Mitsubishi Mr. Slim MXZ30TN Air Conditioner

Mitsubishi Mr. Slim MXZ30TN Air Conditioner Owners Manuals, User Guides, Instructional Help Documents & Operating Information - MrSlim_P-SERIES_Troubleshooting_TIPS.pdf

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July 7, 2005

Mitsubishi Electric ‘Mr. Slim’ P-Series Commercial Models

TROUBLESHOOTING TIPS / P8 ERROR CODE These systems have very sophisticated microprocessor control systems to operate the system efficiently and to protect it from conditions which could lead to damage. If the P8 Error Code appears on the wall controller this indicates a problem with the condensing (outdoor) unit. There are several possible causes for this fault. A few are mentioned in the literature provided by Mitsubishi, but experience has shown that many other conditions can also result in the P8 Error Code. 1. Is there power to the outdoor unit? P-series indoor and outdoor units are typically wired from separate sources. On cooling only units the indoor section is 120/1/60 volt and the outdoor section is 208-230/1/60 volt. On heat pumps both sections are 208-230/1/60 volt. The indoor unit could have power to it but not the outdoor unit, resulting in a P8 fault. 2. Is the 2-wire 12 VDC communication link between the indoor unit and outdoor unit intact? This wiring is polarity sensitive so if the wires are crossed, shorted or broken this is also a problem to look for. Ensure the wires are secure in the terminals as well. Loose wiring can cause intermittent problems. 3. There is a 208 Volt jumper for the outdoor unit control board. Verify your power supply voltage and insure this jumper is correct for what you actually measure at the unit with your meter. The outdoor board monitors the power. 4. The outdoor board monitors the temperature of the refrigerant leaving the condenser coil and modulates it’s condenser fan(s) to try and maintain a 95°F temperature. If the discharge temperature gets too high, or too low, the unit will shut off. Verify that the pipe temperature thermistor is not open or shorted, and that it is snug in the well attached to the refrigerant pipe. 5. Is the condenser fan operating? On the extra low ambient models (-40°F) there is a control to disable the condenser fan(s) during very cold weather. If this control is defective it may be preventing operation of the fan(s) in warm weather. Ensure the condenser fan is ramping up to full speed when required. 6. Is the unit operating year-round but not a -40°F low ambient design? You can determine this easily because the accumulator on -40°F units is heated and insulated. Ensure the accumulator heater is functioning in the winter. 7. Is the system undercharged, or overcharged? It is a capillary tube metering device so the refrigerant charge is critical. P-series units have an accumulator which enables it to store enough refrigerant for up to a 100’ line set. After 100’ additional refrigerant must be weighed in based on the total 1-way lineset length. Please refer to the attached pages from the Service Manual for more information on troubleshooting.

21 Grenfell Crescent, Suite 1 Ottawa, Ontario K2G 0G3

Phone: 613-723-0359 Fax: 613-226-4892, Toll Free: 1-888-279-2505

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1. OUTLINE OF MICROPROCESSOR CONTROL INPUT to remote controller ● OFF-ON switching. ● COOL/DRY-FAN selector switching. ● Thermostat setting. ● TIMER mode selector-switching and Timer setting. ● HIGH-LOW fan speed switching. ● AUTO Vane selector (AIR DISCHARGE) switching. ● TEST RUN switching. ● CHECK mode switching. (Self diagnostic trouble shooting)

● Processes and transmits orders.

OUTPUT to remote controller

Remote controller ● LCD indicator





Non-polar, two-wire cable maximum length 550 yards


Indoor unit

Remote controller board


Indoor controller board INPUT from indoor unit ● Room temperature thermistor (RT1) ● Pipe temperature thermistor (RT2)

OUTPUT to indoor unit

● Receives orders from remote controller and temperature data from indoor unit. ● Processes orders and data. ● Controls indoor and outdoor operation. ● Self diagnostic function. w System control operation. w Emergency operation. w Set by dip