PROBLEM:
There is a continuous drain (24/7)which discharges through one of two pvc drain pipes at the rear of the garage. One Pipe discharges when the A/C is on; the other when the system is on or off.

QUESTION:
What's causing this continuous flow and what can be done to stop it, if any?

BACDGROUND:
There is what I beleive to be a part of the a/c unit in my garage attic. It's large box with bellow attached, which could be the ventalation unit. Then, there is a Rheem a/c unit behind garage. finally, there is the Rheem gas furnace in the garage.

the A/C unit appears the be the one that was installed when the house was built in 1990.

there is no known internal leak and the heating and cooling systems works well well.

I've attached a garden hose to the continuous flown pipe for the following reasons: to keep the rear of the garage from being wet; and using the water to water my flower bed toward the front of the house. There is a sound that can be heard when in the bathrooms, which are closest to the garage attic. the sound is similar to that of an opened water tap.