Want to add AC switch to my 2000 sport

I have searched far and wide to see if this is something that has been done before. I'm sure it has, but either my search skills are not up to par, or nobody has posted their modification.

For me, I like control. I want things to work when I want them to work. I do not like the heater/ac controls on my cherokee sport. For example, why must I have the AC engaged when the defrost is selected? This may make sense in Tennessee or Maine, but in Wyoming - I can assure you the air is dry enough. I'm fighting a loosing battle with gas mileage as it is, and in the winter, this kills my wallet - and needlessly. I want to add a switch to engage and disengage my AC.

My first idea was to pull the controls from a grand cherokee that has the switch. It's ohhhh so close to fitting but not quite. So what about cannibalizing the parts from that whole assembly? Turns out that little ac switch is just formed into the potentiometer circuit for the hot/cold blend. I could unsolder the switch, but it's not really a stand alone solution that I was looking for.

On a side note, I now have the electronic climate control and the analogue climate controls from a grand cherokee (late '90s) if anyone is interested...

So, I'm going to add an aftermarket switch (or a better pulled switch from some random junked car that might catch my interest). My questions are thus:

Has anyone taken this project in before? If so, I kindly ask for your wisdom and experience. If not, I'll need to use a relay, as control of the AC compressor is high amperage and I'd rather not have that running into the dash. Would the way in which aftermarket fog lights are added work in this case? Does anyone have data on the current draw when the compressor kicks in? I imagine it's slightly less than the fuse for it, which is a 15a for the compressor clutch.

Also, what about taping into those fuse wires directly since they already power a relay, rather than taping into the actual power lines for the compressor?

I see adding a separate circuit as safer, but potentially adding unnecessary complications. I'm not worried about poping a fuse during testing, but I am worried about blowing the compressor.

Hopefully this isn't too out in left field here and I can generate some good discussion. My only request is that you don't try to dissuade me from this task. I want my control, and I shall have my control. Silly or not, it's what I want. Any constructive input is, as always, welcomed.

Thanks everyone!

If you only want to prevent the A/C from coming on with defrost, just tap into the low pressure sensor lines that signal the PCM.

Yep^ all you need to do is tap into the low pressure connector, it's just a two wire pressure switch, wire a toggle switch on one of the wires, flip it open and the compressor won't engage.

Is it really that simple? I hadn't thought of taping into the low or high pressure switch line at all, but that seems really easy. Just to make sure: whatever selection I have on the dash switch won't change, this will be a bypass switch for all dash selections. It won't turn it on when the dash selector doesn't have it normally on, but it will allow for an off selection when the dash control has it normally on - correct? And if I am understanding it correctly, that is exactly what I want.

Talked with a friend, and he brought up a point I hadn't thought of: if I put a switch inline with the LP switch for the ac, will the computer register a fault? I'd hate to have the computer go into a fault that must be hard reset to clear. I also don't know how dumb or smart the pcm is at this point in the system. Does it have a third sensor wire? I'll be checking this out momentarily.

His suggestions was to put the switch inline right after the dash control. Assuming the wire splits and sends one to the pcm and one to the compressor clutch, if I splice the switch before that split, no signal is sent the the pcm at all, and therefore no error situation would be generated, regardless of how smart or dumb the computer is.

Thoughts?

In don't think it will throw any codes, its just making the system think its low on refrigerante. You can test it by unplugging the low pressure switch and turn the a/c on and see if it throws a code.

I've unplugged the connector from the sensor since my AC doesn't work anyway. No faults thrown.

Good to know it doesn't throw a code.

So my question now is, why not splice from the wire that is already in the dash rather than run a two wires thru the firewall? Yes, I can piggyback along holes already there, but wouldn't it be quicker/easier/less complicated to splice the switch in right there?

So if I read this electrical schematic correctly:



... wire number 6 is the AC control. Which according to my picture above this post, is the small, bright green wire.

Anybody disagree?

Anybody see an issue with splicing a switch here rather than on the LP switch in the engine compartment?

You are over thinking it. Unplug the compressor. It's one wire right by the compressor. Problem solved.

No - not over thinking it. Your suggestion doesn't give me control. That just disables the AC entirely. I want to be able to run the defrost or the recirculate settings with AND without AC at my discretion. That is why I want a switch.

Again, its all about control.

DJTimyD said:

No - not over thinking it. Your suggestion doesn't give me control. That just disables the AC entirely. I want to be able to run the defrost or the recirculate settings with AND without AC at my discretion. That is why I want a switch.

Again, its all about control.

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Then instead of unplugging it, wire a switch in line there so you can turn the compressor on or off.

I don't think you'll see a change in mph from this, and if you do it will be minimal. How bad is your mileage? Something else is likely wrong

I did this. I don't have pictures, but I cut the AC enable wire that goes to the HVAC controls and added a double pole, double throw switch. The switch allows on, off, auto and the other side of the switch controls some indicator LEDs that are glued behind the picture of a fan on the HVAC front panel. The fan picture/icon glows red for AC off, purple for AC on, and no LED for AC auto. It is neat, but I don't know if I will bother on my next XJ. A cheap SPST switch interrupting the same wire would give you off/auto.

@islander: oh, there are many things wrong with the xj in regards to mileage, the main one being the brick shape. You're right, it's not gonna be much, but every little bit helps. Especially with the fact that I run the defroster probably 6 months out of the year, and maybe a dozen of those days I need the AC on to dry the air. Also running a switch from there isn't any better than the LP switch location - both in the engine compartment and would necessitate running a pair of wires thru the firewall. Also, the compressor line is high amps. So I'd need to wire up a relay like an aftermarket fog light kit uses. See OP.

