Need help with water system question, 88 pt40 96"

[hodakaguy]

We have been running our 88 pt40 on dirrect hook up water with 40psi
for around a month now, yesterday the water pressure dropped very low
in the coach. The inlet psi is still 40. If we turn the pump on we
have lots of pressure. With the pump off we will have pressure for
just a second when you first open something up and then it drops off
rapidly. If we kick the electric air compressor on we will get
pressure for a second and then air blowing through the lines. Is the
air compressor tied into the fresh water somewhere? The switch next
to the fresh water connection is not on fill. Could a solenoid be
stuck? Where shoud I start looking. Thanks in advance for the help.

Tom C. Wa state