Mini Split sensor check

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Old 02-19-15, 05:58 PM
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Mini Split sensor check

Are there specific sensors that will limit the compressor speed in a variable speed heat pump. My heat pump will only run at half speed (based on amp draw) no matter what the indoor or outdoor temp is.

I can get it to run at a lower speed if I set the indoor thermostat below room temperature. Without running at full speed, there is not enough heat output to warm up the house.

Pulling the indoor pipe sensor allows the compressor to run at full speed but will not allow indoor fan to run. Is there another sonsor in the outdoor unit I should be checking that would cause the same issue?
 
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Old 02-19-15, 08:59 PM
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Since we have no idea the make or model of your system we'd just be guessing.

I'm sure there are sensors but locating and modifying them could be an issue.
Have you tried asking the installer or contacting the manufacturer to see what the proper operation is ?
 
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Old 02-20-15, 06:26 AM
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It is a Senville Aura 18000btu ductless mini split I installed the unit myslef without issue. The local HVAC contractors are backed up for about a month so I am taking it upon myelf to see if I can narrow down the problem.

I did contact the company and they gave me the procdure to check the control boards. They told me to check the DC voltage between L2 and S, and that it should fluctuate between -50 and +50 volts DV. I did the check and it fluctuates around -30 and +10 Volts DC. They seemed to take that as normal. Other than that they have not been much help and suggested I get an HVAC tech to come look at it.
 
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Old 02-20-15, 07:49 AM
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I'm looking over the service manual. So far I don't see anything you can change to affect the operation. I'll keep checking and report back.

senville/downloads/ServiceManualForSenvilleAirConditioners.pdf
 
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Old 02-20-15, 07:52 AM
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Thanks. I have read the service manual also and dont seem to see anything really useful. There is information about under what conditions the compressor ramps up or down, but I dont entirley understand it all.
 
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Old 02-20-15, 02:24 PM
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It is not normal for a compressor to be pulling the RLA value listed on the nomenclature.

Is this unit heating the space to setpoint?
 
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Old 02-20-15, 03:43 PM
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Not even close to heating to the setpoint. At -10c I cant get the house warmer than 15c. I am heating about 1,000 sq ft with modern windows and insulation. It is rated to heat to -20c, and had others tell me theirs worked great even at -25c. I had originally bought a 12,000 btu of the same model, and while it worked fine, it was just undersized for the space, which is why I went to an 18000, but this one is not heating as good as the last one. There is definitely an issue somewhere, and I would like to try and figure out if it is just a bad sensor or what before paying a tech to figure it out. They are all booked solid for the next month anyway so it's not much help to me right now.
 
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Old 02-20-15, 03:57 PM
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I'm guessing the unit is out of warranty.
Did it used to heat better or was it always like it is now ?
 
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Old 02-20-15, 04:05 PM
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I usually contact tech support when trouble shooting mini splits.
There are differences in diagnosing these units that are not present with standard HVAC equipment.
 
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Old 02-20-15, 04:48 PM
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The unit is new, installed myself with the help of someone who does hvac installs. He knows the install procedures but doesn't have the knowledge to diagnose problems. System was leak checked and vacuumed to 400 microns. It has been like this since installed. I have contacted tech support but they have not been very helpful so far. Basically just gave me the procedure to check the boards and asked if i have had a tech out and what they thought the issue was. As I said, it will be a month or more before I am able to get a tech here.

I had the gauges hooked up the other day and took these measurements if they are helpful.

Inside temperature 66F
Outside Temperature 14F
Suction temp at 3 way valve (big line) 150F
Liquid temp at 2 way valve (small line) 86F
Pressure at 3 way valve in heat mode 340psi
Draw from compressor 5.7 amps
Output temp from Head 95F

Could it just be under or overcharged?
 
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Old 02-20-15, 06:31 PM
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You need to weigh in mini split charges. We are not allowed to give charging instructions.

It is tough to charge standard heat pumps in heat mode. A mini split is worse.
 
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Old 02-21-15, 03:42 AM
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I understand that and don't want to know how to charge it myself. Just if it possible the charge is not right based on the information provided. The unit came precharged so i can only assume it might not have had the right charge from the factory.
 
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Old 02-22-15, 09:11 AM
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Anyone able to give me some more insight on this? In addition to pulling the indoor pipe sensor forcing the compressor to put out more heat, I noticed that if I run hot water over the outdoor air temp sensor, the compressor will shut off entirely. Are htemperaeat pumps designed not to work in heat mode at all ambientambeant ture is too high?
 
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