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Error code reference

Friedrich Air Conditioner Error Code E5

Indoor probe open

Friedrich codesFriedrich air conditioner codes

Indoor probe open: control assumes indoor ambient temperature is 90°F and unit will operate.

First step from the service manual

Ohm indoor probe. Replace probe if ohm value not read.

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

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What E5 means on a Friedrich air conditioner

The E5 error code on a Friedrich air conditioner indicates that the indoor ambient temperature probe has an open circuit condition. An open circuit in this context means the probe is no longer completing an electrical path that the control board can read, either due to a broken sensor element, a disconnected connector, or damaged wiring. Rather than shutting the unit down entirely, the Friedrich control board enters a failsafe mode, substituting a fixed assumed value of 90 degrees Fahrenheit for the missing sensor input and continuing to operate the unit based on that default.

The indoor probe is a thermistor, a resistive temperature sensor whose resistance changes predictably with temperature. The control board reads the probe's resistance value and converts it to a temperature reading used for cycle control and capacity decisions. When the board detects an open circuit (infinite or unmeasurably high resistance), it cannot determine actual room temperature and triggers E5. The primary diagnostic step is to disconnect the probe and measure its resistance with a multimeter. A healthy thermistor will return a readable ohm value; an open probe will show OL or infinite resistance, confirming the sensor has failed.

Common causes include a physically broken thermistor element, a connector that has worked loose from the control board or probe harness, or wiring that has been pinched, corroded, or damaged over time. Because the unit continues to run at the 90 degree assumption, cooling performance may be erratic or the unit may short-cycle, since actual room conditions are unknown to the control system. Prompt diagnosis and probe replacement restores accurate temperature sensing and normal operational control.

Source: manufacturer service documentation.

Common causes of E5

  1. 01

    Failed indoor thermistor (open element)

    Part replacement

    The thermistor sensor element itself has broken internally, creating an open circuit. This is confirmed by placing a multimeter across the probe terminals and reading infinite resistance or OL instead of a finite ohm value.

  2. 02

    Disconnected probe connector

    Wiring / connection

    The wiring connector attaching the probe to the control board or harness has worked loose. Inspect the connector at both the probe end and the board end for secure seating before replacing any parts.

  3. 03

    Damaged probe wiring

    Part replacement

    The wire leads running from the thermistor to the control board may be pinched, corroded, or broken, causing an open circuit in the harness rather than the sensor itself. Visually trace the wiring for signs of wear, pinch points, or corrosion at terminals.

  4. 04

    Corroded or oxidized connector terminals

    Wiring / connection

    Moisture exposure inside the unit can cause the connector pins or terminals to oxidize, increasing resistance to the point where the board reads the circuit as open. Cleaning the terminals may restore contact in mild cases.

  5. 05

    Control board fault

    Part replacement

    In rare cases, the input circuit on the control board that reads the probe may have failed, causing it to incorrectly interpret a functioning probe as open. This is only suspected after the probe and all wiring have been confirmed good with a meter.

See the test procedure for each cause

Frequently asked questions about E5

What does E5 mean on a Friedrich air conditioner?
E5 indicates the indoor ambient temperature probe has an open circuit and is not sending a readable signal to the control board. The control board responds by assuming a fixed indoor temperature of 90 degrees Fahrenheit and continuing to operate the unit. This failsafe allows the unit to keep running but without accurate temperature feedback, so cooling performance may be inconsistent. The probe should be tested with a multimeter and replaced if it does not return a readable resistance value.
Can I fix the E5 error code myself?
A knowledgeable DIYer can diagnose E5 by disconnecting the indoor probe and measuring its resistance with a multimeter. If the probe reads infinite resistance or OL, it needs to be replaced. Reconnecting a loose connector is also a straightforward fix. If the wiring or control board is involved, those repairs may require more technical comfort with appliance wiring.
Is it safe to keep running my Friedrich AC while E5 is displayed?
The unit will continue to operate using the 90 degree default assumption, so it is not in an immediate safety shutdown. However, running without accurate temperature sensing means the unit may not cycle correctly, potentially leading to inefficient operation or short-cycling. It is best to address the fault promptly rather than running the unit indefinitely in this condition.
Will resetting the unit clear the E5 error?
A power reset may temporarily clear the displayed code, but if the indoor probe is still open or disconnected, the E5 error will return once the control board attempts to read the sensor again. The underlying fault, whether a failed probe, loose connector, or damaged wire, must be corrected for the code to stay cleared.
How much does it cost to repair an E5 error on a Friedrich air conditioner?
If only the indoor thermistor probe needs replacement, parts typically cost in the range of $15 to $50 depending on the specific model. If a technician is needed for diagnosis and replacement, total repair costs including labor generally fall in the range of $75 to $200. Control board replacement, if required, would increase costs significantly beyond that range.

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