What causes York Mini Split E4?

Low refrigerant from a leak in the system piping. With too little charge the compressor runs hot, and York's M series flowchart sends a real high discharge temperature straight to finding the leak and charging to the nameplate amount. A restriction or a problem with the electronic expansion valve (EEV). York's P series overload and exhaust diagnosis checks that the expansion valve is connected and not damaged before looking at the board. A faulty or misplaced discharge (exhaust) temperature sensor that reads hot when the compressor isn't. The M series flowchart says to replace the sensor if its resistance is wrong. A failed outdoor control board, if the actual discharge temperature is normal and the sensor tests good. Hard running conditions, such as a dirty outdoor coil or indoor filter, or very high outdoor temperatures, can push discharge temperature up too. That's general HVAC guidance rather than a step in York's E4 chart.

How do I fix York Mini Split E4?

Turn the system off with the remote. On M series multi-zone units, if it has locked out after repeated trips, switch the outdoor unit's breaker or disconnect off for a few minutes and back on. Clean or replace the indoor unit's filters and make sure the indoor unit's air intake and outlet aren't blocked. With power off at the outdoor disconnect, clear leaves, grass or stored items from around the outdoor unit and gently rinse a dirty outdoor coil with a garden hose (no pressure washer). Look for oily spots on the refrigerant line connections at the indoor and outdoor units, which can point to a leak. Don't loosen any fittings yourself. If E4 comes back, stop resetting it and call a technician. Running a compressor that keeps overheating can damage it.

When should I call a pro for York Mini Split E4?

A technician measures the actual compressor discharge temperature. York's M series flowchart uses 115 C (239 F) as the line: at or above it, the system has a leak and needs repair and recharge to the nameplate amount. If the discharge temperature isn't really that high, the discharge temperature sensor's resistance is checked against York's resistance table and the sensor is replaced if it's off; if the sensor is fine, the outdoor mainboard is replaced. On P series units, York's diagnosis has the technician wait 20 minutes after powering off, then check the electronic expansion valve's connection and coil resistance (the first four pins to the fifth should be about equal and under 100 ohms), replace the valve or the outdoor control board, and then look for a refrigerant leak. Leak repair and recharging must be done by an EPA-certified technician.

Code: E4🔧 York Mini Split

York Mini Split Error Code E4: High Discharge Temperature Protection (Meaning, Causes, Fixes)

Q: What does York Mini Split E4 mean?

E4 on a York ductless mini split means compressor discharge (exhaust) high temperature protection: the outdoor unit's discharge temperature sensor read the hot gas leaving the compressor as too hot, so the compressor slowed down and then stopped to protect itself. York's service flowchart points first at a refrigerant leak (low charge makes the compressor run hot), then at a faulty discharge temperature sensor, and last at the outdoor control board. On York M series multi-zone units, after six protection stops in a row the compressor won't restart until the outdoor unit's power is cut and restored. York (Johnson Controls) uses E4 for compressor discharge temperature protection on its ductless mini splits. The M series multi-zone service manual (outdoor models DHM18CMB21S through DHM42CMB21S, on yorknow.com) lists E4 as High Discharge Temp Protection, an outdoor-unit error shown on the indoor display and the outdoor unit's display, with the indicator flashing 4 times. Its control description says that as discharge temperature rises the compressor first limits or lowers its speed, and when it gets too high the compressor stops; if discharge temperature protection happens 6 times in a row, the compressor can't resume until the power is cut off and switched back on (the count clears once the compressor runs longer than 7 minutes). Its E4 flowchart checks whether the discharge temperature has actually reached 115 C (239 F). The York P series 9K-12K 115 V single-zone service manual also lists E4 as Compressor exhaust high temperature protection, with 4 blinks on the indoor lamp. Related codes on the same units: F5 is a failed (open or shorted) exhaust temperature sensor, F9 on the P series is the earlier high exhaust temperature speed limit, E1 is high pressure protection and E3 is low pressure protection.

