On Jun 1, 12:20*am, DerbyDad03 wrote:
It's 80 degrees in my house with 58% humidity. *Time for some AC.

Comfort 90 Max (Rheem) with Central Air

2 questions:

1 - With the fan set to "On" and the temp set to 70, I turned on the
AC. Here's what it does:

The blower will run for about 20 minutes (I didn't time it) and then
shut off for about 30 seconds. It does this continually and it's been
doing it for at least a couple of years. I first noticed it last
summer but I can't honestly say whether or not it's been doing it
since the unit was installed 5 years ago.

It only does this when the AC is on, not when the heat is on or when
the blower is set to On just to circulate the air. It's only when I'm
using the AC does the blower take a break.

Is this normal?

Every system I've seen, if you set the fan to on
it stays on continually



2 - I checked the temperature differential between the return trunk
and the plenum just above the AC coils.

77 in the return trunk, 64 in the plenum, except when the blower turns
off (see above). When the blower turns off, the plenum temperature
drops to 59. After the blower come back on (~30 seconds later) the
plenum temperature goes back up to 64.

What do think about that differential?

Seems on the low side. Somewhere around 18F is more typical.
But it depends on how much air is moving, ie the air handler size,
the speed it's actually running at, together with the cooling system
capacity.