Mini split condenser fan intermittent
Hi all, I've got a 3 ton Panasonic mini split in my shop with a single head that was installed about 5 years ago. I typically only use it for shoulder season heating, but will occasionally use it for cooling as well. It's always done just fine heating, but the cooling only works decent if I fiddle with the remote a dozen times and crank the temp down to 60*. It's done this since new and I never really cared enough to get into the "why", but yesterday I noticed while mowing lawn that the condenser fan was turning very slowly despite a 71* setpoint and 76* air temp, then wasn't turning at all for a brief period. The condensate was dribbling and both lines were cold so it seems to be working, but it ran like this for 12 hours and only cooled the space down 1*. I changed the settings for the head to run on high which it did (no auto), but the condenser fan just kind of did whatever it wanted and didn't seem to care that it had a job to do. I'm in the pipe trades and have asked several of my colleagues in the HVAC side of things what this might be and it has been a unanimous "hmm, that's weird" but nobody wants to even come look at because they don't know what to look at/for. It seems to me that there is a command that's not getting sent, somewhere in the system. Again if I crank the stat way down, everything works like it should but when it gets anywhere near setpoint, the condenser fan slows WAY down or even stops. Can anyone shed some light on this for me please or give me something to check?
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I don't know what size motor is on the outdoor unit but we had some cooling fans for equipment racks where the manufacturer used a variable speed control that had a pwm output for the dc fan motor but did not filter the output of the pwm control so the fan would just make whining and chirping noises until the rack warmed up enough to call for close to full speed cooling. If you looked at the 12v supply to the pwm control with a scope you could even see the square wave on it. In this case a filter cap on the pwm output solved the problem but this was a maybe 10w or so fan and was driven directly by the output of the pwm control.
The liquid line should be hot or at least at ambient until it gets to the refrigerant control.
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Slow odf is normal approaching set-point but off is odd. I don't know Panasonic well so hard to give advice on it. At year 5 I'd want to see that refrigerant pressures match performance charts on high. Does the compressor frequency match the fan? Is your indoor coil and filter clean? A fouled/faulty sensor or clogged air path can fake the control in to thinking it's doing good work when it's not and the system just slows down seeking efficiency. The remote is not a temperature sensor. It's just a programmer. The gas peddle sensor is at the coil return air if it fails gets wet or is dust bunny covered the control has lost connection with the room.
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I have no idea what the pressures or frequencies are. The coil and filter seem to be clean, but it's done this since brand new and I've never gotten any amount of dust or debris out of it. It is in a shop environment so there is some dust being made, weld smoke, etc but this thing only gets turned on maybe 15 days a year so it's not like it's a constant barrage of yuck being sucked through it. Perhaps I'll open it back up and try to locate this sensor you speak of and check it over. I don't have a manual for it and can't recall the model anymore, but I should be able to find some sort of diagram online to help out to some degree. Thank you!
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It's not blowing at a wall or something that would throw off the air temp sensor is it?
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if oversized that fan WILL cycle on and off depending on the inside load.
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I have noticed that we Americans find the way the Japanese handle space conditioning programing logic odd. I tell new owner to give it a little more time to do it's thing it's programed to go easy. We say we want it to be 71F and it's not trying hard enough it's 74F after all. Get to work you lazy machine. What's it waiting for? I've tested fans with tech support before but haven't found one faulty yet.
You can hear the compressor whirling at different pitches as it ramps up and down being driven by the inverter with high and low frequency. The ODF generally follows the compressor speed. You can test it by setting set point very low noting the sound as it ramps to full power and step by step moving set-point closer to actual and noticing the speed steps it goes through to minimum. If the two move together they are probably working right and it's something else. Is it possible that the air entering the indoor fan unit is not 76F but is closer to 71F and that's why it's ramping down to low and off. Or that the cover wasn't fitted right and cold post coil air recirculates cooling the sensor or the sensor got dislocated from it's designed location. The wall unit only knows the air that enters it. The remotes have no sensors. Generally they don't tell you the current temperature. Where are you measuring that? Could it be a calibration difference?
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No
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It's not oversized at all, especially when there's a constant 6* deficit to cover.
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All valid points! I was under the impression that the ability to turn off the "auto" function was effectively an override for the "get to work you lazy machine" people, which in this case, I am. When in auto, it'll idle all day and eventually get where it needs to go, but typically if I push enough buttons it will consent to doing what it's capable of. I can't hear the compressor at all and never could, but maybe I'm just hard of hearing. It would stand to reason that the two are synced, but I'd find it hard to believe that the compressor is stopping along with the fan while there is a tremendous load on the other side of the wall. I do suppose it's possible that the inlet sensor is picking up a cooler temp than actual, but I have a thermometer on the wall 2 feet from the head and another across the building 40 feet away which both are within 1 degree of the remote's reading regardless of the remote's location in the space so I'd like to think that's not the case. I have not had a chance to open it up again yet, but I will certainly keep you posted when that happens. Thanks again!
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Be sure fan is tight on the shaft.
(Much trouble at work from neglected fan belts.)
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