E4
Carrier Split AC
Severity: ModerateWhat Does This Error Mean?
E4 on a Carrier AC means the indoor evaporator coil temperature has dropped to an abnormally low level — the coil is at risk of freezing or has already begun to ice up. Carrier stops cooling to allow the coil to defrost and prevent ice from blocking airflow entirely. A dirty air filter is the most common cause.
Affected Models
- Carrier Ester Series
- Carrier Flexicool Series
- Carrier Cyclojet Series
- Carrier Inverter Split AC (all models)
Common Causes
- Air filter clogged — restricted airflow causes the coil to overcool and freeze
- Blower fan running too slow or motor failing — insufficient airflow over the evaporator
- Low refrigerant — pressure drops too low causing the evaporator to run very cold
- Room temperature set too low with a very small room — coil overcools quickly
- Indoor coil evaporator thermistor faulty — false low temperature reading
How to Fix It
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Turn off the AC and switch to fan-only mode for 30-60 minutes.
Do not turn the AC off completely if ice has formed — fan-only mode helps melt the ice faster. Alternatively, turn off completely and allow natural defrost with the unit open.
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Clean or replace the indoor air filter.
Remove the front panel, slide out the filters, and wash them under running water. Allow to dry fully before reinstalling. A blocked filter is the cause of E4 in the majority of cases.
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Check that all supply vents are open and not blocked.
Closing too many room vents restricts return airflow to the indoor unit. All vents should be open when the AC is running.
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If E4 returns after filter cleaning, call a Carrier technician.
Low refrigerant or a blower motor fault requires professional diagnosis.
Frequently Asked Questions
How often should I clean the Carrier AC filter to prevent E4?
Carrier recommends cleaning the indoor air filter every 2 weeks during periods of heavy use, and at least once a month otherwise. In dusty environments or homes with pets, clean every 1-2 weeks without exception. A clean filter is the single most important maintenance task for any split AC.
Can E4 cause water to drip from the indoor unit?
Yes. When ice forms on the evaporator coil and then melts, the drainage system can be overwhelmed and water may drip from the indoor unit. Place a towel under the indoor unit when defrosting after E4. Once the ice is fully melted and E4 is resolved, the dripping should stop.