Thread: Air Con compressor - excessive load?

They all drag quite a bit of power. You should drive a Honda Jazz. Mine will hardly climb with the compressor going. BUT it shouldn't be all that noticable while cruising.

First thing to check is whether your condenser fans are working. If not this raises the head pressure at slow speed. Mine would not turn over on the starter until the belt slipped. The fans should be on the whole time the aircon is switched on, so get out and check both are working.

Regards Philip A

Originally Posted by Hobbes

When driving it's enough to absorb a lot of the engines flywheel effect

By any chance is the "Viscous fan" locked up when your running the A/C???

Mike

Thanks Phillip, Mike
Mmmm, the A/c is working fine - condenser fans normal. Viscous working as it should. Once in the cruise it's ok (load noticeable but not really excessive).

The other clue is as the revs drop through 2000>1500rpm with A/C on there’s a real rough patch. I’m sure this is engine not compressor – you can feel it on the intake manifold. It’s almost as though the engine is suddenly running lean.

I’d suspect that it may be the air bypass valve sticking, but that would make the revs flare and this works perfectly under other circumstances.

Does the ECU read an “on-load” signal from the A/C system that effects the fuelling map by any chance...??

Does the ECU read an “on-load” signal from the A/C system that effects the fuelling map by any chance...??

Yes the ECU knows when the compressor starts and just adds a number of steps to the stepper. AFAIK there is no effect on the fuelling map.

What you are feeling on the motor is injector shut off. The ECU reads the VSS and TPS on overrun and injectors are cutoff if VSS =moving, TPS= idle and revs are >1500. The injectors reinstate at circa 1500RPM.

Also the Stepper is increased by a number of steps as soon as VSS=moving.

It all seems pretty normal to me.

Regards Philip A

Originally Posted by PhilipA

Yes the ECU knows when the compressor starts and just adds a number of steps to the stepper. AFAIK there is no effect on the fuelling map.

What you are feeling on the motor is injector shut off. The ECU reads the VSS and TPS on overrun and injectors are cutoff if VSS =moving, TPS= idle and revs are >1500. The injectors reinstate at circa 1500RPM.

Also the Stepper is increased by a number of steps as soon as VSS=moving.

It all seems pretty normal to me.

Regards Philip A

Fixed!!!!!!! Oh so fixed!!!!

To recap: with the aircon on the vehicle was a real dog to drive - basically on the overrun the revs would plummet and there was a real rough spot between 2000>1500 rpm as (as Phillip noted) the injectors shut off. Sometimes the revs would drop so quickly it'd almost stall until the air bypass opened up to compensate.

Prior to importing the rangie in 1996 we got Alpinaire in the UK to fit an OE aircon
system. The only difference over the standard install was the loom and relay pack were situated under bonnet.

So yesterday I took the multimeter to the ECU plug and discovered that there was never a 12v input from the compressor relay to the load input on the ECU (pin 21) - that took 10 mins to slice in and guess what? - - no plummeting idle, no "dry" overrun, like driving a different vehicle!

Only took 16 years to figure out!

thanks

Great that you got it fixed. I am beginning to doubt the professionalism of UK mechanics afte rthe cracked gearbox case posting as well!!!
It should be much better now.

Regards Philip A