MRCOOL air conditioner P6 error code: low pressure protection
Also shown as PC 03
- Urgency
- High
- Who can fix it
- Moderate DIY
- Time
- About 30 min
- Repair cost
- $250–$1500
What the P6 code means
On Gen 4 and Gen 5 MRCOOL mini-splits, PC 03 (also shown as P6) means low pressure protection has tripped. MRCOOL says it is usually a restriction in the system or low charge, and on new installs a closed valve or loose line-set connection.
Low pressure on the suction side means too little refrigerant is reaching the compressor. That can be because a valve is closed, a tube is kinked, or refrigerant has leaked out.
On a new DIY install, valves and connections are the first things to check. On a system that had been working, a leak is more likely.
Common causes
Listed from most to least common.
- Service valves not opened all the way on a new install
- King valves on a multi-zone condenser left closed
- Line-set connection loose and leaking
- Restriction in the system, such as a kinked line set
- Low refrigerant charge from a leak
- Pressure switch stuck open
How to fix the P6 code
Unplug the air conditioner or switch it off at the breaker before removing any panel or filter.
Step 1: Turn off the power
Switch off the breaker and disconnect for 15 minutes before checking anything.
Step 2: Open the service valves fully
MRCOOL says to open the service valves all the way to the locking ring, then snug them slightly. On multi-zone units other than dual-zone Gen 4, also open the king valves on the two vertical lines.
Step 3: Tighten the line-set connections
Check every connection at the air handlers, condenser and couplers. No threads should show.
Step 4: Check the line set for kinks
Follow the line set along its route. A sharp kink can choke refrigerant flow and cause low pressure.
Step 5: Book a pressure check
If the code returns, a technician should connect gauges and check pressures.
You'll need: Allen key (hex) wrench set, two adjustable wrenches, flashlight.
How to reset the MRCOOL air conditioner
- Turn the mini-split off with the remote.
- Switch off the breaker for the system and the outdoor disconnect switch. MRCOOL suggests leaving the power off for 15 minutes so the boards fully reset.
- Restore power and turn the unit back on. The compressor normally waits about 3 minutes before starting, so give it time before judging.
- If the same code comes back straight away, the fault is still there. Work through the fix steps above, or call a technician.
When to call a technician
Checking pressures and fixing a leak or restriction needs a licensed HVAC technician with EPA certification. Never add refrigerant yourself.
A typical repair for this code costs $250–$1500 in the US, including parts and labor. Prices vary by area and model.
Models this applies to
- DIY Series ductless mini-splits (Gen 1 to 5), single-zone and multi-zone
- Advantage Series mini-splits
- Olympus Series mini-splits
- EZ-PRO mini-splits
Codes can differ slightly between models. Your owner's manual is the final word and is available from MRCOOL support.
Frequently asked questions
›Is P6 the same on every MRCOOL?
No. On Gen 1 to 3 indoor units, P6 means too much or too little refrigerant. On Gen 1 to 3 multi-zone outdoor units, it means an inverter module fault. Gen 4 and 5 use PC 03 or P6 for low pressure.
›Can I fix a kinked line set?
Contact MRCOOL support first. MRCOOL has a support article on kinked line sets, and a pinched tube may need replacing. Do not try to straighten it with force.
›Should I tap the pressure switch?
MRCOOL mentions lightly tapping a stuck pressure switch, but it sits inside the outdoor unit near live parts. Leave that to a technician.