Reviewed 2026-10-25 · Based on 2 manufacturer & service sources

What the code means

York (Johnson Controls) uses E4 for compressor discharge temperature protection on its ductless mini splits. The M series multi-zone service manual (outdoor models DHM18CMB21S through DHM42CMB21S, on yorknow.com) lists E4 as High Discharge Temp Protection, an outdoor-unit error shown on the indoor display and the outdoor unit's display, with the indicator flashing 4 times. Its control description says that as discharge temperature rises the compressor first limits or lowers its speed, and when it gets too high the compressor stops; if discharge temperature protection happens 6 times in a row, the compressor can't resume until the power is cut off and switched back on (the count clears once the compressor runs longer than 7 minutes). Its E4 flowchart checks whether the discharge temperature has actually reached 115 C (239 F). The York P series 9K-12K 115 V single-zone service manual also lists E4 as Compressor exhaust high temperature protection, with 4 blinks on the indoor lamp. Related codes on the same units: F5 is a failed (open or shorted) exhaust temperature sensor, F9 on the P series is the earlier high exhaust temperature speed limit, E1 is high pressure protection and E3 is low pressure protection.

Likely causes

Low refrigerant from a leak in the system piping. With too little charge the compressor runs hot, and York's M series flowchart sends a real high discharge temperature straight to finding the leak and charging to the nameplate amount.
A restriction or a problem with the electronic expansion valve (EEV). York's P series overload and exhaust diagnosis checks that the expansion valve is connected and not damaged before looking at the board.
A faulty or misplaced discharge (exhaust) temperature sensor that reads hot when the compressor isn't. The M series flowchart says to replace the sensor if its resistance is wrong.
A failed outdoor control board, if the actual discharge temperature is normal and the sensor tests good.
Hard running conditions, such as a dirty outdoor coil or indoor filter, or very high outdoor temperatures, can push discharge temperature up too. That's general HVAC guidance rather than a step in York's E4 chart.

Safe DIY checks

⚠ Before you start

The outdoor unit has line voltage and an inverter board that can stay charged after power is removed (York's P series procedure waits 20 minutes), and the compressor's discharge line can be hot enough to burn. Shut off power at the disconnect before cleaning the outdoor unit, keep the electrical covers on and leave sensor, valve and refrigerant work to a licensed technician.

Turn the system off with the remote. On M series multi-zone units, if it has locked out after repeated trips, switch the outdoor unit's breaker or disconnect off for a few minutes and back on.
Clean or replace the indoor unit's filters and make sure the indoor unit's air intake and outlet aren't blocked.
With power off at the outdoor disconnect, clear leaves, grass or stored items from around the outdoor unit and gently rinse a dirty outdoor coil with a garden hose (no pressure washer).
Look for oily spots on the refrigerant line connections at the indoor and outdoor units, which can point to a leak. Don't loosen any fittings yourself.
If E4 comes back, stop resetting it and call a technician. Running a compressor that keeps overheating can damage it.

🛠 When to call a pro

A technician measures the actual compressor discharge temperature. York's M series flowchart uses 115 C (239 F) as the line: at or above it, the system has a leak and needs repair and recharge to the nameplate amount.
If the discharge temperature isn't really that high, the discharge temperature sensor's resistance is checked against York's resistance table and the sensor is replaced if it's off; if the sensor is fine, the outdoor mainboard is replaced.
On P series units, York's diagnosis has the technician wait 20 minutes after powering off, then check the electronic expansion valve's connection and coil resistance (the first four pins to the fifth should be about equal and under 100 ohms), replace the valve or the outdoor control board, and then look for a refrigerant leak.
Leak repair and recharging must be done by an EPA-certified technician.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Refrigerant leak detector

For a technician tracking down the leak York's E4 flowchart points to.

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⚙

Coil cleaner

For cleaning a dirty outdoor coil with the power off.

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⚙

Multimeter

For checking the discharge temperature sensor's resistance against York's table.

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Sources

Last reviewed 2026-10-25. Always confirm against the manual for your exact model number.