Air con forces engine to surge 3000rpm! Help!

[Mickey74]

My car is a 2002 1.6 petrol v40 estate

Yesterday, when I turned on the air con, my engine revs started surging up and down (up to 3000rpm !) without any extra pressure on the accelerator pedal. This happened both when idling and cruising speed. When I turned off the air con, then the surging stopped .

I have no engine fault codes, my engine temperature is normal.
The only thing I have noticed, before this started, is that the force of the air from the air con sometimes dropped off and recovered (otherwise the air is cold). I guess it can’t be the idle control valve as it also happens when cruising ? Also, as the accelerator pedal response is fine, I assume it can’t be a clogged throttle body?

Any ideas if this is a classic air con problem ?

Any help would be greatly appreciated !

[bobthecabbage]

I don't know what this is but I would think about the following.

Air con clutch slipping,
Air con needs a recharge,
Battery condition poor (to power fan on radiator when not enough air flow for air con).
Alternator problem

Sounds like ECU is giving more fuel to the engine for the load of the compressor but the compressor load is dropping out/uneven.

Other loads coming and going could be the alternator if its compensating for a weak battery when the fan kicks in.

I'm guessing this doesn't happen when driving?

This is just an initial 'throw something and see what sticks' thought process. I don't know much about petrols or your particular engine so I can't really help there. It does sound like either an unusual loading of the engine or an inability to respond properly to changes in load.

I tend to switch my aircon off when stationary because I don't like the fan kicking in and out and making all the lights dim (less so after a new battery).

[Mickey74]

Air con clutch slipping,
Air con needs a recharge,
Battery condition poor (to power fan on radiator when not enough air flow for air con).
Alternator problem

Thanks lots for your ideas Bobthecabbage !

I don't know anything about air con but I will research slipping / recharge. Could it also be a failing compressor? (I don't have any receipts for work done on the A/C since the car was born.

Sounds like ECU is giving more fuel to the engine for the load of the compressor but the compressor load is dropping out/uneven.

Also sounds like a clever and perfect description of what is happening.

I think the alternator must be working fine as my year old battery still has a charge of 12.66V when I measured it yesterday.

If any other ideas occur please let me know!

[Mickey74]

I'm guessing this doesn't happen when driving?

Yes, bobthecabbage ! While driving or standing still with the engine turning.

[pierremcalpine]

Two guesses:
1) the wiring to the ac clutch has an intermittent short or is not fully plugged in
2) The compressor is self-distructing due to old age and should be replaced pronto. If you leave this too long, pieces of metal will begin to circulate throughout the system forcing you to replace more f'n components in the ac system.

These are guesses only.

[Mickey74]

Two guesses:
1) the wiring to the ac clutch has an intermittent short or is not fully plugged in
2) The compressor is self-distructing due to old age and should be replaced pronto. If you leave this too long, pieces of metal will begin to circulate throughout the system forcing you to replace more f'n components in the ac system.

Thanks a lot for these ideas, Pierremcalpine! I think that my maintenance budget defintitely prefers the sound of option 1 more than 2 !
You and Bobthecabbage have convinced me to get under the front end of the car this weekend and shine a torch on the compressor clutch to see if I can see it engaging continuously (hopefully without removing a wheel!?) and I will also check the plug to see if corroded.

As for option 2 ! If the compressor needs replacing, I guess that means the refridgerant will need draining, and balancing and I don't rate myself as competent enough or tooled up enough for that - so it will be no air con or a cheap garage!

I will post again after inspection! If anyone can think of something else I could add to my check-list, I'd be very grateful!

Have a great evening, pierremcalpine!