Mk1 Ford Focus A/C problem

Gaygle

Gaygle

Gaygle

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Calling all MK1 Focus guru's.

A friend of mine has a 54 plate 1.6 Ford Focus. For quite a while now he's had a problem with it in that if he turns the air conditioning on, it lowers the RPM a lot, sometimes to the point of stall. I offered to have a look at it to see if there was anything obviously wrong. I've cleaned the ICV, inspected the boot from the airbox to throttle body for splits and cleaned the throttle body and it has done nothing to help the problem.

The car drives and idles perfectly when the air conditioning is off, but as soon as you push the button to turn it on, it lowers the RPM, then the clutch disengages and the revs return to normal, then it tries to engage the A/C compressor again, then it lowers to the revs to near stall, so it quickly disengages the compressor again and so on and so on. It's almost as though the compressor is putting such a load on the engine, that it can't handle it.

I would have started pointing the finger at the air con compressor, but it is fine for the first 2 minutes on a cold engine and only starts playing up when the cold start procedure is over and the revs settle at ~800rpm. The other thing that i noticed is that the fan (single fan car) doesn't turn on when the A/C turns on, nor does it start even when I got the engine coolant to 119c!

So, like I said, can any Focus guru's lend a hand?
 
Yeh, that might be a plan. I know low gas can cause weird problems with A/C but is there any chance it would it be responsible for this? The other thing is that if you are driving along, say on a motorway, and turn the aircon on - it works ok. It's only if you let the revs drop ie. you come up to a roundabout or even just depress the clutch pedal, that it is in danger of stalling.
 
The car's ECU should ‘know’ when the a/c is active and raise the RPM ever so slightly to counteract the extra drag from the compressor. I cannot remember what input the ECU takes from the sensors/switched to determine this, I think it has a combined high/low pressure switch which senses system pressures.

Apologies for being vague, any A/C specialist should be able to diagnose the issue & know what to look for as it should be pretty easy. A/C isn't that complicated
 
MatteH Oxford said:
Apologies for being vague, any A/C specialist should be able to diagnose the issue & know what to look for as it should be pretty easy. A/C isn't that complicated
Click to expand...
How much is a mk1 focus worth ? (guessing somewhere between £100 to £400)

Is it really worth paying for a specialist to work on an old mk1 focus...
 
I *think* there is a wire back to the ecu that is tapped into the A/C compressor relay circuit, when you hit the A/C switch it then ‘knows’ the A/C is active. Subsequently, the inputs from the pressure switch cycle the ecu to turn the A/C compressor on/off.

Anyone who works on them regularly will know exactly where to look and check. All you would need to do is either earth or supply 12v to the correct ECU pin and it should raise/lower the RPM as if the A/C is on. Simple really.

The Focus is a little after my time with Ford, I worked on Fords during the mk1/2 Mondeo era.
 
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Looking back at your post, the engine cooling fan should be an issue if it is not working. I'm sure the ECU raises the RPM when it is running, it is linked to the A/C system too as it usually runs continually with A/C switched on.
Either low or high speed depending on system conditions.

Check the fan earth/12v supply. It's easy to check the motor works with a fused 12v jumper wire (make sure the earth is ok though).
 
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Thanks for the replies.

Yeh I'm sure the fan should have kicked in when the AC turned on and if not, definitely should have kicked in when the coolant was at 120c! The weird thing is the engine doesn't overheat, even on a hot day in traffic!

It's an electric fan so why would the RPM have to increase for it?
 
It requires a fair amount of electrical power to run the fan and it puts quite a load on the alternator, so the idle speed often needs a slight bump up to counteract that.
For example, the fan relays are often rated for 80 amps (for two fans systems). I think a single is either 40 or 60 amp.
 
The A/C in my mk1 focus died around 4 years ago. Thought the car wasn't worth much and I wouldn't have it much longer so didnt bother getting it looked at.
Here I am 4 years later still driving it. Hindsight is a wonderful thing!
 
On the cooling fan connector you should have a couple of wires, Ford tend to use green for the positive 12v and they will likely have either a red or yellow trace line. Earth will almost definitely be black. One of the green wires will be a direct link to the 12v supply at the fusebox, the other will go through a resistor to provide the lower speed setting so expect around 9v on that wire. One or the other will be 'live' when the a/c is on or the coolant temperature is over 100c (somewhere around 98c it should cut in from memory for most Fords).

Seeing as it doesn't work at either speed, I'd suspect the fan motor *edit* or the earth of course, the wire should trace back to a point on the chassis close to the connector. I'm not that familiar with Foci but if they are like most Fords of that age I'd expect some corrosion at least! :D
 
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Thanks for your insight into this. Very helpful. O guess fixing the fan could be the first step then see what happens!
 
I owned a MK1 Focus (1.6) a few years ago and I remember having a similar issue where on idle there would be noticeable vibration that could be felt throughout the car at only 800~RPM and only when the engine was warm, but it would then be twice as worse when using the AC. However as soon as you blip the acceleration it would disappear until you take your foot off it again.

While this may not quite be related to your fault, but besides hearing that in my case that one of the engine mounts was at fault - apparently around 10 years ago, Ford released a new ECU update for the MK1 era which was particularly directed towards the 1.6 engine variants. The new ECU update supposedly altered the warm idle RPM from the 800~RPM range to just slightly higher at around 875~RPM - the old ECU software reportedly struggled to keep on top with added electrics when in use (especially the AC as mentioned, but also lights etc.), and this fix was reported to cure the idle vibrations. Apparently it was a common fault on these 1.6 models.

I never had the ECU update carried out on mine as the replacement engine mount (rear dog bone one that connects to the gearbox) near enough cured my issue, again this engine mount failing was also another common failure point on these.

Just some food for thought for you.

Liam.
 
AFAIK the ECU update was to prevent rough idle, the extra loads on the engine from A/C etc shouldn't cause the engine to stall without it.

Regarding the fan, it likely only has one permanent 12v feed that is red in colour, and a thin blue 'trigger' wire from the ECU turns the fan (transistor controlled, newer circuit design than I'm used to!) on depending on coolant temperature & A/C system conditions. The earth wire is still likely black.
 
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