Winter is when air handling units fail, and it is rarely a coincidence. Cold weather puts specific stresses on an AHU that the rest of the year does not, and a unit that has coasted through summer can be caught out by the first hard frost. A little preparation avoids a mid-winter breakdown when you can least afford one.
Why frost is a problem
The vulnerable component is the heating or cooling coil. Coils carry water, and water freezes. When very cold outdoor air passes over a coil — particularly if flow through the coil is low or has stopped — the water inside can freeze, expand and split the coil. A burst coil is not a small repair: it means a shutdown, water damage, and a significant bill, often at the worst possible time of year.
Heat recovery components and condensate systems are also at risk. Condensate that cannot drain freely can freeze and block, and heat exchangers can ice up if not managed.
What frost protection does
Frost protection is a set of controls and safeguards that stop the unit reaching the point of damage. A frost thermostat monitors temperature at the coil and takes action as it approaches freezing — closing the fresh air damper, bringing on the heating, or shutting the unit down safely to protect it. Correctly set up, it means the AHU protects itself before a coil is at risk.
The problem is that frost protection is often either not fitted, not set correctly, or has quietly failed — and nobody notices until the coil bursts. It is a classic case of a safeguard that only proves itself the day it is needed.
Getting winter-ready
A pre-winter check should confirm that frost protection is present and working, that frost thermostats are set to the right temperature, that dampers close fully and promptly on demand, that condensate drainage is clear and protected, and that the heating side of the unit is actually delivering. It is also the moment to catch the general wear — worn belts, tired bearings, dirty coils — that cold-weather demand tends to expose.
None of this is complicated, but it has to be done before the cold arrives, not after the coil has split.
We carry out pre-winter checks and frost protection servicing as part of AHU maintenance, so your units go into winter ready rather than exposed. If you have never had frost protection verified, do it before the temperature drops.
