(T) Air Conditioning Works Intermittently

Hi Guys,

Can anyone give me any ideas which I can pass on to my local main Fiat dealer to help them fix an intermittent fault with the air conditioning on my Stilo JTD?

About a month ago, thinking that low gas was what was causing my air conditioning not to work, I got the gas recharged at a branch of Budget. It worked great when I drove away, but then the air con started working intermittently – sometimes it worked when switched on, but only for maybe 20 – 30 minutes then the air was no longer cold. Most of the time it did not work when I pressed the button on the dashboard. I therefore concluded that it must be a mechanical or electrical fault which would need to be attended to by my local Fiat dealer.

I took it the dealer on Thursday – they did a diagnostic check and said the only problem was the gas needed topping up. £55 + VAT later and away I went, nice and cold. But an hour later it stopped working again!

Back to the dealer on Friday and 4 hours later I got a call to say that after extensive testing there was no fault found with the air con. (It wasn’t working on the way to the dealer). So I duly collected the car, drove off nice and cold for about an hour. Then it stopped working again and I could hardly see out when the windows steamed up when it started pouring!

Today, for most of the time it hasn’t worked when I pressed the switch. There is a quiet “click” when pressing the button on the dash but nothing from the engine and no change in the revs when idling. Other times it does work – the tickover changes and something seems to be happening under the bonnet! But it doesn’t last any more than about 30 minutes.

Has anyone experienced the same symptoms? I’m going to go back to the dealer on Monday or Tuesday - Does anyone have any ideas / tips that I can pass on to them? I appreciate that intermittent faults are the hardest to trace so any help will be gratefully received.

Air con problems fall into 3 categories - gas- electrics- mechanical
GAS
As you've eliminated the refridgerant gas (although i would ask why they keep topping it up and charging you if there's no leak and it's not fixing the problem) then they've done it enough times to realise it's not that

The fact that the clutch doesn't engage AND the tickover does not go higher even though the gas pressure is correct then it's an electrical problem as they have different supplies so it could be a cheap and cheerful repair. The fact it works for 1/2 hour but then drops out after something warms up sure sounds electrical.

Intermittent faults are easy as long as they stay not working so you can fnd them
What I would do is, once the air con prematurely stops then just simply start at one end, either where the power starts or the earth end and check through where the electrical power stops and then you know you have the location of the fault. An acupuncture probe is brilliant for this and very quick. You don't even need to disconnect anything. See guides again


MECHANICAL
Too large an air gap on the compressor clutch can cause drop out of the compressor. Check for power feed at the clutch but it's not likely to be this from what you've experienced as the tickover would still raise regardless


ELECTRICAL/MECHANICAL
The linear pressure switch at the front driver's side detects the gas pressure and will prevent compressor operation if the pressure is too low or too high


Looks similar to this
You can bypass the linear pressure switch and put in a variable resisitor like this with wires attached

the same as I explaned in my Stilo Guide for testing the eng temp sensor and you can make the air con start regardless of the gas pressure. Using pins 1 and 3 on the connector you can simulate the voltage being too low and compressor not starting, then just right and compressor starts or too high and compressor shuts down again all manually controlled by your variable resistor but do it just for a test of the switch and not permanently

ELECTRICS
SUPPLY
Possible electrical supply problem so take out the air con fuses and inspect for corrosion, have a good look at the contacts. There's a lot of fuses in the sytem
Fuses F16 compressor relay feed
F19 Compressor main feed
F31 and F8 Heater fan feed (not really causing your problem)
F49 Air con switch feed


COMPRESSOR CLUTCH
Listen for the distinctive "clack" of the clutch when you select air con. When the air con drops out check if electrical supply is still present at the compressor clutch. If it still has electrical power then you know all the electrics are fine and it's the compressor clutch- probably air gap.

RELAYS
Take out the relays, clean and inspect the contacts Relays T5 T8 and T9

EARTHS
Check for bad earths particularly the ones for the relays

Hi Deckchair5,

Many thanks for your quick and very detailed reply. I’ll print it off and take it with me when I go back to the dealer.

I was out for most of today in the car. It was doing the same – air con would work for a while then stop. If the car was left for a while, it would work again for about 20 minutes. Hopefully using your expert advice my dealer will be able to fix it once and for all during the week.

I’ll let you know how I get on - Thanks again!

One thing to check,
does your cooling fan kick in when you turn the aircon on?
lift the bonnet, turn engine on, then switch aircon on..... after 5-10 seconds the rad fan should start spinning to draw air across the condensor.

If it doesn't then you may have the same problem i had recently, See thread titled "Aircon mystery" in tech section.
i was told by my independant aircon engineer when he regassed mine and found my fan not working, that you shouldn't use the system if fan duff as it could damage other components.

if you've been using yours with the above problem, it COULD be something is cutting out after 30 is mins or maybe a safety cut off.

worth checking!

6th visit to the dealer lucky... Once they'd actually seen the A/C not working they initially tried replacing the relay, but it wasn't that.

The fact that the relay didn't fix it, and something to do with a voltage reading without the relay in place (I was never any good at physics at school), seemed to indicate that it was likely to be the pressure switch.

The dealer had to order one in and it was fitted on Thursday - it worked!

So apart from the front suspension snapping (replaced free of charge) and 2 sets of tyres, an A/C switch and re-gas are the only non-planned service costs in 50,000 miles - pretty good going

Thanks again for your input.

Glad it's now working.
It's really easy to check out the linear pressure switch though (see my post above) and they should have identified that was the problem within 10mins.