Does the engine compensate for AC pump load? - LotusTalk - The Lotus Cars Community
 
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post #1 of 12 (permalink) Old 04-12-2016, 05:41 AM Thread Starter
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Does the engine compensate for AC pump load?

Pretty simple question that I'm trying to figure out for wiring up the AC on my 2gr...

Is an engine theoretically supposed to compensate for the load of the AC compressor when it's kicked on? It did seem like the RPMs increased on the 2zz slightly when the ac button was pressed, but Im wondering how the engine knows to compensate...if it does that is... is it part of the tune???

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post #2 of 12 (permalink) Old 04-12-2016, 07:03 AM
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Whether electronic throttle (as in this case) or using an idle control solenoid, the ECU will open them up a little to allow more air to compensate for the extra load. As far as I know, the AFR doesn't change, and ignition timing will change because that is the primary idle control mechanism. Also, with the Elise the fans always kick on a half speed higher than they otherwise would with the AC off.


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post #3 of 12 (permalink) Old 04-12-2016, 09:42 AM Thread Starter
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Ok that's kind of what I figured, any idea how the engine knows to do it? I was thinking if there was a signal wire pin I could just feed a 12v signal from the AC for the 2gr ecu...?
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post #4 of 12 (permalink) Old 04-12-2016, 09:58 AM
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Originally Posted by wek120 View Post
Ok that's kind of what I figured, any idea how the engine knows to do it? I was thinking if there was a signal wire pin I could just feed a 12v signal from the AC for the 2gr ecu...?
There's definitely a signal for the Elise (two it looks like - AC request and compressor running), not sure about the Evora. I know it controls the fan speed this way, but I don't know if the idle controller takes this as an input, too. The idle controller constantly measures the error between target idle speed and actual idle speed. This error is sorta added over time (no idea of your background, but it takes the integral of the error), and then the throttle angle changes proportional to this value. This leads to a relatively slow response on purpose to keep the rpm from bouncing up and down too much, but it is fast enough to respond to changes in load (with electronic throttles you can crawl in just about any gear by letting the clutch out slow enough that the idle controller keeps the engine at the target). It easily could compensate for the AC this way (reactive) or by using the pin in the ECU to automatically offset the throttle a tad and then still use the closed-loop control to maintain idle speed.

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post #5 of 12 (permalink) Old 04-12-2016, 10:34 AM
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This applies to 2GR a/c swapped in Toyota cars - possibly it applies here:

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Originally Posted by mr220v
There is a trick to getting the 2gr compressors to work that was previously unknown. The wire for the A/C clutch is there. However there is a secondary valve that diverts pressure back to the low side of the AC system. So, the AC compressor will kick on, but the system won't build pressure.

In gouky's original swap, he simply took the compressor apart and welded the valve shut. You could still do this, however, there is an easier way now.

What you do is junction the wire for the pressure valve into the A/C clutch wire. So, when you turn your AC on, the clutch engages and the valve closes.
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post #6 of 12 (permalink) Old 04-12-2016, 12:55 PM Thread Starter
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Originally Posted by Merryfrankster View Post
This applies to 2GR a/c swapped in Toyota cars - possibly it applies here:
Yeah I actually found that, and that's what I was going to do to get it running (just need to figure out which wires it is... Any idea which ones the 'pressure valve' wires are?) But Im thinking more in terms of the engine.


What is AC request? Is that just the 12v signal going to the engine telling it that the ac is engaged...?


Yeah I figure itd be strong enough, I just didn't want to have it almost die every time it kicked on, then rev up a bit every time it went off.

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post #7 of 12 (permalink) Old 04-13-2016, 01:39 AM
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Originally Posted by wek120 View Post
Yeah I actually found that, and that's what I was going to do to get it running (just need to figure out which wires it is... Any idea which ones the 'pressure valve' wires are?) But Im thinking more in terms of the engine.


What is AC request? Is that just the 12v signal going to the engine telling it that the ac is engaged...?


Yeah I figure itd be strong enough, I just didn't want to have it almost die every time it kicked on, then rev up a bit every time it went off.
I haven't studied the wiring diagrams yet but my understanding of the theory of operation is this: ECU gets status through the body harness of a/c on/off switch and blower fan, possibly temperature sensor on evaporator or accumulator/drier or elsewhere, not sure. Commands A/c compressor through the engine harness. At idle, ECU raises RPM to a/c-on idle RPM (which is a settable variable in aftermarket ecu's like for example powerfc). At any load other than idle, I don't know what adjustment ECU makes to timing or fueling with a/c on.

2GR a/c compressor has two harness connectors. See image of mine below. Left connector clearly powers clutch. Right connector must be the one powering the low-side valve. Wire colors are different from harness to harness and I haven't found out what wire does what.

Another option is to use the 2zz compressor if you still have it. From what info I've read, but not yet validated, it's a straight bolt-on to the 2GR block, and then you might be able to use your car's 2zz a/c lines to the compressor with little or no modification, provided that they reach, which I think they should.

Anyway I'm very interested in this because in my location a/c is an absolute must have year-round, so I'm gonna have to figure it out too. I hope this is of some help to you, and sorry I don't have it all nailed down yet.
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post #8 of 12 (permalink) Old 04-13-2016, 04:21 AM Thread Starter
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Originally Posted by Merryfrankster View Post

Another option is to use the 2zz compressor if you still have it. From what info I've read, but not yet validated, it's a straight bolt-on to the 2GR block, and then you might be able to use your car's 2zz a/c lines to the compressor with little or no modification, provided that they reach, which I think they should.

