Emergency Stop Circuit Open or E-Stop Activated

Common Symptoms

• WS Controller LCD displays E050 and the unit will not crank
• Red fault light is on and the panel is locked out from starting
• Compressor shuts down immediately mid-operation and will not restart
• Panel shows RUN command accepted but engine never fires
• Remote E-stop mushroom button is visibly pressed in or twisted to the locked position
• Unit was running normally then tripped suddenly with no other warning codes
• Audible alarm sounds and unit coasts to a stop

Probable Causes (Ranked by Likelihood)

• Remote E-stop mushroom button pressed or physically latched in the depressed position Very Likely
• Panel-mounted E-stop button on the control box pressed and not released Very Likely
• Broken, corroded, or disconnected wiring in the E-stop safety loop between remote pendant and controller Likely
• Faulty or damaged E-stop push button contact block that is no longer returning to its open state when released Likely
• Loose or corroded connector at the WS Controller terminal strip where the safety loop lands Possible
• Water intrusion into the remote pendant or junction box causing a short or open in the E-stop circuit Possible
• WS Controller input card or I/O board fault misreading the E-stop loop as open when the loop is intact Less Likely

Step-by-Step Diagnostic Procedure

1. Start at the obvious place. Walk around the entire unit and check every E-stop mushroom button, both on the main control panel and any remote pendant or trailer-mounted stations. Twist and pull each one to confirm it is fully released and in the OUT position. Most E050 faults clear right here.

2. If all buttons are released and the fault persists, cycle the panel selector switch to OFF, wait 10 seconds, then attempt to restart. The WS Controller requires a clean OFF cycle after an E-stop event before it will accept a new start command. Watch the LCD for the fault to clear.

3. Inspect the E-stop wiring loop from the controller terminal strip out to each remote station. The E-stop circuit is a normally-closed loop. Any open in this loop trips E050. Look for pinched wires under trailer components, bare conductors touching frame ground, or corroded ring terminals at junction boxes.

4. At the WS Controller terminal strip, locate the E-stop loop terminals (labeled ES or ESTOP in the wiring diagram on the inside of the control panel door). With a multimeter set to continuity, measure across those two terminals with the machine in OFF. You should read continuity (loop closed). An open reading means a break exists somewhere in the loop wiring or a button contact has failed.

5. To isolate the fault, disconnect the remote pendant cable at the main panel connector and place a jumper wire across the two E-stop loop terminals on the terminal strip. If the fault clears on the LCD, the problem is in the remote pendant cable or button, not the controller. If the fault stays with the jumper in place, the WS Controller input itself may be the issue.

6. Inspect the E-stop button contact block on any suspect station. With the button fully released (out position), measure continuity across the NC contact terminals on the back of the button assembly. You should have continuity. If you read open with the button released, the contact block is worn or damaged and needs replacement. These are standard 22mm or 30mm contact blocks available from any electrical supplier.

7. Check for water damage at remote pendants and junction boxes. Corrosion on the terminals is enough to create a high-resistance open in the loop. Clean terminals with electrical contact cleaner, apply dielectric grease, and re-test.

8. If the fault cannot be cleared through wiring and button checks, connect to the WS Controller LCD diagnostics menu to confirm the fault is E050 and not a secondary fault masking something else. If you suspect a controller I/O board failure, this step requires a Sullair service tech with access to controller-level diagnostics.

Frequently Asked Questions