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Discussion Starter #1
I purchased a new YMGI unit last year (VRFO-60HP-V2B(55)5). I believe most components in there are manufactured by Gree. Anyways, it's a 60K btu unit servicing 5 indoor units on a single line set that branches off accordingly to each unit. The unit heats as well as air conditions. I have no issues with the AC portion of it but i am with the heating.
Every now and then it goes into defrost mode. Sometimes, even when the outdoor temperature is in the upper 40's/low 50's. Iv been out there trying to verify ice on the coils but nothing. No ice formation yet it still goes into defrost mode. In addition, (not every time) it will stay in defrost mode for 30+ min to the point the indoor units start accumulating frost on their coils. Only way to restore heat is if i turn off all the indoor units with the remote, wait 10 min then turn them back on.
I had my AC guy verify freon and he added 2 lbs to the unit. We did a pressure test and it read stable at 550 psi after about 1 hour of use on heat so i doubt its a refrigerant issue. I doubt its the reversing valve cause that wouldnt be the cause of the defrost turning on when no ice is present on the coils. The manufacturer keeps blaming the issue on the install but i know that's not the case because the majority of the time it's working perfectly so requesting help from them is useless.
I'm thinking either a faulty sensor or control board. The defrost unit is incorporated onto 1 board that also supports the air conditioning. I'm not sure how to troubleshoot the sensors and/or the controller board as im thinking its one or the other (possibly both but not likely) so i was hoping for some direction in this matter. if anyone here feels the issue lies elsewhere... Please feel free to voice your comments.

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Discussion Starter #3
Thanks for the reply.... My sensor does not look like that. It's just a simple probe. that sits on the return line. I guess it checks for the temp line coming back to the compressor and monitors it. It might be bad, i'm just not certain how to test the thermostat with a voltmeter. Need to know what readings to look for. Thanks again for the reply.
 

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Yours will not have the type of defrost switch as in post #2. It’s a thermistor type sensor.
You check them by measuring resistance through the thermistor.
 

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Discussion Starter #5
Thanks for the reply. Does the attached document appear to be correct dependant on the ambient temperature? It shows for 10K Thermistors. Not sure if mine is 10k or not. I can check the resistance of the thermistors with my voltmeter to determine its accuracy assuming the document is correct. What is the rule of thumb as far as tolerance? Im assuming the number isn't going to be on the nose so would +/- 1000 ohms be acceptable?
Also, i wanted to check the board for proper voltage. Upon investigating, the ambient as well as the coil should read 5-6 Vdc off the terminals on the board. Does this sound about right? Unfortunately, i dont have the spec sheet for these items hence i'm wondering if these are universal numbers to go by or is each unit different. Thanks again for the heads up and assistance.
 

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The thermistor is dependent on what kind it is. No real rule of thumb. It should be pretty accurate.
All this information should be available on the manufacturers IOM. Unfortunately I’ve never heard of that brand, and Gree in my experience has been less then ideal for technical literature.
 

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Discussion Starter #7
Understood. Thanks. Will take readings of the thermistor and report back with my readings. i think there are 3 of them in total. One is ambient, one is the coil and im not sure what the last one is for but ill take the reading anyways.
 
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