Here Is Info On Air Con Debug Fix For 1994 Rav4 ( Keywords: Air Condi

[jtq4u]

Hey All,

I finally fixed my air con on my rav4 and learn't a lot in the process.. here it all is if anyone needs it.

========================================

DISCLAIMER

ALL INFO IS AS IS, and it's your own fault if something horrid happens because you trusted me. More fool you! you should always do a resistance check against earth before sending 12v down a wire or plug.. if it's less than 3 ohms I'd think carefully before doing it.. if it's less than 1 ohm then just don't that would be silly as a massive current will flow!

========================================

For completeness I post how I solved it:

The socket on the top of the compressor looks like this

looking from the top down

--------------

| o o o |

--------------

1 2 3

pin 1 is a signal to tell the engine the rpm of the compressor

pin 2 is an earth

pin 3 is the energize for the magnetic clutch.. should be between 3 and 4 ohms to earth

on the top of the reciever drier to the front right of the engine there is a 4 pin socket (low pressure sensor and something else unknown too). Removing the plug will start the right radiator fan going constantly (useful if the car is overheating and the fan isn't kicking in properly).

If everything is ok with the pressure sensor then pins opposite each other should be common (less than 1 ohm resistance)

looking down on the socket on the reciever drier

-----------------

| (1) |

| |

| (2) (3) |

| |

| (4) |

-----------------

pin 1 common with pin 4

pin 2 common with pin 3

In the smaller of the two fuse/relay boxes.. just marked relays there is a relay in the bottom left marked (MG/C) to force the compressor on place a wire between the bottom most pin (4 in the diagram below) and the +ve of the Battery. First check the resistance against earth to make sure you arn't creating a short. It should be between 3 and 4 ohms. It is much easier to force the compressor on at this point than at the compressor it's self.

RELAY MG/C

-----------------

| (1) |

| |

| (2) (3) |

| |

| (4) |

-----------------

Debugging air con:

1. using the instructions above check the pins are common across the reciever drier socket

This hints that the pressure is ok in your system

2. If possible do a pressure check of the low side using a guage (£10 off ebay). Ignore what it says on the

guage instructions as if you can't turn your compressor on then the pressure will not match the suggestions

it should be much higher >80. If your compressor can kick in then it will be in the suggested range

if the guage shows the pressure as low then DO NOT whatever you do force the compressor on as detailed

below because you will kill it. You must first top up the system with a mix of gas and oil (best to add some

oil too just incase).. you can buy kits containing both in one can on eBay. Get one with leak dye in too so

you can see where it leaks if it does.

now we have established the gas level is ok we can try and force the compressor on.

This will work if your pressure sensor is jammed off (pins not common).. and you have checked the pressure is definately ok.

3. remove the relay marked mg/c and resistance check the bottom pin to earth (see diagram of relay above) it should be 3 to 4 ohms. Do not proceed to connect a wire if it has a value less than this. If it has infinate resistance check that the plug is connected to the top of the compressor.

4. place a wire or probe into the bottom pin (as shown in the diagram above) and place the other wire against the +ve of your Battery. You should hear a load click.. this is the magnetic clutch enguaging and should make you feel happy. remove the wire

5. Turn on the engine and repeat step 4. you should feel the pipe with the (L) marked cap on it get very cold.. this shows your air con is working.

If there is no loud click when connecting to the relay you can try making the connection at the compressor it's self by exposing the wire connected to pin 3 shown in the diagram above (with the plug still connected to provide earth in the pin 2). Also check pin 2 is connected to earth by resistance checking it to earth and confirming a value less than 1 ohm. If there is still no loud click the chances are that the magnetic cluctch is broken and needs replacing. Check that the wire to the lump on top of the unit on the black bit next to the pulley is not damaged.

If you were successful in making the unit work by forcing +ve down the MG/C relay but with all your test equiptment removed it still doesnt' work, and the pressure sensor has its pins common.. then it may be the rpm sensor on the compressor. This is the problem if the air con button stays lit for about 2 seconds then starts flashing. The computer waits a couple of seconds then checks the RPM is within 10% of the engines outputted rpm on the belt. If it isn't then it shuts down the compressor. You'll see that pin 3 on the compressor is 12v for the first 2 secs then goes to 0 when the light flashes. If there is never 12v on pin 3 it may be that the relay mg/c is defective (or missing as mine was!).

one check of the rpm sensor is the resistance of pin 1 and 2 on the compressor with the key out of the ignition. It should be >100 ohms. If it is Infinate or 0 then something is certainly wrong.

I beleive that the sensor is sadly internal to the compressor and probably requires a total unit replace. If you are certain (and the air con man confirms from computer check) that it's the rpm sensor thats broken (and not it's amplifier or connection to ecu) then I guess you could wire up your own switch to control relay mg/c and the 2nd fan.. though as you are bypassing the pressure sensor you would need to pressure check your system regularly to avoid burning out the compressor with low pressure (but hey you were going to have to replace the thing anyhow).

Hope this info helps people I wish it had been there for me!

James

[dawesy]

very good write up there, very useful and informative.

glad you sorted the problem chap