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Compressor shutting down

Just installed a Grunaire GMU243HX ductless heat pump with two air handlers. I had to cut the lines for a neater installation. The system started up and ran for about 10 seconds then shut itself down. Initial start up pressure on the low side was 100 psi. Not knowing what the line pressure should be I assumed that the system was overcharged due to shortening of the freon lines. I bled some charge off of the system but it kept shutting down and restarting every 3 minutes. The indoor unit displays an error code of FC. I have checked the line voltage and it is a little high at 243 volts. The installation says max 220 but usually there is a 10% variance acceptable on line voltage. Obviously, there is a safety shutoff feature that is shutting the system down or the compressor would not kick on. Any help would be appreciated as Grunaire's assistance is still forthcoming.

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  • vyoral Apr 25, 2010

    I failed to mention that the system is R410a. I think that with ambient air at 85 deg, the pressures should be 100-130 low side and 400-430 high side. The unit only has a low side test port. According to the owners manual FC is compressor start failure.



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The ONLY CORRECT way to charge a mini or Multi split unit is to WEIGH in the charge.. these units operate with electronic Expansion valves and there is no high side port on purpose..

Grunaire units are precharged for 25 ft of line on each indoor unit... measure your lineset size and subtract 0.7 oz of refrigerant for each foot of 1/4" liquid line less than 25 feet you have on each indoor unit.. the result is your new charge amount...

the base charge can be found on the outdoor unit Label..

an FC error code can occur for many reasons... a bad PFC board.. (this is the board with the MOSFETS thaty actually drives the compressor)..

over charge can be an issue as well due to high standing pressure resulting in the drive not able to overcome the backpressure to start the compressor...

high line voltage will issue error codes as well... 243 seems high but still normal... make sure each of your legs is equal...


Posted on Jul 26, 2010

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Posted on Apr 24, 2010

  • airdoctorz Apr 25, 2010

    Seems a little high with temp at 100- 110 you would be red line on hot hot  day. we have those days in high desert . most of my 410a were at 80-90 on cooler days with no humidity. 



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