MRCOOL air conditioner P1 error code: over or under voltage protection

What the P1 code means

P1 on a MRCOOL mini-split air handler means the system has detected supply voltage that is too high or too low and has stopped to protect itself. Gen 4 and Gen 5 units show it as PC 01. Loose wiring, a weak breaker or a supply problem is the usual cause.

Inverter mini-splits are sensitive to supply voltage. If the voltage strays too far from normal, the board shuts the compressor down rather than risk damage, and shows P1.

A one-off P1 during a brownout is nothing to worry about. If it happens often, or every time the compressor starts, the supply or a connection has a fault.

Common causes

Listed from most to least common.

1. Low or unstable voltage from the home supply
2. Loose connection at the breaker, disconnect or terminal block
3. Worn breaker or wrong breaker size
4. 115V unit wired to the wrong supply, or the reverse
5. Outdoor control board fault

How to fix the P1 code

Unplug the air conditioner or switch it off at the breaker before removing any panel or filter.

1. 1

   Step 1: Reset the power

   Turn off the breaker and disconnect for 15 minutes, then turn them back on.

2. 2

   Step 2: Watch for other power symptoms

   Lights dimming, other appliances resetting, or a breaker that feels warm point to a supply or connection problem.

3. 3

   Step 3: Check the breaker and disconnect

   Make sure the breaker is fully on and the disconnect is pushed in firmly. MRCOOL suggests trying a different breaker if the voltage is off.

4. 4

   Step 4: Have the voltage tested

   MRCOOL's guide checks voltage at the outdoor and indoor terminals. That is live electrical work, so have an electrician or HVAC technician do it.

How to reset the MRCOOL air conditioner

1. Turn the mini-split off with the remote.
2. 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.
3. Restore power and turn the unit back on. The compressor normally waits about 3 minutes before starting, so give it time before judging.
4. 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

Call an electrician if the problem is in the house supply, breaker or disconnect. Call an HVAC technician if the supply is fine, as the outdoor board may need replacing.

A typical repair for this code costs $150–$800 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