Toyota Landcruiser Prado GRJ120 with a 1GR-FE 4.0L V6 engine


No air conditioner, When a/c turned on after 5 seconds the A/c light flashes.
The air conditioning compressor clutch did not engage and subsequently the A/C light flashes.
The A/c Systems performance was cold and working fine, Then all of a sudden stopped working and light flashing.


The A/C compressor was checked for power and at the clutch with no power present only ground circuit for the coil, 12v power was applied to the compressor clutch and the compressor clutch kicked in indicating that there was no issue with the A/C Compressor clutch or Magnetic Clutch coil, and that the a/c refrigerant charge was full.

The Fuses were checked and the A/C Relay was checked, The high pressure switch was checked for open circuit, the front ambient air temperature sensor was check for resistance.
All testes carried out came back OK, It was now either the speed sensor on the compressor or the A/C Amplifier.

Fig. 1

Our PICO Scope carried out the function of testing the A/C compressors speed sensor, its function is to match the speed of the compressor with the speed of the engine so the A/C Amplifier knows that the a/c compressor is not seized or the belt is not slipping. Fig1 Shows the wave form from the Oscilloscope ( this will aid any new techs looking for issues with these Prado’s)

The Speed sensor is an a/c inductive pick up as the wave form shows. the testing done is with the compressor of the vehicle but could be done on the vehicle.

The System has now been tested for 90% of the parts testing OK, It was up to testing the A/c Amplifier. According to all the information sourced on the Internet and from Toyota spare parts division the A/c amplifier was present in the system under the glove box. We removed the glove box and found a few modules and boxes and decided to remove them Fig 2. Shows a module that was removed and was very hard to get out most people would not even both to pull it out due to its extremely hard to reach bolts. but after all the information acquired we thought we had to to fix the problem, After we pulled the module out we found that it was the Engine Immobiliser ECU, and that was not what was supposed to be there. Fig 2 shows the Immobiliser ECU.

Fig. 2

After 3 hours had gone by and no success we finally found a Workshop manual for a Toyota Tacoma ( Toyota Hilux in America) The workshop manual was for a left hand drive vehicle and showed the a/c Amplifier under the glove box on the R/H side of the vehicle which on our vehicle would indicate under the steering column, extensive checks we done to find this A/C Amplifier with no success, if any one has found the A/c Amplifier we would love to know where it is the parts catalogue shows it in the engine bay, But we fear this is wrong. We did find a box that resembled the picture, Rang the dealer and asked what the part was from the Part number found on the box and it was a resistor for the fuel pump.

All of this tinme and still no A/C working, we decided to further more consult the Tacoma workshop manual and check the wiring diagram for any thing we had missed. We did find a relay in the system called MG CLT, which did not mean any thin at the time but thinking back it stands for, MAGNETIC CLUTCH, we swapped the relay for the fog lights and indeed found that the a/c compressor switched on and stayed on, we checked the operation for the fog lights and the fog light did not work. The relay was a micro relay found in any ford or Holden, We swapped the MG CLT relay with a known good one and The system was now FIXED.


The fix Was the MG CLT relay, clicking on but not transferring the power to the A/C Compressor clutch. Very simple!

We are sure that we have given every body a fresh approach at checking the Prado’s A/C system and hope one day some one will let us know where the A/C Amplifier is located. The A/c Amplifiers Part number is 88650- 60721 we are thinking that it is not on this vehicle being a standard a/c system with out climate control.