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What's needed to make air conditioner work with MS


richard93vogue

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Hi all,

I have not got my 1993 3.9 Rangie running nicely on MS2. What I would like to do now is to work out what needs doing for the megasquirt to be able to signal the A/C compressor to kick in and provide the cool air in the cabin that is so relished and needed in the Aussie summer! I understand that there's not much call for it in England but surely someone has managed to get it to work with an MS?

Any experiences or tips gratefully received.

Richard.

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I don't know a great deal about it but the 14cux was in the loop before I had megasquirt. Now I have ms and no 14cux I have no A/C. Are you suggesting I retro fit a button in the cab? To what do I hook it up? Can you give me a few more pointers on where and what to do?

Thanks.

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I suggest you look again, in detail, at the interconnection between the 14cux and the A/C.

While I have NO V8 or MS experience it is highly likely that the link was to 'tell' the engine that a notable load had just been connected, because the clutch on the A/C compressor had engaged, and the engine was now expected to turn the compressor, as well as maintain a reasonable tick-over speed.

Thus there was a need for engine fuelling to be increased, which is what the 14cux arranged.

As I say, I have no MS experience, but I'd be surprised if there wasn't already the facility to accept a signal telling the MS of a heavy electrical load likely to drag the engine speed down.

I suspect you may have an A/C fault separate to any MS issues. Clutch not operating, or low on refrigerant being the most common.

HTH

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I know little about the OEM ecu, but it probably reads the rmp signal from the engine, and engaged the clutch only when the engine was running, given the ECU already needed the rpm signal for the injectors and timing, it was very easy for the electronics engineers to use that same signal via an electonic relay arrangement (transistors, or power switch etc) to engage the A/C clutch.

You basically need a 12v electrical supply to run the A/C clutch, how you choose to wire it is up to you....

option 1) take the "engine live" supply from the key switch via a switch in the cab, (on and off) directly to the a/c clutch.

advantage :-> simple to do

disadvantage :-> not a good idea to forget the switch is left in the on position when you restart the engine as it has the potential to cause belt slip given the initial torque of the a/c compressor would be quite high, and it may (note: I've never tried this) mean that the engine does not start on the first key turn.... (hence why most a/c clutches only engage when the engine is running.

option 2) take a feed off the alternator then via a switch in the cab (on / off) (this one would need some guidance from others as I'm not 100% sure it would work and which feed you need to take as the alternator when running would provide a 12v secondary feed signal that is energised when the alternator (and therefore engine) is turning

advantage:-> clutch would only energise when the alternator is turning (bit of a caveat here, read the disadvantage below)

disadvantage :-> requires someone else to point out which feed on the alternator to use, ad the caveat is that when the alternator starts turning it generates 12v, but the point at which it generates enough current and voltage for the a/c compressor to run is probably very low as far as rpm is concerned, so if you turn the ignition key to start position and as the engine begins turning (given that you've left the a/c switch in the cab in the on position), the a/c clutch may engage when the engine gets to the point of a few hundred rpm, hence again it may not start on the first attempt

option 3) take the feed from the engine run key position (the one before ignition start / starter motor engage), this time run it to both a momentary on switch (push button) in the cab and a relay normally open contact, from the other relay contact (common), take the feed to the a/c clutch and back to one side of the relay coil, from that same side of the relay coil, run a wire back to the other side of the push button switch.

The other side of the relay coil is run to ground.

what you have basically created is a latching relay

So, when you turn the ignition key to the "engine run position", the momentary switch has a live feed, but the relay is not energised, and when you now turn the key to the start position, the engine will start normally, but the a/c clutch will not engage until you press the a/c clutch button. When you press the button, it will enable the relay which in turn will backfeed the other side of the momentary switch plug keep the relay enabled and also the a/c clutch enabled.

When you turn the engine off, the relay will drop out and the a/c compressor clutch will drop out too.

advantage -> no chance of starting the engine with the a/c clutch energised (unless you press the a/c button in the cab before starting the engine.... not recommended)

disadvantage -> little more complex in wiring as you need a relay (you may need one with option 2 above), and a push button switch in the cab (momentary on).

I would recommend the use of an electronic relay as they are very fast to react, and require very little current to operate, if you use a "standard" 12v relay if you press the button fast it may not latch "on" because the current drawn by the a/c compressor clutch and the relay at the same time will mean that the voltage and current available at the relay coil may not latch the relay on.

