I've been told by a knowledgeable engineer that when a glycol solution freezes, the water freezes first and increases the glycol concentration. It stands to reason this is true since a glycol solution is a mixture. I've seen a glycol solution with a 13F freezepoint that had ice crystals floating in it.
So, if a refrigerant-to-water heat exchanger is chilling a glycol solution to 25F and the evaporator temp is 0F and the glycol freeze point is 10F, wouldn't a pure water ice form on the evaporator? And if pure water ice forms on the evaporator, wouldn't the glycol solution have to reach 32F+ to thaw the ice?