View Full Version : air con and stalling

07-08-2013, 01:01 AM
i finally installed back my air condition... connected the wires to the power fc too, so it knows when it's on (i know from past cars that it does jack shit, but whatever) and the problem i have now is that when it's on, the rpm's drop from 1000 to 650-750, and if i drive around and stop, theres a case it might stall the engine. is there a way to adjust the idle for the air con? i was thinking of using an adjustable bypass valve like we used to do on toyotas and hook it up on an unused port on the manifold...

07-08-2013, 07:44 AM
One of the functions of the IACV (AAC) is to bump the idle up to compensate for AC. However, the compressor will still load your engine down a bot when engaged. You can try either cleaning the IACV or maybe adjusting the idle a hair w the AC on.

07-08-2013, 08:21 AM
well, the iacv is controlled by the ecu, so its probably the ecu that's not doing it's job properly... classic powerfc being a jackass. the iacv is clean as a whistle,and the idle is already at 1000 rpm when the ac is off...

07-08-2013, 12:22 PM
Could also be your compressor getting old bogging the engine down more than normal.

07-08-2013, 02:49 PM
Usually adjust the idle with everything on, A/C and headlights and electric fans etc...

And by adjust the idle, I mean, set the power FC a high idle setting (900rpm or more) and adjust the incoming air at the iacv manually with a screw driver. This way the power FC has added a significant amount of incoming air electronically so that not everything you need to idle the car is coming from the iacv's manual bypass.

Now, when you turn off all your electronics, the idle sky rockets. But the power FC will now have headroom to adjust the idle down. Cycle the electronics a few times over the course of 20 minutes to allow the power FC to "learn" (it really does) how much air to pull or add when you load the engine with the A/C.

Make sure that when the A/C kicks on, the power FC actually knows. it has a separate box for A/C Idle and a little light that indicates when it knows the A/C is on. Just remember if the power FC is maxed out airflow wise when you kick on the A/C, it will have nothing extra to give the iacv, although it depends on the actual iacv as some have a reserved specific amount of airflow that is added when the A/C kicks on iirc, plus or minus the usual power FC adjustment.

07-08-2013, 03:49 PM
i'll try that. when i started reading your post i remembered that i havent actually done the "startup procedure" on the fc, and this is the first time someone mentions this method that you say. i'll try it for sure.

also as mikester said i think that when i drive and turn on the ac it really bogs the car down, i mean, come on its a 2.0, i was driving starlet turbos before that didnt get this much drag from the AC...

i guess compressors can be serviced , right? oh well, i just installed this one and filled it up, ill leave that job for the winter.

07-08-2013, 04:27 PM
I am having the same exact problem, I don't have a power fc though. I haven't been able to figure it out. I am going to try bumping my idle up a bit, have it set at 800 now.

07-08-2013, 04:48 PM
someone told me that on the IACV theres another plug called the fast acting idle valve which is for these kind of loads, to bump up the revs... he showed me different valve than mine:

and told me i should check if this is connected... i dont think i have something like this (s14 zenki engine) but i'll poke around.

07-08-2013, 05:11 PM
My IACV only has two connections on it. Just replaced it not to long ago. Looks just like the one in that picture.

07-10-2013, 12:48 AM
checked the manual, its true that from the air con relay a wire goes to the fast iacv...im gonna check it out on the car soon


07-10-2013, 12:52 PM
right. when that blue/red wire gets 12v it should bring the idle up significantly, instantly. Its designed to counteract the load of the compressor turning on.

Sometimes the IACV is old or stuck and the function fails. I would test it. Manually run 12v signal to the iacv with the engine running to verify the idle comes up.
also, whoever wires the harness is responsible for making sure the wire is correctly connected.

07-10-2013, 02:37 PM
well the new harness was made by my electrician friend and me, and its the first SR20 we worked, so we're learning as we go along :D

07-10-2013, 04:24 PM
i discovered another thing today. the compressor is really bogging down the car... driving at the freeway this afternoon, i see water temp is 91C...that never happens while cruising. i turn off the AC and within 15 seconds, the water temp goes down to 85. the car was struggling with the AC... so, can the compressor be serviced?

07-10-2013, 08:32 PM
what engine. redtop notchtop what ecu number

also do you have the electric fan behind the clutch fan in front of the radiator? and what radiator.

07-11-2013, 12:12 AM
sr20det s14 zenki (blacktop) ecu 76 pin power fc
dual electric fans from another nissan (dont remember, but they're powerful) behind a driftworks radiator

07-11-2013, 10:53 AM
sr20det s14 zenki (blacktop) ecu 76 pin power fc
dual electric fans from another nissan (dont remember, but they're powerful) behind a driftworks radiator

Probably Altima fans (popular choice) or whatever other comparable Nissans are over there in Europe. Yes, the compressor clutch assembly can be rebuilt/serviced. In the event the compressor needs to be changed, be sure to annotate the part number to ensure proper fitment.

07-11-2013, 06:06 PM
sr20det s14 zenki (blacktop) ecu 76 pin power fc
dual electric fans from another nissan (dont remember, but they're powerful) behind a driftworks radiator

I would get a clutch fan / shroud to reduce the electrical load on the engine, that will help with the idle quality.

You can replace the A/C compressor for $100-$150. Sometimes when the compressor is about to fail the fuse will start to pop that control the a/c. It might be a 10amp fuse. You can install a 5amp or 3amp fuse just to see if it really is pulling massive current and pops easily as an early sign the compressor is failing.

09-15-2022, 10:43 AM
old thread, but here are my findings on the issue,

after installing a reman compressor, I ran into this issue: the IACV was not kicking in once I turned on the AC.

here are a few things to look into:

1. If it's a faulty unit, remove and replace IACV.

2. wiring is faulty need to find a break in the harness.. bridge and repair and reconnect.

3. connection is loose.. check and make sure it's connected correctly (this was my problem) I have a broken tab. i need to secure it so it does not come loose.

after you troubleshoot... run the ac, you should hear an even louder hissing sound kick in once the IACV valve gets a signal from the ECU. this should stabilize the engine. you should be good to go from here.

I hope this helps anyone trying to troubleshoot the issue.