A/C issues

[PBJ]

Hey guys,
I went through the posts looking for a similar condition and found one with no help for the problem. Hopefully somebody has run into this before and could shed some light on it for me. I have a '00 Corvette that I did heads and cam on and everything is fine except when I turn the a/c on it turns right off. The system worked fine before the tune, I have to be missing something I just don't know what. There are several things that are very weird about it also....no matter where I set the target idle with the a/c on it will only go to 750 rpm. If I raise the rpm over 1000-1100 rpm the clutch will engage and the air works fine. The system is fully charged and the pressures are 32-35 and 180 +. When the a/c is cycling it is blowing 40 degree air. If I let the car come back to idle the the clutch will dissengage, the light will go out on the a/c head, but the car still has a load and draws the engine rpm down. If I turn off the a/c switch it pops right back up to the target 825 idle spec. I have taken the torque management out, put it back in, changed the timing at idle, air flow numbers, a/c bump....I am just out of ideas. Any help would be great.
Thanks in advance,
Joe

[WS6FirebirdTA00]

did you resolve this problem yet or no?

[CashDudeHomie]

Please help, I have this same problem on a 2000 pick up. The cam is messing with the IAC's causing the AC clutch to disengage at low RPM. What should I adjust to fix this?

[jimmyblue]

According to EC_Tune there is some sort of delta-RPM threshold
for idle, where if it's bouncing too much it will cut off the A/C
clutch. With a cam the motor is weak down low and the built in
torque vs airflow model is no longer good. So the airflow bump
that is meant to compensate the compressor drag, comes up
short and the engine RPM sags, putting you into cutout cycling.

If you supplement the A/C-engaged airflow (torque vs IAT vs
A/C pressure) too much you will get into a A/C-on cruise control
effect situation. So this (because it does not comprehend RPM,
so no idle-specific help there) is not too useful and you don't
want to mismodel the drag torque anyway; what we need is to
fix the torque-airflow model but that is buried.

One thing I can suggest to try, is the transient A/C torque
values; maybe if you comp the initial bump that would be enough
to get past the delta-RPM check. Try ratcheting it up and see
if somewhere you get satisfaction. If so, tell me what you did.
Torque Management >Engine Torque - Inertia Torque and its
ramp in/out.

There is also an A/C offset min/max, in/out of gear, which may
need to be widened out to let the IAC add as much air as the
A/C drag really needs. I'm not sure if the PCM tries to learn
A/C offset or not, you could jack up the min and see if that
props it up enough. This is in Idle Airflow.

[MNR-0]

Have you enabled any stall protect strategies?

[jimmyblue]

I have the "stall saver" RPM table populated, this is all I know of.
Any suggestions about that, is the compressor cycling coming
from the stall saver or are you meaning that stall saver will
help with it?

[1slowsilverado]

Besides the A/C clutch what else does the Stall Saver affect and how?

[MNR-0]

Stall saver implements full derivative control when it triggers. It can stuff around with return to idle if you get some dip into the nether regions, causing overfuelling.

I leave the stall saver unset, all zeroed out. The only stall saver strategy I use is the one under torque management, and set the RPM enable to 400. That way, my idle tune has a chance to do what it must before being blown out of the water by stall protect.

[jimmyblue]

I believe you hit the nail on the head, I backed down the stall
saver RPM to 300 and it is happy now at P/N idle and almost
OK in gear with the A/C. If it ever touches the stall saver RPM
it still goes nuts. But the lower the RPM, the less the odds.

I think idle should be tuned with stall saver zeroed. I was using
it as a crutch and never got rid of it again.

Thanks, Grant.

[jimmyblue]

Stall saver is definitely the root of the clutch cycling.
I have had it yo-yo only once today, the clutch stays
engaged but the RPM is unstable. I think this is still a
MAP-dimension VE table problem. But on restart it was
well behaved and did not yo-yo again. I think it's got
to bury itself rich one time to set it off.