@jeepingben: according to the wiring diagram (I didn't put the whole image up because I came across my service manual in less than 'honest' ways) if I have a third position that runs it straight to pin 1, or ground, that would force the AC on all the time regardless of what position selection I have. That would match your off/on/auto selection you referenced. The only advantage I see with that is it would allow me to run the AC while the position selection was set to "feet". Otherwise the bypass would allow control over all other positions. I can't imagine I'll have only hot feet and need to run the AC on just feet rather than bi-level. The advantage is that I can always change the switch out if I do need it from the simple spst to a dpdt.

As a test, I pulled wire number 6 from the connector, turned the jeep on and selected an AC position - and the compressor did not kick on. I belive this is confirmation that the bright green wire in the #6 spot in the connector is the wire I need to splice a switch into.

I've taken pictures along the way and I'll post up a how-to so in case there are other control freaks like me, they can see what I did.

On a side note, anyone know where I can get the 4 position switch panel that is under the heater control? I know they were in police models. I'd like to put my switch there.

Thanks everyone!

IslanderOffRoad said:

Then instead of unplugging it, wire a switch in line there so you can turn the compressor on or off.

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This. K.I.S.S.

@josh I believe even simpler would be to wire a switch in the wire that's already in the dash, rather than running pair of wires thru the firewall and rigging up a relay to handle switching a high amperage power line.

No, @jeepingben had the right idea. Quick, easy, super simple. Much better than trying to switch something that's in the engine compartment.

Thanks for your input, however.

DJTimyD said:

@islander: oh, there are many things wrong with the xj in regards to mileage, the main one being the brick shape. You're right, it's not gonna be much, but every little bit helps. Especially with the fact that I run the defroster probably 6 months out of the year, and maybe a dozen of those days I need the AC on to dry the air. Also running a switch from there isn't any better than the LP switch location - both in the engine compartment and would necessitate running a pair of wires thru the firewall. Also, the compressor line is high amps. So I'd need to wire up a relay like an aftermarket fog light kit uses. See OP.
e!

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If mileage is your main concern you're in the wrong vehicle.

Im confused on why you're opposed to every suggestion that will make this work. Running a wire is no big deal.

IslanderOffRoad said:

If mileage is your main concern you're in the wrong vehicle.

Im confused on why you're opposed to every suggestion that will make this work. Running a wire is no big deal.

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I cant say anything about the OP, but here in Colorado we have mountain passes that go over 12k feet.

The ever powerful i6 STRUGGLES at times due to the altitude, but there are many times where you need the defroster on to keep the windows from fogging up. Having the AC compressor kick on has a very noticeable power drain from the engine, and when its not needed it can be a bummer. Many times you do not need the AC to dry the air, but only the hot air blowing on the window.

The wiring would also be simpler if you could tap the wire right where you want the switch to go instead of running two wires from the front of the engine bay to the passenger compartment. Sure that is very easy to do, but it would be a much cleaner install if you could tap the wire right under the HVAC controls!


I also have a Tacoma, and there is a slight mod you can do to have this happen, and I use it almost every day. Long story short you remove the dial, remove a detent and the defroster runs without the AC compressor running:yelclap:

@Starboard M Thank you! - that's an excellent discussion as to how this impacts my gas millage. I live at 6k+ feet and regularly travel to 8-9k+ feet. I think this may be an area that flatlanders just aren't as familiar with on a regular basis.

@IslanderOffRoad Allow me to clarify to help eliminate your confusion: I am not opposed to every suggestion that will make this work. I even stated that @jeepingben had the right idea. There are several things I am opposed to: not doing this, unplugging the compressor/LP switch altogether, needlessly complicating this task. If I can do this without having to go into the engine compartment, wouldn't that be easier? Also, if I can do this and interrupt the signal before to goes to the computer, rather than interrupting the signal sent from the computer to the LP switch, wouldn't that be better? In the end, it comes down to control - which is what I stated my main concern was in my original post. Its not millage, but that is definitely an ancillary concern. When my jeep gets 15-19mpg, a change in one or two mpg has up to a 13% increase. I don't know about you, but I'd rather spend that extra money on upgrades and extras for my jeep, rather than burring it thru the tailpipe. There is already an excellent thread here on increasing gas millage, so I don't think that particular horse needs to be beaten anymore here.

Now, as to "running a wire is no big deal", see the picture below and notice how simple this was? Didn't have to run a [pair of] wire into the engine compartment or create a relay circuit to handle switching a high amperage connection. This is by no means the finished solution, but it'll work for now, until I find a better, more permanent switch and location.

Speaking of better, more permanent switches and locations, anybody have a bead on a 4 position switch bezel from a police package xj? I'd like to put this AC kill switch in there, and there is a company on eBay that produces various switches that drop into this bezel. I already have the 3 position one, and its full.

As always, thanks everyone for your suggestions!

DJTimyD said:

Speaking of better, more permanent switches and locations, anybody have a bead on a 4 position switch bezel from a police package xj?

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These are hard to find so do not be shocked by the price.

4897505AG

http://www.discontinuedspares.com/index.php?main_page=product_info&products_id=88407

http://www.oemautopartsandaccessori...herokee-2000/vtec/47886/pid/d223efcfd3d1e7ac/