2nd Gen Non-Engine/Transmission Making a Manual Switch for the A/C

[zman]

how about a relay??

Seems to me that you could install a relay that works off the fan power lead to power the AC switch. The fan is always on unless the vent selector is turned to "off". If you use a relay, then when the fan is on, the switch would be powered, but if the fan is off (selector turned to "off"), there would be no power to the AC switch.



The relay would be powered from the fan power lead. The other side of the relay would be placed in the (separate/new?) AC clutch power lead, just prior to the switch. Need to get a relay big enough to handle the AC compressor clutch amp draw.



Does this sound like it would work?? If so, it would solve the condensor freeze up problem and give you AC with any of the vent settings.



Steve

 

[DUNE RACER]

Tom, I have not comfirmed that grounding the green/white wire will trigger the AC, when I tested and followed the contatcts on the HVAC module it seemed to be how it engaged but there is also a weak + signal on the green wire when the key is on. (wish I had a wire diagram).



If this is in fact how it triggers then zmans idea of a relay is great. You could use the + output when the fan is on to close a relay allowing your new seperate AC switch to get its - signal and if your new AC switch was on it wuold pass the - signal on to the AC unit like stock and engage the AC compressor but only when the fan was on. Right? basically the same thing zman just said.



I think the AC compressor relay is somewhere else as the green/white wire comming off the HVAC controler is tiny (like 18g), if so, then the relay for the new switch could be tiny. (I really need to get a shop manual)



I think I'm still going to take the easy way and simply loop the green/white wire through a switch but I'll try to help if someone else wants full control.

 

[zman]

Zach,



I'll bet you are right about there being another relay that powers the compressor clutch. My guess is that that relay is powered from the signals sent from the vent selector switch. If that is the case, then it would probably be best to wire completely around that relay if you want to be able to have AC in any vent position. If you don't, then there is a chance that that other relay won't be closed when the vent selector is positioned in a non-AC position - preventing the AC clutch from getting any power.



I was thinking of running a completely separate fused circuit to the compressor clutch so I don't have to worry about the other relay. We definitely need some wiring diagrams...



Steve

 

[DUNE RACER]

I think I got it

Zman, I think I found an easy way to do this. I've been testing more on the fan board and found that everything is triggered by a - signal. The fan contacts get thier - source from the vent selector contacts as soon as its turned from 'off' to any other position. This confirms what I was guessing, the fan is on at least low speed anytime the vent control is on any position but off.



This being the case, you should simply be able to solder a jumper wire that uses the feed for the fan portion of the controler to your seperate switch and from there to the green wire contact, then disable the stock AC contact.



This should give you AC at any position with the protection of the circuit not being live until the vent controler is at any position but off and the the fan is energized. The whole board is controled by a - signal, the rotary knobs simply direct that signal to different pins to activate different functions.



This is a shot of the copper board, it pops apart easily. My red pen points to the spot where a jumper could be soldered on and run to a switch. The green pen points to the AC contact that you would solder the other switch jumper to. You would then disable the rest of the stock contact to prevent the AC from comming on until you switched it on.

It actually looks easy to to but I have a way of explaining stuff that would make tying your shoe hard if I was telling you how to do it. I'm going to do more testing on this and see how it works.

 

[zman]

Zach,



Under your latest scenario, do we still have to worry about the other relay that activates the compressor clutch? I'm thinking we need to wire around it since it probably gets its signal from the vent selector switch. If the selector isn't in an AC position, then no signal would be sent to the other relay and it would remain open.



Steve

 

[DUNE RACER]

Steve, to answer your question-no.



The green/white wire appears to be the trigger wire to what ever circuit cycles the AC compressor. I have been in the shop testing and grounding this wire makes the compressor cycle as normal.



I set up a mock of my idea with jumper wires and it works great. The AC compressor cycles as normal in ANY vent position EXCEPT OFF. This will only allow compressor operation when the vent selector is open to some position. When the vent selector is open the fan is automatically energized (unchanged from stock)



This mod can only be done inside the module since the contact that gives the fan its signal to run does not terminate outside the module, it simply runs between the vent selector and fan selector.

 

[zman]

Zach -



Sounds good to me! Great job on the research!



Now to figure out how or if I can mount a nice button switch in the lower right corner of the HVAC control panel. You have it apart, what do you think??? Any room to pull this off or am I going to have to look elsewhere to mount the switch?



Steve

 

[DUNE RACER]

Steve, you should have room if you don't have the heated mirrors. It looks like the switch assembly Dodge uses takes up a bunch of room if its present. I'm going to be looking for a nice switch also, the wrecking yard I called wanted an arm a leg and one nut for the assembly with the mirror switch in it. I went and measured the one in my wifes 4runner and its too big (3/4 X 1) so tomorrow I'm going to see what I can find.



If its a lighted switch you can get dash light power from inside the module, there is one copper rail for that. If you need a + source for a switch that lights up when pushed you will have to splice that somewhere else and run a wire in. You could use a molex plug or something from radio shack also if you need to remote mount the switch (factory heated mirrors) so you can still unplug everything like factory.

 

[Tom C]

Zach, Great job on the detective work!! I think you found the cure. . also... I have the service manuals. I know it has some schematics. I'll look tomarrow to see if it has one for the AC. If so i'll e-mail it to you.





Illflem, You bet I got hot feet Must be from pushing harder on the brake after installing the power mods really though, sometimes I like to have cold air just from the dash vents. with the current setup I cant do that.



