Low voltage solenoid wiring

[Macklin]

Hello,
I recently started doing some work for a neighbor helping out with their carwash. It's 2 bays of self serve. They were having an issue with one of the solenoids not working for the engine and tire so it wasn't getting any air pressure, just the chemical drizzling out of the wand. I checked voltage and the solenoid was getting 17 v. I noticed that the jumpers on the terminal block were little wires with what looked like small resistors on them. I put a regular wire jumper on, a

 

[Keno]

Fairly certain those are diodes used to limit direction of current flow.

 

[Macklin]

Fairly certain those are diodes used to limit direction of current flow.

Gotcha, that would make sense. Could they go bad and limit my voltage to 17 V i stead of 24?

 

[MEP001]

Car washes and the solenoids they use are typically 24V AC. You can't use diodes on AC voltage. It turns it into pulsating DC.

Are there pumps that come on when a low pressure function is selected?

 

[Greg Pack]

Looks like part of your first post was snipped off. I'd like to know where the wires go. Seeing diodes on a solenoid bank makes me think someone was trying to prevent current flowing back, if that is the case that is something best accomplished with a relay, but looking at the wiring here this doesn't appear to be a typical setup. Are the solenoids 24 AC or DC?