The furnace is leaking water when the air conditioning is on... rheem 90plus edition

I presume you're talking about a gas furnace, even tho the title says Rheem gas water heater. Either way, it works the same for both.

Any black coloring on the heat exchanger is *not* from overheating. Black is from a sooty flame caused by a mis-adjusted burner. (In fact, a sooty flame is less hot). There is an adjustable "air intake plate" for air to enter the burner where the gas enters the burner. A proper flame is made by adjusting this air opening so the proper gas/air mixture feeds into the burner. If the air vent is closed too much it produces a sooty flame.
The age of the furnace is the most important aspect, and that helpful to determine a likely condition of the heat exchanger and burners. Other than a badly adjusted flame, the main thing to watch for is a badly rusted out heat exchanger. But black does not mean rust.

Check condensate water /drain stopped up. It will allow a start after a reset but then it shuts the combustion air fan down and that shuts the unit down this will require a service tech make sure their familiar
with 95% units

Hi,

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Have you checked to make sure that all of the supply registers are open, the air filter is clean and nothing is blocking the return air grill?
It almost sounds like you could be cycling on a limit switch.
Usually on gas furnaces, the blower is controled by the onboard controls, in the cooling mode the thermostat will control the blower.
I would be looking past the thermostat, at the furnace it self.
I hope you find this helpful. If you continue to experience problems, please let us know and we will dig deeper. :)
Paul

Maybe some trash or water got into the hose from the draft inducer to the proving switch It happens this time of year.

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What is the make and model #?

Your furnace is going into a lockout condition, cycling the power resets the circuit board and it starts over. I will need to know approximate age and model of your furnace, it sounds like you have need to clean the flame sensor rod. However i need to know what i am working with.

This is not a lot to go on.

I assume since you called it a furnace, you have hot air heat and central air conditioning. If so, the only way a furnace/AC unit can generate water is by condensing moisture from the air. This is common to all air conditioning and removes humidity from your home. If so, this water, called condensate, must drain. The condensate is collected at the AC cooling coil that is typically located on top of a vertical upflow furnace or downstream of a horizontal furnace. If the drain is clogged, it will overflow and create a mess in and around the furnace. If this is your problem, cleaning and clearing debris may solve the issue. I suggest starting with the easiest accessable part of the drain path. You may need to open the panels enclosing the AC coil and clean the small pans at the bottom of the coil and clear openings from above that look similar to a laundry tub drain. If you get that far and find rust holes in the pan, repairs are needed. If you have an electric condensate pump that may also be the cuprit and require cleaning. Check and clear all drain lines from the coil connection to the final dicharge - sump pit or outside.

the air flow you feel coming out of the vents is good on heat but not when the ac is running?

The thermostat activates the y command. The wiring passes through the furnace, but the furnace does not activate the compressor.