Ac cuts in and out - 2006 Chevrolet Express

first off learn how AC works, for sure this, set of hard logic, in the system for self preservation.
and if you had used the OBD2 SCAN TOOl first after fuses checked
you'd already know this.

1. high/low, R134 pressure switch tripped saving the full destruction of the compressor. a volt meter finds this truth also.
2. the controller AC also cuts AC if engine overheats or the sensor lies.
3. the control AC cuts AC at wide open throttle.WOT
4. AC cuts AC if engine IN gross DTC errors, or in limp-home mode to protect it and the driver, so more power is on tap from engine.
5. evap core sensor , sees freeze up and icing, Ice can do damage so it cut the compressor dead(means clutch off line)
6. the controller detects ambient temps WAY to low and cuts AC.
7. The dash controller AC is failing, but manual AC? not really if it's lamp glows for AC , the main controller is BCM on most cars.
8. the dash HVAC blower must not be dead or AC stay off line

A power feed wires must be shorted to ground at some point . Have you carefully checked for open insulation along the wiring ?

if on and off consistently [short cycling ] the usual cause is low or short on freon others are low pressure sensor switch -or clutch failing but the usual problem is freon level

go with the ac guy
there are systems that prevent the ac compressor working
high pressure switch which cuts the ac clutch if the head pressure goes too high
low pressure switch which cuts power to the ac compressor if there
is no gas in the system
climate control systems which cut power when the ac is not required
fuses to the ac system
get a better explanation or seek advice from other ac mechanics

It maybe a low gas pressure fault as low pressure will not allow compressor to drive.

fuses are in the operators guide.
the glove box guide is free at all honda dealers and is online.
get one and keep it in the car,,, "safety"
the tests for A/C start at the fuses.
the blower , must blow.
then is the compression clutch engaged or not.
post back the clutch status and we can work thru the 100 pages
in the FSM.
or read it your self at alldata.com
the fsm is free. see it here
1st line
http://hondatech.info/downloads/Auto/Manuals/Civic/

see page 62 for schematic of the A/c
as you can see the PCM decides when the clutch is active
but there are 6 ways, for it to decide, not to run AC/

on the 99 there is a cab themostat , (hark) that can stop AC
and so cant he freon hi/low switch, do not bypass this device !!
see page 62-2 for stat schematic.
see page 62-3 (theory)
if the out door temp drops below 37F it cuts AC.
if the engine overheats, cuts AC
if the engine is overloaded, it cuts AC (see OBD2 scans for load factor (hills)
if the evap core freezes , most AC cut.
low freon. cut
too high? cut.

These are what a tech calls, AC permissives.
if the clutch is dead, we are all over them.

the ac clutch engages any time a defrosters on if you have a ac problem unhook the ac compressor that should take care of it till you have ac fixed

check for the cut off switch or sensor on the a/c plumbing to see if normally closed or normally open, and if it is causing the the AC Cut of relay to be energized permanently.

See if disconnecting the switch on the plumbinug changes anything. Or if using a test light to ground out the terminals does anything different on the AC system.

Yes. You can cut it, the only thing it runs is the A/C Compressor.

its low on freion thats why it cuts on and off