What do Danfoss Optyma Plus condensing unit alarm codes mean?
Part of the Danfoss walk-in controller codes hub. Same brand, different controller: Danfoss ERC 211 / 213 / 214, Danfoss EKC 202 / AK-CC 210.
Short answer: the Optyma Plus controller is mounted on the condensing unit — the outdoor or machine-room half of the system — so its alarms are about protecting the compressor and condenser: low suction pressure (A2), a high/low pressure safety trip (A17), a blocked condenser (A80), too-high discharge temperature (A96), a safety input (A97) or the speed drive (A98). E-codes are controller, sensor and pressure-transmitter faults. Danfoss's full list is below.
Which machines use it?
Danfoss Optyma Plus condensing units — the outdoor or machine-room half of many walk-in cooler and freezer installations — carry their own built-in electronic controller with a small display on the unit. It reports faults as short codes: A-codes for alarms (A2 low suction pressure, A17 pressure safety trip, A80 condenser airflow, A96 discharge temperature) and E-codes for controller defects. Because this controller lives on the condensing unit, its alarms lean toward compressor protection — pressure trips and overheating — rather than box temperature. Practical tip: when one of these codes stops the compressor, resist the urge to keep resetting; the protections exist because forcing restarts is how compressors get destroyed.
How do you read and clear the display?
When there's an error the LEDs on the front flash and the alarm relay switches on; push the top button to see the alarm report. E-alarms show the moment the error occurs; A-alarms only once their time delay has passed, and an A-alarm stays hidden while an E-alarm is active.
How do you enter the parameter menu?
The Optyma Plus controller shares the Danfoss three-button layout. From the user guide:
- Hold the upper button for a couple of seconds until parameter r05 is shown.
- Press upper or lower to find the parameter you want to change.
- Hold the middle button until the value is shown.
- Press upper or lower to select the new value.
- Press the middle button again to freeze the value.
Leave it alone for 20 seconds (5 on some settings) and the display drops back to the Ts/Tc temperature readout on its own.
The one thing to be careful with: the condensing-temperature reference — the set point the fan control works to — is shown with a brief push of the middle button and adjusted with the upper and lower buttons without entering the parameter menu. The guide warns that care is needed not to adjust it unintentionally, and a nudged reference is a plausible cause of a unit that suddenly runs its fans differently or trips head-pressure alarms in warm weather.
Danfoss's quick-start sequence for a new controller: open r12 and stop regulation, select the refrigerant in o30, then set r12 back to start (with start/stop on DI1 or DI2 also active). The controller ships preset to its condensing-unit type in o61; if the refrigerant you pick isn't permitted for that unit the display shows ref and waits for a new entry.
Every Danfoss Optyma Plus code at a glance
| Code | What it means |
|---|---|
| A2 | LP alarm — low suction pressure |
| A11 | No refrigerant selected — set parameter o30 |
| A16 | DI2 alarm — check the function that sends a signal to the DI2 input |
| A17 | HP alarm — high/low pressure safety trip |
| A45 | Standby mode |
| A80 | Condenser blocked — airflow decreased |
| A96 | Maximum discharge temperature exceeded |
| A97 | Safety alarm — a safety function on DI2 or DI3 is activated; check that input and the compressor's direction of rotation |
| A98 | Drive alarm — alarm from the speed regulation; check the speed regulation |
| E1 | Controller fault |
| E20 | Error on pressure transmitter Pc (condensing pressure) |
| E30 | Error on the aux sensor (S5) |
| E31 | Error on the air (ambient) sensor S2 |
| E32 | Error on the discharge sensor S3 |
| E33 | Error on the suction gas sensor S4 |
| E39 | Error on pressure transmitter Ps (suction pressure) |
6 codes link to a full section below. The other 10 are listed as the manufacturer's manual gives them. Every row comes from the manual cited at the end of this page.
What does each code mean — and what should you do?
A2 — LP alarm — low suction pressure
Suction pressure is too low. The controller stops the compressor for protection. Common field causes include low refrigerant charge or an iced/starved evaporator, which are technician territory.
