heat pump troubleshooting
My new, 2nd floor heat pump is acting up. I had it commissioned in May, and it worked fine for the summer and the first part of the winter. Lately, it’s developed the habit of getting stuck in defrost mode. More like fake defrost mode, because no defrosting happens (according to the energy monitor). I can get it out of this mode by setting the temperature to maximum. This seems to wake it up, and after 15 minutes or so it finishes the defrost cycle and starts heating again, at which point I return the temperature to the desired setting.
I contacted the retailer, and the guy who replied to me thinks it’s low on refrigerant. I’m a little skeptical of this because of the intermittent nature of the failure. Sometimes it can go a week working fine, then all of a sudden it gets stuck in the fake defrost mode once or twice in a day for a couple days in a row. It’s not load or outside temperature related, as we had a mix of temperatures over that week it worked fine, down to -18C. They also have a vested interest in pointing to a refrigerant leak, as it puts the responsibility on someone other than them.
I haven’t contacted the guy who did the commissioning yet, who is unaffiliated with the retailer. I’m anticipating a scenario where each party says it’s the other one’s fault. This is the price I pay for doing it this way, but it did save me about $3000.
At the retailers behest, I checked the temperature of the large copper tube at the outdoor unit after 30 minutes on max, and it was too hot to touch. It was also making some sounds, kind of like gurgling or boiling.
它是苏nd like low refrigerant is a likely cause?
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Replies
Sounds like you have a leak especially if you are hearing gurgling. Is this a multi split or single unit? I would measure your delta T (difference between supply and return) at max speed and post your results.
I have electricity monitors on all my splits. Here is what the defrost cycles look like on my energy monitor
I don't have a tool that would accurately measure those temperatures. I think my defrost cycle, when working, looks similar. When it's stuck, it's a continuous 30W or so. I guess I will ask the installer to come out and have a look.
Any thermometer will work like a digital meat probe one. You can actually get a really good performance number off the electricity consumption and the delta t. You set the fan to high and look up your units CFM at high and you can roughly calculate its btu and cop output.
The formula for BTU is Temp differential times CFM times 10% - Example with a CFM of 325 delta t of 34.
CFM of 325 x 34F = 11050 x 10% = 12,155 btus.
During a defrost cycle the compressor doesn't actually stop. At least on the 5 mini splits of different brands I monitored. If your seeing just 30 watts then the compressor isn't running. Is there a defrost Indicator that's on? All my units will show on the led screen if its in a defrost cycle.
I can't visualize how the temperature probe would be placed so that it was reading mostly the pipe and not the cold air all around it. The point of contact would be awfully small.
Yes, there's an LED marked Fan/Def. It's kind of a weird setup where the wall thermostat goes to a little control dongle with a manual test switch before connecting to the indoor unit.