If you're interested in this option I'll get a piece of paper and sketch it out for you.

If I were doing it, it would be option 3.

electronic relay would be one of these:http://www.ebay.co.uk/itm/121183847014?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

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Hi David, Thinking about it I guess the only logical reason for connection to the computer would as you say, be to increase the idle RPMs under load. Makes sense. I'm sure that can be sorted with the MS.

Robertspark, thanks for your detailed response I like option 3 and would certainly appreciate a diagram! Although the more difficult of the options it rings true as the 'best bet' for what I'd like to do.

I'm off to order one of those relays from fleabay now....might take another month to get here from Hong Kong :unsure:

On a side note I suppose I ought to get the pressure in the system checked as well.

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sketch here: http://i947.photobucket.com/albums/ad320/rclandrover/DSC06945_zps2fb1ab65.jpg

that seller seems to have a warehouse in the UK so it takes about 7 days to arrive from Salford 2 class mail provided they are in stock in the UK I use them quite a lot but they can be slightly more expensive than direct from China or Hong Kong. Hong Kong seems to be the slowest at the moment at around 3w to 4w

I've shown a fuse on the sketch (between the ignition feed connection and the push button), should be denoted as 4A or less (as the solid state relay is only rated at 4A), it's probably best to feed the 12v into the old ECU wire for the compressor as I'm not sure it it runs via another relay as the ECU would not have output much current and I'm also not sure what current the clutch requires but 48W should be enough (4A x 12V = 48W)

You will also need a pushbutton switch too

Hope it helps.

Rob

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Oh dear I've had missed something ...... you won't be able to turn off the a/c until you swtch the engine off as the clutch won't disengage.....

give me a moment as you'll need a second push button switch and I'll update the sketch this evening. (life / wife calling)

Edit: need to find and study the wiring diagram upon reflection as what I've shown will work but it needs wiring to the old ecu a/c feed wire and not directly to the clutch. Just need to make sure that the a/c system remains controllable.

What you're basically doing with this circuit is providing a manual confirmation that the engine is running before enabling the compressor. Then control the ac via the normal knobs and controls

Hence need to study the vehicle wiring schematic

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No need to make it complicated at all. Just a simple on/off switch in the interior, you may even already have one to enable/disable the aircon in the stock system ;)

As said, the connection to the ECU is only there for signalling the extra load, but honestly, I doubt that's ever needed. You could make the switch only work when the engine is running (with the alternator feed for example), so you can't start with the compressor engaged.

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...... right I've had a chance to think, again the 3 options remain and as elbekko said above the simplist is option1 followed by option 2, the advantages and disadvantages of these I believe stand.

If you're set on option 3 (which is not that complicated to wire, just wire the relay output to the old ECU a/c output feed (and back to the (+) side of the relay and button. Don't wire it directly off to the compressor (any of the options) as your A/c will just get colder and colder..... no means to cycle the clutch on and off (dopy git I am....[school boy error!])

If you want to test the theory, grab the old ecu a/c out feed and connect a length of wire on it back to the (+) of the battery... then give it a go at starting it then try the same thing again by leaving the a/c settings on the coldest settings with the fan also switched on, still with the fly lead on... and give it a go at starting it.

You've basically wired up option one above and tested it in both scenarios with the compressor clutch enabled which would emulate you forgetting to turn the on/off switch off.

Option 2 and 3 can be tested by starting it without the fly lead connected, then connect it and the clutch should enable.

If you've got low gas pressure, that should be picked up by the pressure switch (hence not a good idea to wire the feed directly to the clutch as all these functions won't work...)

Hope this helps for you to choose an option that suits your capabilities and tools available.

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Hang on a sec... if the MS has idle speed control it will stabilise the idle speed with the extra load as a matter of course, so no need to worry on that count.

As for switching the AC compressor, have you looked at the circuit diagram for the system? There's a few cut-outs in the chain for high coolant temperature, high/low gas pressure, etc. and there's a difference on the diesel ones which don't have ECU control to the AC (might be handy, eh?) but you shouldn't need to add switches, relays, etc. to make it work. I'd put money on you just needing to either ground or put 12v on a wire that used to go to the ECU and you'll be sorted.

