c5 air con packed up

[sportingfiat]

hey all typical now its decidedly warm the aircon has packed up

when you press the button you can hear it click in but no fans or anything coming on, i have checked all the fuses but found nothing unusual

any ideas what to check, anything that is know to pack up ? ?

cheers
andy

[Paul-R]

I've just gone through the process of sorting my aircon problems so maybe mine was the same cause as yours.

Firstly, my A/C is the idependantly temparature settable for Driver and Passenger automatic type, I think yours is the same. I think you'll find that the air cooler is still working and if you travel along the road with the outlets set to windscreen only you can just about see a small patch of condensation above the outlets.

I''l quote from my previous postings elsewhere...

When I start the engine up if the speed is set to anything other than the lowest setting after a few moments the ECU shuts it down. At its lowest setting then one of the segments stays ilumminated but I can't feel any air movement and if I raise the speed then the ECU closes it all down.

I then got this reply (thanks Les), which pointed me in the right direction...

Hi Paul,
I suspect the fault will be the heater speed control module. It is situated in the right hand side foot well. It is about 2.5" * 1" * 4" It is held in with two screws near the end away from the plug. When you have removed it you will see it has a heat sink on the end. It is supposed to be replaced but I managed to repair the one on my brother in law's C5. The power MOSFET had failed. I could not find a source for the original MOSFET (STW80NF55-08)here in the UK. But I used a IRF3205VPBF ( RS stock code 540-9783) The original device is a TO247 package. The one I used was a TO220 package but I managed to bend the legs enough to fit in the PCB. This has been working for over a year now.
Les.

I was on holiday at the time and didn't have all my gear with me but was able to find the module as follows...

There appears to be two places it can be.

Assuming a RHD car:

1) Passenger footwell, RH side. Behind the carpet almost up behind the dashboard. You have to remove a fibreboard trim piece as well.

2) Driver footwell, LH side. A mirror image of the first above. It's more difficult to get at, of course, because of the pedals. The unit is held in by two hex head screws which are the same size as the screwdriver with replaceable bits (6.3mm, but 6mm is the correct size). This is where mine is but the others I've found are type 1 above. It was a bit difficult persuading the electrical plug off but a bit of shed blood later it came out!

and then...

I found the part in question - what a palaver to get it out! I suppose it would be quite easy if the pedals and steering column weren't in the way!

When I eventually got the unit on the table and took the covers off I found that one of the pins was discoloured from heat and was badly soldered. It had also partly pulled out out of the PCB. I'm on holiday at the moment but fortunately had my soldering iron with me (!) and had a go at resoldering.

Unfortunately, when I put it back in the blower still didn't work. I wasn't overly surprised as I wasn't happy with the quality of the solder joint, I need a hotter iron to melt the solder better. The power transistor might still be blown of course - it'll all have to wait until I get back to the UK.

At this point you can do a quick and dirty test on the blower unit by taking the two connectors off the module and bridging the pairs of thick wires (with the ignition on). The fan should blast out at full speed. In my case it didn't as there was no voltage coming down to the module but by taking a feed directly off the battery and bridging just the earthy side of the circuit I got the fan to blow.

A long and involved process later when I had taken the engine fusebox out and put it back and also resoldered properly the faulty pin on the control module I put it all together WITHOUT changing the MOSFET and it worked.

I think that you've got enough to get started there!