Case IH 133 – ATC (Automatic Temperature Control): Low pressure switch (-) input shorted to ground

The negative/ground signal wire running from the air conditioning (A/C) low-pressure switch to the control module has a short circuit to the chassis ground, or the switch itself has failed and is internally shorted.

• STX Steiger
• Case IH Magnum Series (235-340 Series 4, MX210, MX215, MX245, MX275, MX305)
• Case IH Steiger / STX Series (350-600 HP models, STX 430, 485)
• Case IH MX / TG Series

1. 1

   Inspect the A/C low-pressure switch and its electrical connector for physical damage, corrosion, or moisture.

2. 2

   Disconnect the electrical harness from the low-pressure switch and test the (-) signal wire running back to the ATC module for continuity to ground to check for a chafed or pinched wiring harness.

3. 3

   Test the low-pressure switch itself for an internal short to ground.

1. 1

   Locate switch

   Turn off the tractor and locate the A/C low-pressure switch, which is typically mounted on the suction side of the A/C refrigerant lines.

2. 2

   Disconnect connector

   Disconnect the electrical connector from the switch.

3. 3

   Repair wiring harness

   If the diagnostic checks revealed a short in the wiring harness, trace the harness back to the ATC module, locate the chafed/bare wire, and repair or replace the damaged section.

4. 4

   Prepare for switch replacement

   If the wiring tests good but the switch is internally shorted, the switch must be replaced. (Note: Check if the switch is mounted on a Schrader valve. If it is, it can be unscrewed without losing refrigerant. If not, the A/C system refrigerant must be safely recovered using an approved A/C recovery machine before removal).

5. 5

   Replace switch

   Unscrew the faulty low-pressure switch and install the new OEM replacement switch.

6. 6

   Reconnect harness

   Reconnect the electrical harness.

7. 7

   Recharge A/C system

   If refrigerant was recovered, pull a vacuum on the system and recharge it to the OEM specified weight.

8. 8

   Verify operation

   Clear the ATC fault codes and run the tractor's A/C system to verify proper compressor clutch engagement and cooling operation.