Areas that have experienced flooding from Sandy have a big cleanup job and lots of rebuilding ahead. Make sure your students know to be careful when working on equipment that may have been flooded. Even after drying out, the corrosion and debris left behind can make the controls and motors inoperable. Worse, they can be dangerous. While it is possible that many parts of the system may still function properly, it is really a gamble to operate equipment that has been flooded. Safety controls that have been under water cannot be relied on to work. Silt and debris can create potential shorts or prevent proper mechanical operation. This can turn a normal malfunction into a potentially dangerous situation. For example: a blower motor on a furnace starts, but fails after a few hours of operation. The limit does not shut off the burners because its contacts are shorted together, the furnace overheats and burns the house down.
Another concern is for the health of the building occupants. Flood waters contain all types of things that you really don’t want in your air conditioning system: chemicals, gasoline, dead animals, and sewage to name a few. Coils , equipment cabinets, and insulation will all retain some of these undesirable things even after the water has receded. Technicians may be asked to repair flood damaged equipment, but in most cases the proper repair is more costly than replacing the equipment. It is hard to tell someone who has just lost most of their possessions that you cannot fix their flood damaged equipment, but that is exactly what you should do. Then there is the matter of duct work: obviously a good place to catch things. Again, cleaning may not really be practical.
A danger to technicians working in a previously flooded area is the muck they will often be working in. They will be walking, crouching, crawling, sitting, and laying on this muck when they go in the house to look at the equipment. Again, this is not just mud. This is a combination of nasty stuff that is definitely hazardous to your health. For more information on flood damaged equipment check out the AHRI page on flooded equipment.