[DangeloInspections]

Gracie,
This is typically caused by either a leaking water tank, (but most likely NOT, because you should have a drain pan plumbed out to the exterior to prevent this), or more than likely this is caused from your A/C unit.

Under your A-coil, you have a drain pan inside your A/C air handler. This is right above your filter. If you take your filter out you should see the plastic drain pan surrounding the air handler cabinet.

When everything is perfect, the condensate water goes into this drain pan, and goes out your condensate line all the way outside.

It sounds like you have condensate water slowly dripping in and around your air handler, which in time can swell, rot, and deform that wood platform. This is bad, as that wood platform supports your air handler and helps support your over 700 pound hot water heater. There are 2-3 reasons how this can happen.

This line should be kept clear, usually by pouring a half gallon of hot water down it a few times a year. If this gets clogged, the water can back up and overflow onto and into and around the air handler cabinet and the wood platform below.

On the newer air handlers, there is a float switch installed that shuts off your A/C until you blow out this clogged pipe. Your older A/C unit may not have this safety switch. It is a good thing to have. They are not costly.

If the line is clear, you MAY have a cracked drain pan, thus allowing the water to leak.

Lastly, you may also have excessive sweating from a poorly insulated lineset. Are there rust spots on the air handler? Staining from sitting water on the platform?

If the deflection is not too bad, you may be able to shore the platform up and fix the problem. If is is too far gone, that platform top may need replacing. This may be costly, as the air handler and perhaps your water heater would need to be raised a bit, temporarily supported and a new piece of plywood installed.

Also, take your a/c filter out and check below for wetness. Also check your filter for wetness. If wet, this may cause mold issues in the bottom portion of the return.

I'm sorry that I am not giving you good news, but I hope this helps. I would check for condensate leakage in and around the A/C air handler as soon as possible.

Frank