Dallas wrote:

I've got a real head scratcher.
Long story short: 18 zone, 24-volt AC commercial sprinkler controller
system.
One valve on the system won't operate anymore after running fine for years.
The valve operates when connected to a battery operated testing unit.
Voltage at the controller terminal going out to the zone shows 29 volts.
The wires from the controller at the valve (guessing 200+ foot underground
run, 14 gauge wire) show 27.4 volts.
There's enough current to give you a tickle if you grab the wires.
Connect the 27.4 volts to the valve and nothing happens.

Also dont overlook possibility of a stiff mechanism connected to the
solenoid, or a stiff solenoid due to leakage and corrosion.

A good way to drive solenoids is to use a capacitor to give them an
initial pulse of 2x rated voltage, which very rapidly drops to rated
voltage from the supply.

Really you just need to work it thru, divide and conquer until you know
where the problem is.


NT