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Error code reference

Friedrich Air Conditioner Error Code E3

Frost probe open

Friedrich codesFriedrich air conditioner codes

Frost probe open: normal operation is allowed.

First step from the service manual

Ohm frost probe. Replace probe if ohm value not read. If ohm value present, replace board.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E3 means on a Friedrich air conditioner

The E3 error code on a Friedrich air conditioner indicates that the frost probe circuit is open. The frost probe, also called the freeze sensor or anti-frost thermistor, monitors the evaporator coil temperature to prevent ice buildup during operation. An open circuit in this probe means the control board is receiving no signal from the sensor, which typically occurs when the probe's internal resistance element has failed or when the wiring between the probe and board has been severed or disconnected. Friedrich's control logic is designed to allow normal operation to continue even when this fault is present, so the unit will not shut down immediately.

The frost probe functions by changing resistance in response to temperature. The board reads this resistance value to determine coil conditions. When the circuit is open, no ohm value can be measured across the probe terminals, confirming the sensor element itself has failed. If an ohm reading is present when the probe is tested, the probe is electrically intact and the fault lies in the control board's ability to interpret that signal correctly, pointing to board replacement as the next step.

Diagnosis begins with isolating the probe using a multimeter set to resistance mode. Disconnect the probe from the board and measure across its terminals. A failed probe will show infinite resistance or no reading at all. A functioning probe will return a measurable ohm value consistent with its rated temperature response curve. If the probe tests good, the control board is the component responsible for the E3 fault and should be replaced.

Source: manufacturer service documentation.

Common causes of E3

  1. 01

    Failed frost probe sensor

    Part replacement

    The thermistor inside the frost probe has burned out or broken internally, creating an open circuit with no measurable resistance. This is the most likely cause and is confirmed when no ohm value can be read across the probe terminals.

  2. 02

    Broken or disconnected probe wiring

    Wiring / connection

    The wiring harness connecting the frost probe to the control board may have a break, loose connector, or corroded terminal that interrupts the circuit. Visually inspect the wire run and connector pins before condemning the probe itself.

  3. 03

    Faulty control board

    Part replacement

    If the frost probe tests good with a measurable ohm value, the control board's input circuit for the frost probe has failed. In this case the board must be replaced to clear the fault.

  4. 04

    Probe dislodged from mounting position

    Wiring / connection

    The frost probe is typically clipped or inserted near the evaporator coil and can work loose from physical vibration or during filter cleaning. A dislodged probe may produce erratic readings or no reading at all.

See the test procedure for each cause

Frequently asked questions about E3

What does E3 mean on a Friedrich air conditioner?
E3 on a Friedrich air conditioner means the frost probe circuit is open, indicating the control board is not receiving a resistance signal from the freeze sensor. The frost probe monitors the evaporator coil to prevent ice buildup. Friedrich's control logic allows the unit to continue operating normally while this code is active, but the underlying fault should still be diagnosed and repaired.
Will resetting the unit clear the E3 error code?
A simple power reset is unlikely to clear the E3 code permanently because it is triggered by a hardware fault in the frost probe circuit, not a temporary software condition. The code will return after reset if the probe is still open or the board input is still faulty. Proper repair requires testing the probe with a multimeter and replacing either the probe or the board based on the results.
Is it safe to keep running my Friedrich AC with an E3 code?
Friedrich's control system is designed to allow normal operation when E3 is active, so the unit is not in immediate danger of shutdown or damage from the error alone. However, without a functioning frost probe, the system loses its ability to detect ice buildup on the evaporator coil, which could allow freezing to go undetected over time. It is best to address the repair promptly rather than running the unit indefinitely with the sensor fault present.
How do I fix the E3 error on my Friedrich air conditioner?
Start by disconnecting the frost probe from the control board and testing it with a multimeter set to measure resistance. If the probe shows no ohm value, the probe has failed and should be replaced. If a resistance value is present, the probe is functional and the control board needs to be replaced. Both repairs require accessing internal components, so comfort with appliance disassembly or a qualified technician is recommended.
How much does it cost to repair an E3 error on a Friedrich air conditioner?
Repair costs depend on which component has failed. Frost probe sensors are generally inexpensive parts, with the probe itself typically ranging from $15 to $50 depending on the model. If the control board is at fault, board replacement is more involved and parts can range from $80 to $200 or more. Adding labor costs for a technician visit will increase the total, typically bringing the full repair into the $100 to $350 range depending on the diagnosis and your location.

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