MRCOOL air conditioner EC error code: refrigerant leak or low refrigerant detected

What the EC code means

EC on a MRCOOL mini-split means the system has detected a refrigerant leak or low charge. Gen 4 and Gen 5 units show it as EL 0C. On a new DIY install, MRCOOL says a loose line-set connection or a service valve that is not fully open is the usual cause.

The system watches how cold the indoor coil gets once the compressor runs. If the coil does not cool as expected, it assumes refrigerant is missing and stops to protect the compressor.

MRCOOL DIY units come pre-charged and use quick-connect line sets, so a leak on a new install is usually at a connection you can check yourself. On a system that has run for a while, EC almost always means a real leak that needs a technician.

Common causes

Listed from most to least common.

1. Line-set connection not fully tightened, with threads still showing
2. Allen key service valves on the outdoor unit not fully opened
3. Refrigerant leak at a connection, coil or line set on an older system
4. Kinked line set restricting refrigerant flow
5. Indoor pipe temperature sensor loose, out of place or faulty (rare)

How to fix the EC code

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

1. 1

   Step 1: Turn the system off

   Switch the unit off with the remote and turn off the breaker before you check connections.

2. 2

   Step 2: Check the service valves

   On the outdoor unit, remove the valve caps and check that both Allen key valves are opened all the way. MRCOOL says a closed or half-open valve traps refrigerant in the condenser and causes this code.

3. 3

   Step 3: Check the line-set connections

   Look at every connection on the condenser, the air handler and any extension couplers. MRCOOL says no threads should be visible. If you can see threads, hold the adapter steady with one wrench and tighten the line-set nut with a second wrench.

4. 4

   Step 4: Look for oily spots

   Oily residue on a fitting, the line set or its insulation often marks where refrigerant has leaked. Note where you see it.

5. 5

   Step 5: Restart and test

   Turn the power back on and run the system. If EC returns, stop using it and book a technician.

You'll need: Allen key (hex) wrench set, two adjustable wrenches, flashlight.

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

If EC returns with the valves open and the connections tight, the system has lost refrigerant. A licensed HVAC technician must find and fix the leak, pull a vacuum and recharge it. In the US, handling refrigerant requires EPA certification, so never add refrigerant yourself.

A typical repair for this code costs $300–$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