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Hang on a sec... if the MS has idle speed control it will stabilise the idle speed with the extra load as a matter of course, so no need to worry on that count.

As for switching the AC compressor, have you looked at the circuit diagram for the system? There's a few cut-outs in the chain for high coolant temperature, high/low gas pressure, etc. and there's a difference on the diesel ones which don't have ECU control to the AC (might be handy, eh?) but you shouldn't need to add switches, relays, etc. to make it work. I'd put money on you just needing to either ground or put 12v on a wire that used to go to the ECU and you'll be sorted.

Exactly, while the petrol ECM does control the compressor relay (at least on later RRC, don't have the wiring for the older one at hand), the diesel has the A/C completely independent and relies on the pressure switches in the system to turn the compressor on and off. Looking at the diagram (RAVE ETM page K2 3-6) it's not as simple as adding ground or 12V, but you need to take the A/C logic relay out of the loop and drive the compressor relay directly, like on the diesel.

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Owing to having responsibilities that take precedence over me being cool in the car, I've not done anything on this yet. I did draw a diagram on the back of an envelope somewhere (and now lost it) to try and make sense of the curcuit and the ECM's role in it all but time and work deadlines mean I'll probably not get back to it till the holidays! I appreciate the ideas coming out in discussion though!!!

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Aircon is also vital where I live. I got mine working on my '97 D1 no problem (MS1 install). Here are my notes from the install.

The aircon wiring depends on the Lucas ECU and stops working when you disconnect and remove the old ECU. There is an easy solution. Remove the yellow-black wire from the AC logic relay, and put it on pin 86 of the AC clutch relay. You won't need the AC logic relay or the fan timer unit any more.

In future I might configure one of the extra outputs from MS to an “engine is running” signal. Then wire that through the AC logic relay so that the AC clutch can only be engaged when the engine is running. (I never did this as it works fine. If I ever do change it I might make it an rpm>700 signal)

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"The aircon wiring depends on the Lucas ECU and stops working when you disconnect and remove the old ECU. There is an easy solution. Remove the yellow-black wire from the AC logic relay, and put it on pin 86 of the AC clutch relay. You won't need the AC logic relay or the fan timer unit any more."

Thank you for that information AG! It relates directly to a question I asked on another post about what "chores" the Lucas ECU has to perform, but no one seemed to understand my question at the time.

Is it possible to leave the Lucas ECU in place so that it works the air-conditioner for example, whilst Megasquirt runs the engine?

Cheers Charlie

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Indeed, you run MS to get rid of a nasty ECU, and then .... keep it?

Exactly! This is why I went to MS, to get rid of the nasty Lucas ECU!

I just noticed a typo in my original posting, it says that I have NOT got MS running well, SHOULD have read: I HAVE got MS 2 running well :blink:

AncientGeek, in your part of the Southern Hemisphere you understand my need for A/C! Thank you for your experience at making it work. I will hopefully have time this weekend to search the rangie for the relays you mention and do the rewiring.

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My reason for thinking of a rpm> 700 signal is if the idles dips, the aircon will turn off and raise the rpm. I have had problems going down a steep slope with a/c on and the engine stalls. I could also use that for the wide band as they do not like being on when the engine is not running. However I am loathe to remove my beautiful conformal coating to do more mods.

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  • 4 weeks later...

Ok, so problem solved. Car is 1993 Vogue SE V8

To recap, I installed MS2 and found that my Air con no longer worked. Research showed that the 14cux computer is in the wiring loop and provides a -VE trigger signal to the AC clutch relay when the motor is running AND a fan speed has been selected.

After some debate I worked out that all I needed was to provide the AC clutch relay with the negative -VE switching signal when the fan speed switch is activated.

Now the fan switch in the dash operates a +VE switching relay (a relay operated by applying 12v) and as I mentioned the AC Clutch is operated by a -VE switched relay (operated by applying a path to ground/earth)

A neat little trick that I found is that by adding another standard type 12v relay you can take the +VE 12v signal from the fan speed relay and convert it into a -VE signal to feed to the AC Clutch relay.

The image below should help. This shows the additional relay being fed to pin 86 from the fan relay and giving a -VE via pin 87 to the switching side of the clutch relay.

Viola! It works! As soon as I turn the fan on, the clutch also turns on.

pos2neg.gif

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