Case IH 134 – ATC (Automatic Temperature Control): Low pressure switch open for > 1 minute

The Air Conditioning (A/C) low-pressure switch has remained in an open electrical state for too long. This switch monitors the refrigerant pressure on the low side of the A/C system and cuts power to the A/C compressor clutch if the system pressure drops below a safe operating threshold to prevent the compressor from running dry and seizing up.

• STX Steiger
• MX Magnum
• Magnum 235-340 (Series 4)
• 7000-9000 series
• STX Steiger (350-600 HP)
• 485
• Maxxum Series
• Puma Series
• T8.xxx Series
• TG Series

1. 1

   Check Refrigerant Charge: Connect A/C manifold gauges to the system. A low refrigerant charge (due to a leak) is the most common reason the low-pressure switch opens. If the static pressure is too low, the switch is doing its job and the system needs leak-testing and recharging.

2. 2

   Inspect the Wiring Harness: Check the wiring and connector at the low-pressure switch (usually located on the evaporator outlet line). Look for broken wires, corrosion, or loose pins. The ATC module monitors this circuit, and a broken wire will mimic an open switch.

3. 3

   Test the Switch for Continuity: Most Case IH low-pressure switches are Normally Closed (NC). If the A/C system has a proper static refrigerant charge but the switch tests open (no continuity across the terminals) with a multimeter, the switch has failed internally.

4. 4

   Check for Related Codes: Ensure there are no other ATC codes present (such as 130, 131, 132, or 133), which would indicate a direct short to ground or power in the switch wiring rather than a standard open circuit.

1. 1

   Locate the Switch

   Find the A/C low-pressure switch, which is threaded onto the low-pressure A/C line (often near the evaporator outlet or the compressor suction line).

2. 2

   Disconnect Electrical Connector

   Unplug the wiring harness from the switch.

3. 3

   Determine System Pressure Status

   Check if the switch is mounted on a Schrader valve fitting. Many modern Case IH tractors use a Schrader valve under the switch, allowing you to unscrew it without discharging the A/C system. If there is no Schrader valve, you must safely recover the refrigerant using an A/C recovery machine before proceeding.

4. 4

   Remove the Switch

   Unscrew the faulty low-pressure switch from the fitting.

5. 5

   Install the New Switch

   Lubricate the O-ring on the new switch with a drop of clean PAG/refrigerant oil. Thread the new switch onto the fitting and tighten it to the OEM torque specification.

6. 6

   Reconnect Wiring

   Plug the electrical connector back into the switch.

7. 7

   Recharge System (If Applicable)

   If the system was discharged, pull a deep vacuum on the system and recharge it with the exact OEM-specified weight of R134a refrigerant.

8. 8

   Clear Codes and Test

   Clear the ATC 134 fault code from the cab monitor/controller. Turn on the tractor and the A/C to verify that the compressor clutch engages and the cabin cools properly.