Astra mk4 cooling electrics

Right, I am not totally familair with the Astra system, but can tell you that the engine ECU is wholly responsible for cooling fan actuation, and air con compressor clutch actuation, based upon signals from the high and low pressure switch, engine temp, and interior temp sensor through the fan control module, and compressor clutch relay.

I would feel that your fuse blowing is down to either a short in the wiring to, or the compressor clutch windings themselves. I'd disconnect this and meter it, having a good tug of the wiring, and the clutch itself to see if you can find any short. Repeat the same for both cooling fans, although you dont mention any problem with the fans not running for coolage of the engine.

After this, i'd code read the ECU as soon as you can after the MIL lamp doing its flashing and see if that points you in any direction, then (if possible) opening up the control unit and actuating the relay contacts manually to see if you can get the a/c to kick in at all.

If it works ok (if it doesnt begin to blow cold within 15-30seconds stop, as you are bypassing the low gas safety switch doing this, and you may not have any gas which will damage the compressor) then pull out the relay and with the help of a wiring diagram see if the ECU is pulling to ground the relative terminals in an effort to fire up the a/c clutch and rad fans or not. If it is, then it points to a faulty module.

Tim..

all quite in depth ........ another way is to use a power probe and see if you can activate the compressors magnetic coupling also check that the fan actually works when given a supply as it is the obvious suspect here showing signs of damage

This age of astra with the 2.0Di had a seperate cooling system ECU located in front of the nearside inner wing. It was common for them to get filled with water and corrode. This normally led to cooling fans not working, and the MIL being on constantly.

From the fault described it sounds more like a fault with the air con compressor clutch, as this is the only thing to cut in as soon as the a/c is turned on (there is normally a delay before the cooling fans cut in).

moray

Thanks very much everyone who replied. I didnt think about looking at the compressor clutch side of things. From looking at the circuit diagram the fuse that is blowing is on the same part of the cooling circuit as the clutch. The fan is on a different part of the cooling ecu that doesnt seem to be connected. I disconnected the power to the compressor and tried turning on the aircon and the fuse didnt blow. There was about 14.5 volts across the two wires on the ecu side. I reconnected the cable and the fuse blew.

At that point I thought it must be the clutch shorting out. So I reconnected everything put in a new fuse thinking that if I didnt try to turn on the a/c it wouldnt blow. When I got back though the fuse was blown! I wonder if my turning on the internal fans caused the cooling ecu to make contact with the clutch or something.

Anyway tommorow i'll disconnect the compressor power again, go for a drive, try the fans etc and see what happens. Unfortunately my ability and equipment doesnt really extend to getting the compressor out. One thing im pretty sure of now the cooling fans side of things seems fine, they cut in at 92ish degrees with or without the fuse. The circuit diagram says the wire from the fuse is aircon only.

The aircon specialist said the system had coolant ok so I think I could try throwing the clutch manually. I've only got basic gear though, I want to try and test for a short across the clutch. Im planning to run a wire from the battery with a fuse inline to the clutch input and earth the other clutch cable and see if that fuse blows. Does this seem sensible? I realise fuse blowing isnt a great diagnostic tool! Im not really sure how compressors and clutches work are they integrated as one unit?

thanks again

Jim

Using a couple fused jumper wires is as good a way as any to try the clutch. You don't have to run the engine to check the clutch is working. If you connect the clutch to the battery, if all is working well, then you should see the clutch snapping closed.

Some clutches can be replaced. Best way to find out is to ask vauxhall if you can buy the clutch seperately.

moray

You can obtain the clutches seperately. The only downside is that some special tools are required to replace it....

Anthony Remove eight from e-mail to reply.

Thanks, should be cheaper than a whole new compressor though!

One more question any idea what kind of current a working or shorting clutch should use?

Jim

A working clutch should be in the 5- 8 amps area.

Tim..