Parts for your 1991 Mitsubishi Pajero-Ac compressor

1991 Mitsubishi Pajero A/C Compressor — What It Does and How to Look After It

Based on Mitsubishi’s factory service manuals, the Mitsubishi ASA parts catalogue, and period application data from Denso and Sanden, the 1991 Mitsubishi Pajero was supplied with a belt-driven air-conditioning compressor. So yes — an A/C compressor is relevant to this model, and it’s a core part of the air-con system.

The compressor’s job is to circulate refrigerant and compress it into a high-pressure, high-temperature state so the condenser can shed heat and the evaporator can deliver that crisp, dry air into the cabin. On the 1991 Pajero, it’s driven by the engine via an accessory belt and switched by an electromagnetic clutch. When the system calls for cooling, the clutch engages, when it’s satisfied, the clutch disengages to reduce load and fuel use.

Because many 1991 vehicles were originally charged with R12, owners will often find their Pajero has been converted to R134a. That’s perfectly normal, but it means the right oil and seals are a must. R12 systems used mineral oil, R134a conversions need PAG or POE oil (as specified during conversion), and all O-rings should be upgraded to HNBR. A receiver–drier replacement is strongly recommended whenever the system is opened, especially when fitting a new compressor.

When replacing or servicing the A/C compressor on a 1991 Pajero, a solid approach looks like this:

• Identify the refrigerant in the system (label under the bonnet or by testing) and match the correct oil type and quantity to the compressor.
• Replace the receiver–drier, flush the lines and condenser where appropriate, and consider the TX valve if performance has been patchy.
• Fit new HNBR O-rings, check belt condition and tension, and set the clutch air gap to the service manual spec.
• Evacuate with a vacuum pump, verify no moisture ingress or leaks, then recharge by weight.

Typical symptoms of a tired compressor include noisy operation (grinding or squeal), intermittent cooling as the clutch slips, metal debris in the old drier, or a tripped pressure switch. Leaving it too long risks seizing, which can throw a belt or contaminate the whole system. With good servicing—clean condenser fins, correct belt tension, timely drier changes, and proper refrigerant charge—the Pajero’s A/C compressor will keep doing the hard yards for many more kilometres.

• What refrigerant does a 1991 Mitsubishi Pajero use?
  Many left the factory with R12. Most road-going examples today in Australia and New Zealand have been professionally converted to R134a. Check the under‑bonnet label or service history. If converted, ensure the correct oil (PAG or POE as specified) is used and the charge weight reflects the conversion notes.
• How can someone tell if the A/C compressor is failing?
  Common signs are clutch chatter, excessive cycling, weak cooling at idle, or metallic noise. Oil stains around hose fittings, a slipping belt, or debris found in the receiver–drier also point to internal wear. A proper pressure test and current draw check will confirm the diagnosis.
• Is it safe to drive a Pajero if the A/C compressor has seized?
  If the compressor has seized, the accessory belt may burn or break. On some setups, that belt also drives other accessories, so it’s best to isolate the compressor or repair it before driving. If it freewheels with the clutch off, you can drive, but avoid using the A/C until it’s fixed.