this house a couple years ago, so doesn't matter if the original owner registered it or not. Ty for pointing out it's a 3.5 ton! Would this be a good replacement? https://hvacdirect.com/3-5-ton-14-se...heat-pump.html I would talk to whoever I get to do the install before purchasing it.
 
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Old 01-12-20, 02:23 PM
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The mismatched units could lead to a problem, with it being a heat pump.
If it were straight ac it wouldn’t be that much of an issue.
 
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Old 01-12-20, 02:51 PM
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Ah, thanks for pointing that out, I just found https://www.cooltoday.com/blog/is-it...ils-dont-match which explains some reasons why they should match. Now if I found a 13 SEER 3.5 ton, would that make it more OK to replace just the outdoor unit?
 
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Old 01-12-20, 09:16 PM
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A little better.
Although without an AHRI match number the actual efficiency and capacity will be unknown. But it should work.
 
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Old 01-12-20, 11:39 PM
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Thanks for pointing out AHRI matching, I'm learning so much ! Looks like my indoor unit is a FX4DN(B,F)043L, and ahridirectory.org doesn't show it paired with my SEER 13 heat pump (25HBC3), but it shows it paired with a bunch of SEER 14 and 15 combos, like the Carrier 25HBC5 aka "COMFORT 15" heat pump. So I'll just try to buy one on that list, that is in the 41k - 42k heat/cooling capacity range.
 

Last edited by 777arc; 01-13-20 at 12:06 AM.
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