have an ongoing issue.

for a while when i turn on air con OR heater only on heat, the revs drop below normal idle then flick back up. what i think is the condenser clicks on then about 3 seconds later it clicks off. today i had the air con re-charged and its still doing it.

i have done an alternater test and all volts/amps readings are normal.

the ONLY time they drop below what the should be is when i turn on the air con or put the heater on heat. i can have lots of things on i.e lights, cd player, fogs etc and the readings are normal.

strange though, if i have lots on, the readings are fine. if i have lots on plus air con or heater then revs drops etc. if i DONT have lots on and i DO have the air con or heater on, the revs drops etc.

method of deduction tells me the alternator is ok but something is causing too much of a voltage drain when either the air con or heater is out on.

i need to check the pins on the air con relay i think. does any1 know what each pin on that rekay should read so i can check with my voltometer?

does the fan come on when you turn on the ac? does it work fine while you are driving?

had a similar issue last week and it was the fan relay that was burnt (under the RHD headlamp). without the fan the pressure built up so high forcing the compressor to switch off

at first i thought the click was the fan clicking on then clicking off again. the clicking on and off must be the fan because both the air con and heater, when switched on, make the fan come on. im sure i can hear the fan on whilst either air con or heater is on and clicking on and off.

its annoying the sh't out of me lol

when im driving the only time i notice a problem is when the car slows and the revs drop...but instead of the revs sitting at normal idle level, with either air con or heater on, they keep dropping, cause a rumble, then flick back up again. if i stay stationery, the clicking on and off starts till i pull away again.

your fan relay cause makes sense. ill take a look under the bonnet tomorow. how can i test the fan relay? i have a voltmeter to check the pins if needed, or which other relay can i swap it with?

update,...

checked all fuses and relays and all fine. did another error code check and no codes.

am stumped.

sounds like normal operation to me, what your probably hearing is the air con compressor clutch clicking on and off, the radiator fan will be permantly on whist air con is switched on and cycling compressor on and off, the lowering of engine revs is due to extra load on the auxillary belt from the comressor dragging engine down, so no voltage issues invoilved

and compressor works when you have heater on high or low, unless switched off with button, even then it will work again when heater direction put to windscreen

also you say the revs dropping not noticable when other lights etc on, thats normal as you are already loading the engine with alternator then compressor kicks in .

it does sound like normal operation but when the revs drop, the car feels like it wants to stall....then the revs flick back up again.

other posts from other members ive read have found this sudden drop in revs not normal. one even found a short in a connection to or near the battery.

last year i had the air con on and didnt notice the sudden drop in revs. shouldnt the ecu or icv compensate for the increased load when either the ac or heater is on to adjust the idle level?

tbh i wish it wouldnt cause the revs to drop. when i measured the load and turned on the air con, the amount of volts/amps it dropped to was worrying.