Re: New Carrier Infinity System. The Carrier guys who installed our system said there should never be any water in the drip pan. A month later I have about a 1/4 inch of water. They've come out once for this and taped everything - said it was condensation on the drain line. Can't find the source this time - maybe coming from the evaporator coil? Should I call them back out? Should I be concerned?
If you're speaking about the secondary drip pan located underneath the air handler, then yes, it should be dry if everything is draining correctly and unit is level or pitched slightly so the evaporator drain pan can drain properly.
If cooling coil is on the negative (intake) side of the blower, as in a heat pump, the primary drain line should be trapped (with vent downstream of the trap) to allow the trap to form a water seal so the drain pan can drain properly.
Also, if your secondary drain pan does not have its own drain line to the outdoors (preferably over a kitchen window so you'll know when the primary is clogged and the secondary is draining), there should be a float switch (which will stop the cooling and further creation of condensate) in the drain pan to prevent the water from reaching disastrous levels, overflowing the pan, and damaging your house.
I definitely would have the installer return to resolve this problem. Don't let it go.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
If the pan is of metal construction, it won't last long if it continues to see water. Whether plastic, or metal there should not be 1/4" of water in it on a constant basis. A few drops maybe, but more than that would indicate a problem.
There is nothing more frightful than ignorance in action....Mark Twain