Unusual A/C issue.....PLEASE HELP!!!
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
Talked to a friend with HP Tuners and he stated look into System, theres a A/C turn off feature under RPM, he is betting the original turner forgot a zero so instead of it being 7XXX, its 7XX, so when you hit idle, pcm command ac off. This is used for WOT applications
He sent me this following my post, he said get a screen shot of the Stall Protect and AC Torque settings and post it to HP tuners forums for help if nothing make sense
Engine Torque Model
The PCM uses a airflow, fuel and thermal efficiency and heat based model of torque.
AC Compressor Torque
The AC compressor places a large and variable load on the engine when engaged. The PCM has a complex model of AC Torque load including inertia effects and ramp in/out when the AC clutch first engages. The AC torque calculation is also used to calculate the Idle AC Airflow compensation for IAC/ETC control during idle.
AC Bump Torque
This is the transient model of AC torque load when the AC clutch engages and disengages.
Delivered Torque PWM
The delivered torque PWM is used in various applications. eg. for some Holden vehicles it is used to control the fuel pump voltage.
Stall Protect
He sent me this following my post, he said get a screen shot of the Stall Protect and AC Torque settings and post it to HP tuners forums for help if nothing make sense
Engine Torque Model
The PCM uses a airflow, fuel and thermal efficiency and heat based model of torque.
- Inertia Factor: This is an engine inertia factor that is used to estimate torque required to accelerate/decelerate the engine.
- Fuel Qc Factor: This is the constant used to represent the Heat Of Combustion (Qc) in the torque model.
- MBT Torque Filter: This is the filter coefficient used to filter the calculated Mean Best Torque (MBT).
- Transfer Case Ratio: Transfer case ratio used in 4WD applications to calculate torque values when in 4WD low range.
- Accessory Torque: This is the model of accessory torque load on the engine (excluding AC compressor when engaged).
- Friction Torque: This is the model of friction torque loss within the engine.
- Friction Torque Multiplier: This is a multiplier on the friction torque value at various oil temperatures.
AC Compressor Torque
The AC compressor places a large and variable load on the engine when engaged. The PCM has a complex model of AC Torque load including inertia effects and ramp in/out when the AC clutch first engages. The AC torque calculation is also used to calculate the Idle AC Airflow compensation for IAC/ETC control during idle.
- Torque vs. AC Pressure: This is the torque loss of the AC compressor versus AC Pressure.
- Torque vs. IAT: This is the increase in AC torque loss due to inlet air temperature.
- Inertia Torque: This is the model of inertia torque load for the AC clutch when it engages.
- On Hold Time: Time to hold Inertia Torque before ramp out begins when AC clutch first engages.
- Inertia Torque Airflow Ramp: This controls the ramp out rate of AC inertia torque once the On Hold Time expires.
- Off Hold Time: Time to hold AC torque before decaying to zero when AC clutch is disengaged.
- Torque Reduction: Maximum amount of torque reduction that the AC can request.
AC Bump Torque
This is the transient model of AC torque load when the AC clutch engages and disengages.
- Delay: Time delay between commanding the AC on and the compressor loading up the engine.
- Ramp In: Ramp in rate for AC Compressor torque.
- Ramp Out: Ramp out rate for AC Compressor torque.
- Duration Max: Maximum duration for transient torque model ramp out. After this time AC torque will be set to zero when AC disengages.
- Reset Limit: If AC torque loss delta is less than this the adaptive idle cells will be reset to zero.
- ETC% Max: Maximum amount of extra ETC throttle position the AC airflow can command.
- On Delay: Delay before retarding spark when the AC engages.
- Off Delay: Delay before retarding spark when the AC disengages.
- max Spark Retard: Maximum spark retard the AC transient can request.
- Spark Off Delay: Delay before ramping spark out when the AC disengages. After Off Hold Time expires.
Delivered Torque PWM
The delivered torque PWM is used in various applications. eg. for some Holden vehicles it is used to control the fuel pump voltage.
- Stall: commanded PWM % when stall protect is activated.
- Shift In Progress: commanded PWM % when a shift is in progress.
- Normal Minimum: Minimum allowed PWM %
- Minimum Factor: Factor used to calculate PWM minimum PWM %.
- Fail Condition: PWM % applied to when torque management failure conditions are detected.
Stall Protect
- Enable RPM: If RPM drops below this them Stall Protect PWM % will be commanded.
- Delta Gain: Used for calculating RPM derivative factor to determine if engine stall is likely.
- Disable Factor - Hi: If RPM derivative factor is above this multiplied by current Desired Idle RPM then stall protect will disable (if enabled).
- Disable Factor - Lo: If RPM derivative factor is below this multiplied by current Desired Idle RPM then stall protect will disable (if enabled).