Oh ok cool, did you do a 2gr swap? Yeah I thought of doing that but I'm not sure if the AC would work if the 2zz ECU if it isn't connected/engine running (like as in if it requires an RPM signal to allow it to kick on)...I could be wrong though.
That and the engine idle signal to the 2zz wouldn't do anything...

Option 1:
2zz ECU still connected to the body side harness
2zz ECU wired directly to the 2gr AC comp.
AC signal going to 2gr ECU for idle increase (this Id have to figure out)
Figure out how to trigger radiator fans from 2gr ecu...

Option 2:
2gr ECU and AC comp,
AC Clutch wired to lotus AC on button 12v
AC compressor solenoid/pressure switch wired to either the same 12v, (that or the more complicated way; wired to some kind of temperature control switch to switch the valve on and off according to temp)
Aftermarket Fan controller with AC override input

The first one would be better because it wouldn't involve going into the front and rewiring fans, and also would still compensate for speed, but the second one is much simpler... man who would've known AC and radiator fans would be such a pita

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post #9 of 12 (permalink) Old 04-13-2016, 05:00 AM Thread Starter
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Damn... So looking a bit more at the 2gr ECU wiring diagrams, it looks like the only thing the AC amplifier (aka ac controller) only uses CAN communication to signal the AC being engaged... (there is a chance I could be wrong but doesn't look like it).

That being said I cant think of any way of increasing the idle (by being signaled) for the 2gr short of some kind of CAN signal ....something.. I guess the only real way to do it then is let the engine compensate on its own...

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post #10 of 12 (permalink) Old 04-13-2016, 05:06 AM
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Damn... So looking a bit more at the 2gr ECU wiring diagrams, it looks like the only thing the AC amplifier (aka ac controller) only uses CAN communication to signal the AC being engaged... (there is a chance I could be wrong but doesn't look like it).



That being said I cant think of any way of increasing the idle (by being signaled) for the 2gr short of some kind of CAN signal ....something.. I guess the only real way to do it then is let the engine compensate on its own...

I'll use the closed loop idle control on my daily to keep from rolling back on hills (hold brake, slowly clutch out until it starts grabbing, release brake, use clutch to hold the car still not unlike an automatic transmission creep), so I'd be shocked if the V6 can't handle a little AC compressor. It'll probably shudder very briefly though, so giving the ECU advanced warning would aid in comfort and all, but I doubt it is critical


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post #11 of 12 (permalink) Old 04-13-2016, 06:29 AM Thread Starter
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Yeah that's exactly what I figured, basically want to avoid having it shudder, that's the ultimate goal. That and figure out some way of having it controlled that will shut off the fan once I get over a certain speed.... That or maybe a thermocouple in the AC radiator and have it kick on and off at a certain temp...

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post #12 of 12 (permalink) Old 04-13-2016, 12:00 PM Thread Starter
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Ok so FYI for anyone who is interested in the use of the 2gr compressor (namely for the 2gr swap)

Per 2007 ECU RAV4 wiring diagram... Wiring plugs on Doc page 318 and 319
http://mr2.bordeauxgroup.com/2007%20...ms%20(EWD).pdf

Magnetic clutch operation:
http://share.qclt.com/%E4%B8%B0%E7%9...m)/0420032.pdf

Lock Sensor which shows the two wires for the lock sensor in the clutch plug:
http://share.qclt.com/%E4%B8%B0%E7%9...m)/0420050.pdf

Solenoid
Toyota RAV4 Service Manual: Compressor solenoid circuit (2006/01- ) - Diagnostic trouble code chart (2006/01- ) - Air conditioning system (for manual air conditioning system) - Air conditioning


The solenoid function purpose: "In this circuit, the compressor receives a refrigerant compression demand signal from the air conditioning amplifier. Based on this signal, the compressor changes the degree of refrigerant compression" so basically it controls the actual flow of refrigerant either bypassing the pump or going through it. So if you wanted the AC full power youd wire 12v to keep it open whenever the AC clutch is going... on contrary youd wire it to cycle if you didn't need the AC pump to work as hard.

**The ideal thing to do would be to make a cycling circuit that would cycle the solenoid on and off according to the temp dial (so how far over to cold you put it) which would save gas if you only needed marginal ac to maintain temp...

A/C compressor Solenoid B23 :
brown 1- ground
grey 2 - 12v in

A/C pressure sensor A21: (not using)

A/C compressor magnetic clutch B47:
light green 1- Lock (clutch lock sensor, sends out volt signal to lock sensor?)
white /black 2- SG- (clutch lock sensor, receives switched signal from lock sensor?)
blue 3 - 12v in from mgt cntrl relay


SO That being the case I BELIEVE this would be the appropriate way to wire the 2gr AC compressor. (can anyone confirm?) :

Wire B47 magnetic clutch pin 1 to a thick switched 12v coming out of the/an AC relay
Magnetic clutch ground grounded through the mounting

Wire B23 compressor solenoid pin 1 to ground
Wire B23 compressor solenoid pin 2 to EITHER the same 12v from the AC relay, OR a homemade circuit that would cycle 12v based on temperature setting.


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Last edited by wek120; 04-13-2016 at 12:24 PM.
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