One possible answer, whether applies to some units but not others, no idea. Personally, I would pick up the telephone.
How does temperature affect ATP test result?
Ambient temperature of 20 – 22 degrees Celsius (70 – 72 degrees Fahrenheit) is the temperature that provides optimal performance. The only time ambient temperatures can affect results is if reagents are at a low temperature. This can happen if testing is done immediately after taking the tests out of the refrigerator. If testing in cold environments the SystemSURE Instrument will self-adjust to external temperature but the luciferase reagents needs to be at 20 – 22 degrees °C ( approx 70 degrees °F) to function at their best.
If reagents are cold, then the reaction will be slower and the RLU result for a given amount of ATP will be lower.
Temperature does not affect light measurement of the SystemSURE instrument provided that the instrument has equilibrated to the environmental conditions. The SystemSURE instrument will sense an environmental temperature change of 5 degrees °C and it will automatically initiate a 15 second recalibration sequence.
The user can also initiate a manual recalibration at any time by depressing and holding the OK button down for 3 seconds.
The system can be used in cold environments (e.g. 5 degrees °C) if the instrument is equilibrated for 10 – 15 minutes before use and that the reagent swab devices are kept warm e.g. by storage in an internal pocket close to body heat.