RPM surge problem when AC is on.
 

I have an A/C problem for my 2000/10 S40.I have erratic RPM whenever the A/C is switched on.Sometimes the RPM will even rav to around 300rpm by its own without pressing the accelerator pedal.During hot climate driving is even worse the car becomes jerky becos of the surge of the rpm and even lost of power.I had a few near miss at junctions becos the car just continue to move on after i release the accelerator pedal when driving,the car still moves forward becos the rpm stays at it's last position i.e 2500 rpm.immediately when i switch off the aircon the rpm goes back to normal.In the car i can hear hissing sound (like the gas being pumped)for about 5-10 secs always when the aircon is switched on and this symthoms repeats.No fault codes detected,Pollen filters,and idling valve changed,AC gas charged but still persist. What could be wrong?PLS Help!!!!! or ADVISE!!!!

Vollic

This sounds like a weird problem! Are you certain this fault is related only to turning the air con on, and nothing else? Can you rule out everything else and is it consistent?

Test to see if other engine loads cause a massive rise in engine revs. Sit there with the engine idling and try turning on lots of electrics and moving the steering wheel back and forth to put load on the engine (alternator and Power steering pump). Do the revs go up?

If not, when you turn on the air con do the revs go up like you say?

If so, what it might be is some fault with the ECU or whatever sensor (if there is one) is used to tell the ECU that the aircon is on. I do not know how it works on the S40 - but I'm sure someone else will come along and tell us.

a) Maybe the ECU knows the aircon is turned on from the climate control unit.
b) Maybe there is a separate switch which is activated.
c) Or maybe it doesn't know specifically and just adjusts the idle as necessary.

If a) or b) then the switch / ECU system could be faulty as it increases the idle way too high.

If c) I would expect similar symptoms from loading the engine in the way I describe above.

hi there i have the same promblem but this does when ever it feels like A/C makes no difference if on or off only had the car a week not happy but it goes back to the dealer to day (2001 s40) will let you now what they say, but i think its the electronis choke opening and closes there for let too much air in the system there for bring the revs up thats my gueses probaly wrong mind you any body else help would be much appreciated
thanks

tickover compensator
 

there is a electronic tickover compensator fitted, which automaticaly adjusts the tickover to the specified level to compensate for the extra load due to the air conditioning pump being used.
it could also be the idle adjustment valve which is sticking and needs cleaning with carburetor cleaner, though as you say it is connected to you switching on the air conditioning, i would go for the latter.

paul

took in to the dealers and they have no idea to take it back later and they said they would run it around for a couple of days to see what might be wrong:Dancing_chief: :confused_smile:

Yes it sound weird to me too.Yes,only when the AC is switched on and consistent.Its not so worst during cold seasons but still affects the driving performance.In summer (OMG) is worst.Sometimes the RPM will just rav once the AC is on even on stationary,need not to say during slow maneurve.Thats y i hate stopping at junctions or caught in a jam.The rav will just come and go and it repeats.When that happens is either i switch off the AC or select to AC button to off.The RPM will immediately goes back to normal.Driving on highway is much better becos the accelerator is depress on all the time so i don't feel the surge.
When i'm in the car i notice the RPM surges whenever the AC is switched on and the AC compressor comes on (a bong sound).It seems not normal to me as its sound loud followed by hissing sound for abt 5 to 10secs(sounds like flow of the gas pumped by the compressor).This symthoms repeats.
I did a test by tapping the accelarator after the bong sound when the AC is on,and the RPM will rise slowly and sometimes fast when the weather is hot to ard 3000rpm and stays there for abt 5secs or more or don't even return to normal.so i will have to switch off AC to get the normal rpm.
Will changing the thermostat and coolant sensors help?

I would suspect solely the fault is coming from the AC system,becos it happens only when using the AC.But just not sure the exact fault area.Worst still there is no fault code detected by Volvo Agent and got the idling vlv changed for nothing.Btw is the AC system somewhere link to thethrottle body?Means to say sending wierd signal to the throttle sytem causing it to have uncommanded throtle movement.
Where is the electronic tickover compensator fitted?Is it easy to change?How much will that be?

thanks for the reply!

I had EXACTLY the same problem with my 2001 S60. I had the ETM (electronic throttle module) cleaned out and it solved the problem completely. Could just be muck in the induction system.

Hi blue 60,
Mind sharing your experience.Where is the location of the ETM?Is it easily accessible and can DIY?
vollic