Either way, I'd say an aircon system is capable of changing temperature so quickly you're bound to be crossing the dew point multiple times in a day – I'd avoid this at all costs. a gentle background heater able to maintain a low temperature and another gentle/moderate heater for comfort when your actually in there seems to be a popular choice –
I still haven't sorted anything for my garage but I leave a dehumidifier on 24/7, it only turn on when humidity is over a certain level (about 60-70%) – nothings gone orange yet, but now the nights are getting rapidly colder I might just have to adjust the humidity stat to 50-60% – My lathe and my mill are wrapped in very heavy bath towels when not in use so they are less sensitive to changes in temperature and are still able to breath.
John, yes my car does to, it's very effective, even on the coldest mornings with a cold engine and frost screen – garage wise, so long as your air con drains the water outside rather than one of the floor standing "mobile" units that just recirculates it if you don't empty it out every few hours/days
Edited By Russ B on 06/10/2014 13:28:28