z writes:
OK, here's the deal:
newish (to me) house. bathroom has two sinks next to each other, with
identical Moen faucets. both hooked up correctly. left hand faucet
works normallly, right hand faucet has hot water come out when lever
is to the right, cold to the right, i.e. backwards. but, i repeat,
it's hooked up correctly, just like left hand (not backwards) faucet.

hot water shutoff valve shuts off hot water and cold water shutoff
shuts off cold water, despite backwardness. hot water pipe gets hot
when hot water flows on either faucet. supply lines are not crossed up
under the faucets, i looked right up there. I pulled out the
cartridge, it looks symmetrical, pretty simple deal, a hole in the
left where the hot water comes in and a hole in the right where the
cold water comes in.

The fixed part of the cartridge is symmetric about the centre, but the
rotating valve part of the cartridge is sort of half-round in shape, and
the cutaway portion needs to face in the direction the handle faces.
One of yours is backward.

You need to install the handle on the cartridge the other way around.
Take the handle off that faucet, rotate the shaft of the cartridge 180
degrees, and put the handle back on.

The place where the handle mounts on the cartridge shaft is not keyed,
so the handle can mount either of two ways. This is a feature, because
different Moen faucets with different handle designs (lever vs.
directly-attached handle) use the cartridge oriented differently. To get
things aligned correctly, there's a mark on one side of the shaft but
not the other, and you're supposed to match these when replacing
cartridges. Someone obviously didn't.

(This also means that if you happen to get hot and cold swapped when
plumbing a new Moen faucet, you can get it to operate correctly just by
rotating the cartridge to the "wrong" orientation - you don't have to
fix the plumbing).

Dave