What causes it:
- Suction pressure below the safe limit — the controller stops the compressor to protect it
- Low refrigerant charge
- An iced or starved evaporator — heavy coil ice, dead evaporator fans, or product blocking airflow
Can staff fix it? Only the airflow part: check the evaporator for heavy ice and confirm the fans run and product isn't blocking them. Do not repeatedly reset the alarm — that short-cycles the compressor.
What to check, in order:
- Check the evaporator inside the box for heavy ice buildup
- Confirm evaporator fans are running and airflow isn't blocked by product
- Do not repeatedly reset the alarm — that short-cycles the compressor
- Monitor box temperature and move product if cooling has stopped
Why it takes a technician: Low-pressure trips usually mean a refrigerant or airflow problem that takes gauges and EPA Section 608 certification to diagnose — and with the compressor stopped, product loss is on the clock.
Source: Danfoss — Controller for condensing unit Optyma Plus, SW 3.7x — user guide (BC172686425380en-001202)
A17 — HP alarm — high/low pressure safety trip
The high-pressure (or combined high/low pressure) safety input has tripped. The controller stops the compressor. High-pressure trips are very often a dirty or blocked condenser.
What causes it:
- The high-pressure (or combined high/low pressure) safety input tripped and the controller stopped the compressor
- Very often a dirty or blocked condenser that can't reject heat
- A condenser fan that isn't running
- Material stacked around the condensing unit choking its airflow
Can staff fix it? The most common cause is: with power off at the breaker, brush or vacuum the coil face, clear everything around the unit, confirm the fan runs. Restore power once and monitor — do not keep resetting a pressure trip.
What to check, in order:
- Check the condenser coil for dirt, lint, or blockage and confirm the condenser fan runs
- Clear anything stacked around the condensing unit that restricts airflow
- With power off at the breaker, brush or vacuum the coil face clean
- Restore power once and monitor — do not keep resetting a pressure trip
Why it takes a technician: Repeated high-pressure trips damage the compressor, and forcing restarts against a pressure safety is how condensing units die. If it trips again after a cleaning, the refrigerant side needs certified diagnosis immediately — the box isn't cooling while the compressor is locked out.
Source: Danfoss — Controller for condensing unit Optyma Plus, SW 3.7x — user guide (BC172686425380en-001202)
A45 — Standby mode
The condensing unit is in standby — refrigeration was stopped via the r12 main switch or the DI1 input, not by a fault. The manual notes r12 and/or the DI1 input will restart regulation.
What causes it:
- Refrigeration stopped via the r12 main switch — deliberate standby, not a fault
- The DI1 input (an external switch) stopped the unit; per the manual, r12 and/or DI1 restart regulation
Can staff fix it? Yes, if someone shut it down on purpose — check with staff, check any external switch wired to DI1, and verify box temperature since the unit hasn't been cooling.
What to check, in order:
- Check whether someone deliberately shut the unit down
- Check any external switch wired to DI1
- Verify box temperature and move product if the unit has been off
Why it takes a technician: If nobody stopped it, the r12 setting or DI1 wiring has to be checked inside the controller's configuration — guesswork there keeps the condensing unit off and the box warming.
Source: Danfoss — Controller for condensing unit Optyma Plus, SW 3.7x — user guide (BC172686425380en-001202)
A80 — Condenser blocked — airflow decreased
The controller has detected reduced airflow through the condenser. The manual's stated action is to clean the condensing unit.
What causes it:
- Airflow through the condenser has dropped — the manual's stated action is to clean the condensing unit
- Leaves, lint, dust, or debris matted on the coil
- Space around the unit blocked so it can't breathe
- A condenser fan not spinning freely
Can staff fix it? Yes — this is the alarm the manual tells you to fix with a cleaning. Power off at the breaker, remove debris from the coil, clear the space around the unit, check the fan spins freely, restore power, and confirm the alarm clears.
What to check, in order:
- Turn the unit off at the breaker
- Remove leaves, lint, dust, and debris from the condenser coil and clear space around the unit
- Check that the condenser fan spins freely
- Restore power and confirm the alarm clears
Why it takes a technician: If A80 comes back after a thorough cleaning, the fan motor or system pressures are at fault — live motor testing and gauge work, and a condenser that can't reject heat is steadily overworking the compressor.
