We have a Trane TSC120E rooftop unit. Last fall, we heard some sort of loud noise in the ducts. We have been told by the maintenance company that the unit should never run during winter as it may freeze. They installed a thermostat so it shuts down whenever the temperature goes below 5C (41F), which means it doesn't run from november to april.

We ended up with severe negative pressure problems (building is very tight, Energy Star compliant). We're now being told by another company that it should run 24/7, 365 days per year.

Who's right? As it is our primary source of make-up air, I feel it should run throughout the year, but if it's not winter-proof, then I don't know what to do.

Any clues? Who's right -- is it meant to run throughout the year or should it be shut down during winter?