Why did motor overload relay F21 trip on my Atlas Copco?
Short answer: Main motor overload — compressor does not start or stops. If your Atlas Copco GA 30+-90 / GA 37+ (Elektronikon Touch) is showing Motor overload relay (F21) open, the controller has logged a specific, documented condition. This page covers what it means, what causes it, what you can safely fix yourself, and when — and why — it takes a technician.
What exactly is the machine telling you?
The drive motor's overload relay F21 has opened, so the compressor will not start or has stopped during operation. The instruction book's remedy is to find the cause, remedy it, and replace the relay if necessary.
Which machines show this?
Atlas Copco's current-generation GA 30+ through GA 90 oil-injected rotary screws — the '+' models such as the GA 37+ — carrying the Elektronikon Touch controller with its color touchscreen. These are the newest machines in the GA line, and their instruction books lean on documented cause lists (oil level, cooling air, relay designations like F21, Q15, F15, K25) rather than bare code numbers, so faults often read as plain-language conditions. Practical tip: the manual warns that pressing the emergency stop does not make the compressor voltage-free — any electrical-cabinet check on these machines starts with switching off and locking out the supply, full stop.
What causes it?
- Motor working too hard: blocked cooling air, very high ambient, or a discharge pressure setpoint set too high
- Overload relay F21 opened and hasn't cooled yet
- An underlying motor or starter fault if the trip repeats
Can you fix it yourself?
Rarely beyond the basics — staff can clear blocked cooling air, sanity-check the pressure setpoint, and let things cool. A repeat trip is not something to keep resetting.
Step by step — what to try, in order:
- Switch off and lock out the voltage — the manual warns that pressing the emergency stop alone does not make the compressor voltage-free
- Check for obvious causes of high load: blocked cooling air, very high ambient temperature, high discharge pressure setpoint
- Let the motor and relay cool before any reset attempt
- Log the trip time and conditions for the service technician
When do you need a technician — and why?
Measuring phase currents and inspecting the motor and starter means opening a live-capable electrical cabinet under lockout — the manual itself warns the E-stop alone does not make the machine voltage-free.
If it does come to a service call and you're in Nashville, TN or Birmingham, AL, we maintain independently compiled lists of local companies that service industrial air compressors — real businesses with verified contact information, none of whom paid to be listed.
Related questions
What does Motor overload relay (F21) open mean on an Atlas Copco GA 30+-90 / GA 37+ (Elektronikon Touch)?
Main motor overload — compressor does not start or stops. The drive motor's overload relay F21 has opened, so the compressor will not start or has stopped during operation. The instruction book's remedy is to find the cause, remedy it, and replace the relay if necessary.
Can I fix Motor overload relay (F21) open on an Atlas Copco GA 30+-90 / GA 37+ (Elektronikon Touch) myself?
Rarely beyond the basics — staff can clear blocked cooling air, sanity-check the pressure setpoint, and let things cool. A repeat trip is not something to keep resetting.
When does Motor overload relay (F21) open on an Atlas Copco GA 30+-90 / GA 37+ (Elektronikon Touch) need a technician?
Measuring phase currents and inspecting the motor and starter means opening a live-capable electrical cabinet under lockout — the manual itself warns the E-stop alone does not make the machine voltage-free. Any repeated motor-overload trip needs an electrician or Atlas Copco technician to measure phase currents and inspect the motor and starter.
Verified against service documentation: Atlas Copco GA 30+-90 / GA 37+ (Elektronikon Touch) documentation for Motor overload relay (F21) open (manualslib.com)