On The Tree
Joined: Jul 2009
Posts: 151
Likes: 5
From: GA
Thank you VERY VERY much for helping out. Here's where I'm my own worst enemy. I don't know how to do any of what youve stated!!! I'm good with mechanics, but dont know much about how to do any of what you suggested. Hell, I dont even know how to save your suggestions, save this thread, or post pictures to the forums I'm on. I'm close to 70 years old, and it's hard to learn this stuff. When I do, it's hard to retain it. Waaah, waah, wah!!! I know it does no good, and I hate admitting I don't know, but it's true. Anyway, the compressor does kick out at higher rpm, say 5,000, or thereabouts, under WOT. But maybe you've got it figured out. I'm pretty lost on tuning. Again, thank you for helping......
Would be nice if you could have the tune read by someone with HPTuners (preferably 4.8.7 or earlier) and then post it here.
Those of us with tuning knowledge could easily compare your tune with a stock 2000 tune file and see if the AC section as mentioned above, has been mucked with.
Those of us with tuning knowledge could easily compare your tune with a stock 2000 tune file and see if the AC section as mentioned above, has been mucked with.
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
Would be nice if you could have the tune read by someone with HPTuners (preferably 4.8.7 or earlier) and then post it here.
Those of us with tuning knowledge could easily compare your tune with a stock 2000 tune file and see if the AC section as mentioned above, has been mucked with.
Those of us with tuning knowledge could easily compare your tune with a stock 2000 tune file and see if the AC section as mentioned above, has been mucked with.
Grinder, only way we can help is to see the tune file. I’m 66, you ain’t that old.
PDX, yes a wot cutout. It’s in the tune also.
Without seeing his tune, and I’d bet something amiss there, very hard to say. My hpt cable won’t stretch beyond Portland…..
PDX, yes a wot cutout. It’s in the tune also.
Without seeing his tune, and I’d bet something amiss there, very hard to say. My hpt cable won’t stretch beyond Portland…..
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
TECH Junkie
Joined: May 2012
Posts: 3,048
Likes: 714
From: Poplarville, MS
Hey, Ron-Thats my line, lol. I’ve told some guys the same about my arms not reaching from Florida to Michigan, and vice versa!! Anyway, a guy on a different forum has found my original thread. Can't hurt to have another opinion. You have no idea how much I'd love to share that tune file with you guys. I'm sure I could get it from a guy I know with HPTuners. The problem is, how do I share it with you guys?? Do I take a pic of his laptop screen with my phone, then add the pic to a post? Or, do I have him print it out, and take a pic/pics of the printout page(s), then add to my post??? Thanks to ALL you guys for being so patient!!
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TECH Fanatic
Joined: Dec 2017
Posts: 1,467
Likes: 265
From: Bossier City, Louisiana
You have your HP Tuners guy save your tune file as "any name you want.HPT" - then copy it to a CD or a thumb drive, etc. Then attach it here. You should have a copy of this file saved off somewhere anyway as an insurance policy against PCM failure. That way, you can load your saved copy into a future PCM if you ever need it - hopefully not.
Rick
Rick
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
GREAT NEWS, for me!! I've found the original tuner. He is at a place called Motor City Speed, in Michigan. Made up of former Wheel to Wheel Powertrain employees. Name is Rich, works with Billy Briggs Racing Engines. Both in the same building. I'll check with him, and if he can't figure it out, I'll have him post the tune on here. Thanks a lot guys. I'm sure some of you will be interested just what the heck is going on here!!
TECH Junkie
Joined: May 2012
Posts: 3,048
Likes: 714
From: Poplarville, MS
GREAT NEWS, for me!! I've found the original tuner. He is at a place called Motor City Speed, in Michigan. Made up of former Wheel to Wheel Powertrain employees. Name is Rich, works with Billy Briggs Racing Engines. Both in the same building. I'll check with him, and if he can't figure it out, I'll have him post the tune on here. Thanks a lot guys. I'm sure some of you will be interested just what the heck is going on here!!
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
Solution found!!! I know this is an older thread. But it has puzzled me, and many others for several years. SOLVED!! Turns out my 25% UD balancer, and idle rpm both are to blame. Simply put, the compressor wasn't spinning fast enough to make enough system pressure to satisfy the PCM that all was good in the HVAC system. The PCM didnt detect enough pressure in the system for the compressor to stay engaged. PCM thought it was low on 134a, and disengaged the compressor. My tuner is really good, and due to that fact, he is able to set idle rpm lower than some tuners may be able to. Combine lower idle RPM with a 25% slower system rpm, and it would cut out. Simple in hindsight, not so easy in real time. I switched to a somewhat more aggressive cam this time, and the tuner raised the RPM slightly, now around 900 RPM. All good now!!!
Last edited by grinder11; Nov 11, 2025 at 03:29 PM.