Source: Danfoss — Controller for condensing unit Optyma Plus, SW 3.7x — user guide (BC172686425380en-001202)
A96 — Maximum discharge temperature exceeded
The compressor discharge gas temperature has exceeded its limit and the controller protects the compressor. Often related to condenser airflow or refrigerant-side problems.
What causes it:
- Compressor discharge gas temperature over its limit — the controller steps in to protect the compressor
- Blocked or dirty condenser airflow
- The unit enclosed in a hot, unventilated space
- Refrigerant-side problems driving discharge temperature up
Can staff fix it? Only the airflow checks: clean visible dirt off the condenser (power off first) and make sure the unit isn't boxed into a hot corner. Avoid repeated resets.
What to check, in order:
- Check the condenser for blocked airflow and clean visible dirt (power off first)
- Make sure the unit isn't enclosed in a hot, unventilated space
- Monitor box temperature and avoid repeated resets
Why it takes a technician: Overheating discharge gas destroys compressors if the root cause isn't fixed — the refrigerant-side diagnosis behind it is gauge work for an EPA Section 608-certified tech, not something to reset past.
Source: Danfoss — Controller for condensing unit Optyma Plus, SW 3.7x — user guide (BC172686425380en-001202)
E1 — Controller fault
Internal fault in the Optyma Plus controller itself ('Ctrl. Error'). This is an electronics problem, not an operating condition.
What causes it:
- An internal fault in the Optyma Plus controller's own electronics ('Ctrl. Error')
- Not an operating condition — the control hardware itself is the problem
Can staff fix it? One power cycle at the breaker for a few minutes. If E1 returns, record it and watch box temperature — there is no further staff step.
What to check, in order:
- Power-cycle the unit at the breaker for 2-3 minutes
- If the code returns, record it and monitor box temperature
- Move product if the unit stops holding temperature
Why it takes a technician: A persistent controller fault means professional testing or replacement of the control board — live electrical work on the condensing unit — and until then the unit's protections and regulation can't be trusted.
Source: Danfoss — Controller for condensing unit Optyma Plus, SW 3.7x — user guide (BC172686425380en-001202)
How do you diagnose a Danfoss Optyma Plus alarm, step by step?
- Push the top button and read the report. Note every code before resetting anything.
- A45 isn't a failure. Standby means refrigeration was stopped via parameter r12 or the DI1 input; r12 and/or DI1 start it again.
- A80 is the one you can act on. Airflow across the condenser has decreased, and Danfoss's action is simply: clean the condensing unit. The alarm is raised when condensing temperature stays too high — limit set by A70 — for the delay set by A71.
- A2, A17 and A96 are protections — don't keep resetting them. Danfoss's instruction for all three is to follow the condensing unit's own instructions. The controller counts high- and low-pressure trips (read-outs P51 and P52): a climbing count points at a system problem, not a one-off.
- Discharge temperature is handled in stages. If the discharge temperature (sensor Td) gets too high, the controller first reduces compressor capacity and runs the condenser fan at 100 %; if that doesn't bring it down it stops the compressor and raises A96, reconnecting the compressor once the temperature is 10 K below the limit.
- Sensor and transmitter errors (E20, E30–E33, E39): check the sensor and its connection.
- A11 means no refrigerant type has been selected — parameter o30 has to be set.
Which parts are usually involved?
| Part | Codes that point to it | Note |
|---|---|---|
| Suction pressure transmitter Ps | E39, A2 | |
| Condensing pressure transmitter Pc | E20 | |
| High / low pressure safety switch (DI3) | A17 | |
| Discharge temperature sensor Td (S3) | E32, A96 | |
| Suction gas sensor S4 | E33 | |
| Ambient air sensor S2 | E31 | |
| Condenser coil and fan | A80 | |
| Compressor speed drive | A98 | |
| Safety devices on DI2 / DI3 | A97, A16 |
What refrigeration is behind these codes?
Every code here is the controller reporting a reading from the refrigeration system. The background is explained once, for every controller on this site: why the condenser matters; what superheat is and why controllers alarm on it; refrigerants and the A2L change.
The compressor itself — how it works and why these protections exist — is general compressor theory, which our sister site aircompressorcodes.com covers. This page stays with what the Optyma Plus controller reports.
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 walk-in coolers — real businesses with verified contact information, none of whom paid to be listed.