I sometimes wonder why they take options off a truck.

i. e. :

1) on my '97 I could turn the radio down when it was off. so It would not be too loud when I turn it on.

2) on my '97 you had the same vent controls with AC on or off.

3) on my '97 you could push the radio button without the key in to display the time.



but then they add some new stuff.

i. e:

1) on my 2001 you can turn the dash lights to normal bright without turning the dome light on (there is a position in the switch between variable setting and dome setting. this is good for daytime driving with the lights on so you can see you clock and such)

2) of course the mongo drink tray

3) heated mirrors

 

[DUNE RACER]

Well after beating around the junkyards today I'm convinced its going to be harder to find a suitable switch than I thought. I found one nice one that pops into a square hole but its too big to mount on the HVAC panel, I got another from a toyota that would fit but it would be hard to mount and I'm not sure it will wire up yet.



I don't think the Dodge power mirror switch will work either because, if I remember right, its not an 'on-off' type, you push it and it runs a timed cycle for the mirrors then automatically shuts off.



Where have some of you guys mounted your switches, I don't see to many other locations that are convienient.



Does anyone have access to a wire diagram for a toyota truck? 1990 or up should do (they all use the same switch) I can't figure what all the pins do by testing.

 

[illflem]

The Toyota switches I've seen have 4 connections. They are positive, negative, dimmer light + circuit and the switched pole. If the AC control is indeed a ground path you may not be able to use the dimmer light function because you will have to trade what would be the + on a Toyota with the ground. The AC on light will still work though.

 

[azcummins]

Dune Racer-

You're right about the timer on the mirrors. They run for a while, then it turns off.

 

[Tom C]

I found my manual. here's one thing to think about.



per the manual: "the compressor clutch relay switches power to the compressor clutch coil when the PCM grounds the coil side of the relay. the PCM responds to inputs from the a/c heater control, the a/c low pressure switch, and the a/c high pressure switch".



it would seem if you hot wire the compressor on, with a switch it will not cycle propertly. But Steve's way with the jumper wire should work. just cant use power from outside the a/c heater control switch.



ps: my scanner broke . i'll see if I can get a friend to help.



pss: the a/c compressor relay is located in the PDC in the engine compartment.

 

[DUNE RACER]

Almost done finally

Well I finally figured out how to get my Toyota switch mounted in the HVAC module and sorted out the inputs. The Toyota switch will only illuminate properly if it switches a + signal so I had to use it to trigger a relay to connect my - signal from the fan to the green AC wire.



I have about 2 more hours to finish up saturday, it looks like its going to turn out good, I used a project box from radio shack for the relay and mounted it in the dash. Had I not used a fancy switch the realy and external wiring would not be necessary, the one I got lights up with the dash lights and has a green light when its pushed for AC.



I have not cut or spliced any wires to do this mod, if I wanted to go back to total stock I could grab a module from a junk yard, plug it in and be back to original in 10 minutes.



I'll post a picture when its all done

 

[DUNE RACER]

Done at last!

Its done and it works great!



The switch I used made my install complicated, if your switch only need dash lighting and the AC circuit to control its easy.



In the picture you can see the solder blobs, I simply dissassembeled the module, drilled a 1/16 hole through the copper rail and the plastic under it then poked my wires up and soldered them to the copper. You drill a hole in the side plastic for the wires to exit, put a plug on them then and put your AC switch where ever you want.



This will give you AC in ANY vent position, will still have the stock protection of no AC until the fan is running and will allow you to use the recirculating feature of the 'max AC' setting without getting cold air.





-(1)- The blob on the top rail is + for dash lighting



-(2)- The blob right above the blue knob is a -- ground for lighting



-(3)- The blob right to the left of the blue knob is the controlled -- ground source for your new AC switch (this must be soldered right where it is to miss the plastic cover)



-(4)- The blob to the lower left of the blue knob is the stock contact for the AC. (The wire needs to be soldered there to avoid the cover) Then you MUST make a 1/16 gap in the rail above the solder joint to stop the stock AC signal from making contact.

I cut and removed the rest of my contact but it would work better to leave the rail and simply disable it.



These are the basic function wires to make a conversion, if you need + power for an 'ON' light, you will have to import that source from somewhere else. (I used my extra switched fusebox)



If you use a switch with an 'ON' light be sure to ground it to the controled ground source used in #3 or the light will stay on when your vent controller is in the 'OFF position.



The hardest part of this was finding a good switch, and where to put it. If you have heated mirrors you will have to mount your new switch somewhere else in the dash.



Sorry the pics aren't to great, I don't know how to post big ones.

 

[DUNE RACER]

Heres a shot of the end result-

 

[illflem]

Great job Zach!!! Looks the way it should have stock.



Just a note to folks with pre-98 trucks, the AC fix is much easier, just follow the instructions here.

 

[azcummins]

thanks for all the help guys! Once it breaks above freezing here, I'll give it a try.



Yeah TDR!!!

 

[jgil104]

a/c switch modification for 2001.5

has any one come up with alighted swich and/or a set of instructions yet ifso would plz e-mail them to me

-- email address removed --

t/y

 

[rono]

Dune Racer, OUTSTANDING JOB. I wish I had the time to research and do things like this. I, like many others, have wanted to do this since I first got my truck. Toyota has done this for probably 20+ years and it is great. From what Toyota did you get your switch?



Thanks Again and I will be doing mine soon.



Ron