17 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHAC Compressor/Engine Drag
Leading reported evidence
Check no leaks
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
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Discussions that performed work without a confirmed outcome
1
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Leading evidence: 'Check no leaks' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check ac turning resistance while free and engaged by switch' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed · Original poster
just not an AC guru, as this toy replaced a stage 4 120" harley, am learning but can notice little things like engine idle and surge but didn't even relate the AC to the problem before sending car in for a check up...
Check ac turning resistance while free and engaged by switch
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
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Read evidence and context
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Suggestion
You can take the belt off and check AC turning resistance while free and engaged by switch.
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Suggestion · Original poster
griffiths- will have a leak down check done on core
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
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Performed · outcome unconfirmed · Original poster
just not an AC guru, as this toy replaced a stage 4 120" harley, am learning but can notice little things like engine idle and surge but didn't even relate the AC to the problem before sending car in for a check up...
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
17 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T161109Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
New guy question....
AC unit on 2004 3.6 C2 has been diagnosed as being culprit on a intermittent surging. My question, "does the AC unit when not charged completely, actual create enough drag to notice decrease performance?"
Don't get me wrong was expecting to put a clutch in the car this week but when diagnosis came back thought it was a bit silly for me taking the car in...
The AC draws enough power to cause the tach to dip slightly when I'm at idle (at a light, for example) and the compressor kicks on.
I have never noticed any change in performance with the car moving.
My answer for your question: No, I don't believe so.
When you're trying to wring every last HP out - say, at the track - turning the AC off is a given, but in reality I don't think it makes a significant difference. There is some debate about whether driving with the windows down vs. driving with the AC affects fuel economy the most, which kind of gives you an idea of the performance cost of running the AC compressor...
Now, if the compressor is not working properly, it can be a huge parasitic drain. I believe there may be a thread on RL discussing the belt breaking from heat/friction caused by a seized AC compressor. However, this is definitely not the case for a properly operating compressor...
Seems that with a low charge level the compressor may be cycling on and off, mostly to protect itself from overheating and massive internal damage. Maybe that could be the intermittent surging you are referring to. Remember, the refrigerant charge also contains lubricants to lubricate the compressor. Who gave you the diagnoses? In other words, maybe they are right?
1) If the AC compressor was turned off (clutch not engaged), charged or not, the only drag would be 'very little', just the bearing in the compressor pulley.
2) If the AC was partially charged or fully charged and its clutch engaged, hp loss ranges from 3 to 10 hp depending upon the pressure in the high side of the system. As ambient outside temperatures rise the compressor high side pressure rises and requires more hp from the engine.
"Surging", if AC compressor related, might be the compressor clutch engaging and disengaging; which could be caused by a few issues.
If the car has a properly working AC and electrical charging system, then it shouldn't be that noticeable of a drag but I can see how if one and/or both systems are not working properly it could be very noticeable. Remember both electric cooling fans also come on and go to high speed when AC is turned on. You can take the belt off and check AC turning resistance while free and engaged by switch. Is the compressor noisy while running?
If the system is low on refrigerant, low enough there is not enough pressure engage the low pressure cut out switch, the compressor will not turn on and off, it remain off until its recharged properly; unless you have defective pressure cut out switch.
If you are low on refrigerant, you got a leak, find it and fix it.
With Boxsters and 996's, most common leak is the evaporator core.
Before the system gets to that point, it will cycle more frequently. This is headed towards the same direction as the dreaded water pump thread. Doc, please step in.
DBJoe996- New independent shop under recommendation gave diagnosis. Heck I'm having them vac and fill the system as a just in case....hate gremlins in my toys
griffiths- clutch was doing the engage and disengage dance so am leaning a bit more to the physical changes in the rpm are related
KrazyK- honestly haven't noticed any noise out of the car....IE need to do the faster mod or get a different set of cans....whole other topic not appropriate for today
griffiths- will have a leak down check done on core
no no on water pump, imsb, should i change my oil with ????? direction needed here lol
just not an AC guru, as this toy replaced a stage 4 120" harley, am learning but can notice little things like engine idle and surge but didn't even relate the AC to the problem before sending car in for a check up...
Compressor still kicks in even when you're just using the heater. And with the colder weather you often need the heater to clear up the windshield when it starts to fog.
Monitoring engine load -- via an OBD2 code reader/data viewer/logger connected to my car's OBD2 port -- and when the A/C is turned on maybe the load goes up from say 3.0. to 3.2. This is in precent so the idle load in HP is 6.5hp and it goes up to 7.16hp.
If the A/C doesn't have to work very hard if the cabin is at temperature already the A/C hardly draws enough power to register.
Load on the compressor, comp clutch is engaged,
is all relative to compressor pressures on a fix displacement compressor (variable compressors are different). The compressor pressure is not relative to cockpit temperature, its related to ambient air temperature; as outside air temps rise the pressure rises.
If the 996/997 system turns on the compressor based on either cockpit temp, evaporator core temp, or defrost function the load on the compressor will be relative to ambient air temp.
Ok ok, cars home, picked up 0730.
Everything situation normal.
AC system dye checked no leaks. It had the original caps still in place. They did a evac and fill job.
Compressor is not "dancing" and when operating under normal driving surge is gone.
Did do a plug replacement on all 6 so have to say it's a 50/50 as to the fix. Drove car med to heavy traffic getting out of Jax, then down to A1A to go home. No issues and am thinking it might have all been in my head....lol
Everyone has made great comments and will file those into my car knowledge once I finish absorbing the 10 CFR regulations I'm digesting for work...
Cheers to all and have a great finish to the week!
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