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!

[Mickey74]

Just remembered! A mechanic and entertaining Youtube volvo video repairs poster (called Robert!) suggests that, with age, the clutch position sometimes moves too far away from the solenoid and needs shims added to close the gap again and make it engage? Does this also sound plausible?? Has anyone done this job before? (Thanks!)

[pierremcalpine]

Originally Posted by Mickey74

Just remembered! A mechanic and entertaining Youtube volvo video repairs poster (called Robert!) suggests that, with age, the clutch position sometimes moves too far away from the solenoid and needs shims added to close the gap again and make it engage? Does this also sound plausible?? Has anyone done this job before? (Thanks!)

It's plausible. I tried it, didn't work. Don't bother trying with paperclips, they will fly right off. I ended up slipping a zip-tie under each "wing" and that seemed to get the right clearance. Still didn't make a difference in the end though. Here's a pic of how I placed them.


You may also want to purchase a set of feeler gauges to verify the spacing on the clutch. That will tell you whether you should even attempt to shim. Here's a link to one:
https://www.princessauto.com/en/deta...ge/A-p8729089e

Here's a helpful thread from a while back:
http://www.volvoforums.org.uk/showth...clutch+spacing

Note that there is no need to get under the car OR to remove a wheel to get a good look at the ac clutch. Just look straight down when at the front RHS of the engine bay. The clutch is the pulley that is the further down. You will be able to see it come on and off as the ac system turns on and off.

[Mickey74]

Thanks a lot for that again, pierremcalpine!
I will try this operation then only as a last ditch resort (if the clutch gap tests bad) before I give in to the pros!
Thanks also for the very clear photo of the very nice shim job!

You may also want to purchase a set of feeler gauges to verify the spacing on the clutch. That will tell you whether you should even attempt to shim.

I will definitely look @...

Note that there is no need to get under the car OR to remove a wheel to get a good look at the ac clutch.

Thanks also for this time saving advice...!

Have great afternoon!
mickey74

[Mickey74]

My volvo estate 2002 petrol v40 is working again !

Many thanks to Pierremcalpine and Bobthecabbage for your support (and anyone who thought about this!).

So here’s the very simple and free fix :

I turned my AC on 6 (full) and full heat to test if the engine would still surge (I expected this not to be the case, as I thought the problem was probably in the clutch or compressor as had been logically suggested). I was surprised when the engine surged and noticed that the compressor clutch was being engaged – I thought this could only occur when the compressor was needed to produce cold air !
I turned the engine off and repeated the procedure. This time the engine didn’t surge.
I then turned off the engine and on again, this time with the AC on 6 and Full cold.
There was no more engine revs surging ! I then tried to drive which had previously led to surging (as well as when idle) and there was no abnormal surging (hunting). The drive was as smooth as before… problem solved!

Cause? I don’t know, but it looks like the ECM might have been in a « stuck » state and simply turning on full heat then back to full cold (possibly in conjunction with turning the engine on and off) reset a stuck ECM. Please let me know if you have a more precise or different idea what caused this…I’d love to hear !

So before re-shimming, or removing an old AC clutch (my clutch gap is 0.63mm/ 0.025 imperial and still seems to work…), or replacing a compressor – try this simple fix first !

...me? I'm off to sit in a lovely cool car.
Mickey74