Have more control of your HVAC

Chris

Chris

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I found this article on Rubicon Owners Forum and though I would copy it here just incase anyone is interested.

As we all know the TJ HVAC selector automatically engages the AC compressor when the first three (AC) and last two (defrost) options are selected. Take control of the AC with just a SPST switch!

Here is what I did. On the back of the HVAC control there is a three pin connector on the far right with a black wire (ground), dark green (to fan speed control) and lightgreen (ground to PCM when AC or defrost is selected)... the light green one is the one we are headed for. Simply install a switch on that wire. Then YOU can control the AC.

I installed mine on normally open (NO) contacts.. When AC or defrost is selected I will push the button to engage the AC compressor. I did that because I rarely use the AC and I don't always want the AC to run in defrost. I can also use the bi-level select (third AC select) for heat without the compressor running.
Another option is connect normally closed (NC) contacts. AC compressor runs unless you deselect it. I would have done it this way in a high humidity climate where I used AC more.

I used a latching push button switch installed right on the HVAC control. The white and blue wires from my switch are my common and NO contacts. The others are for illumination I wired to the instrument lights and the NC contact not used. Any SPST switch can be used and put anywhere the user wants.

Most of these pics are of my switch install and have nothing to do with the actual intent of the mod. I was just pleased how well it turned out.

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What I have not confirmed after finding this article on ROF is what type of SPST switch is best for interrupting the light green ground wire...
 
glwood said:
What I have not confirmed after finding this article on ROF is what type of SPST switch is best for interrupting the light green ground wire...
Click to expand...

I’m no electronics guru, so if you do find out, I would like to know as well. This is one of those things I would like to do myself. It pisses me off how every time you turn the knob the AC engages. Such a design flaw IMHO.
 
It's not a design flaw... You want the ac compressor to engage in defrost. It will remove the humidity from the air, so you have less chance of digging the inside if the window. There is no good reason to not use the compressor...

If you think it's robbing you of power, remove it completely.
 
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Chris said:
I’m no electronics guru, so if you do find out, I would like to know as well. This is one of those things I would like to do myself. It pisses me off how every time you turn the knob the AC engages. Such a design flaw IMHO.
Click to expand...
I questioned the OP regarding what type of switch, and this was his response:

For push button switches....
Momentary is like your car horn. Contacts stay closed only while you hold it down.
Latching is, push it once, contacts close.. push it again, contacts open.... it changes state at every push.

You can get momentary if you want to drive around holding the button down to run the AC compressor
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A toggle with two contacts is a SPST and just opens and closes the two contacts.

NO=normally open NC=normally closed. The contacts of the switch. How the contacts are when the switch is in it's normal state, not engaged or selected.
Pretty much all SPST switches are NO.
I happened to buy a SPDT switch. Has both NC and NO contacts but I used only the NO. If I used NC the compressor would run unless I selected it and then the contacts would open. When I bought it I wasn't sure which way I was going to go.

There are lots of images if you google SPST or SPDT switches.

If you want it to engage the compressor when you select it but normally not be operating. Get a SPST latching push button switch. Or a SPST toggle.

Ranger_b0b said:
It's not a design flaw... You want the ac compressor to engage in defrost. It will remove the humidity from the air, so you have less chance of digging the inside if the window. There is no good reason to not use the compressor...
Click to expand...
On TJs there is. You may want bi-level dash and feet heat or fresh air without the compressor on. Almost every car made has that feature. TJs don't.
 
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Ranger_b0b said:
It's not a design flaw... You want the ac compressor to engage in defrost. It will remove the humidity from the air, so you have less chance of digging the inside if the window. There is no good reason to not use the compressor...

If you think it's robbing you of power, remove it completely.
Click to expand...

True, but on every new vehicle I’ve ever owned you have the option of turning on or off the AC compressor, even in defrost mode. I use my Subaru defrost all the time without the AC on, and most of the time it defrosts fine, even without the AC compressor on.
 
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So I just went to try this, but my wire colors are different. I have a black, blue with white stripe, and light blue with orange stripe. I'm going to guess it's the smaller blue with orange.
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glwood said:
That was quick! Good job picking the right wire. What switch did you use, and where did you get it, if you don't mind my asking...? I am supposing you simply interrupted that wire with the red switch?
Click to expand...
Yep, I just used a simple SPST switch to interrupt that wire. I bought a cheap 10 pack off of Amazon. https://www.amazon.ca/gp/product/B0171M3380/?tag=tjforum-20 They have tiny little terminals on the back, so I soldered the wires on. Stupid me should have taken more pics, lol.
 
I would want the switch to light up when the compressor is in the ON mode. The problem is switches that are LED lighted need a positive voltage to operate the polarity sensitive LED. Won't work with the 0v signal that goes to the PCM.
 
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well i went ahead and ordered the 12mm. Looks like that it will work. adding a couple of pics to the documentation. I am thinking of mounting it between the space of the fan and temp switch. vs the temp and selector switch. More support material back there and it is similar to how my tacoma was.

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Adding that getting the wiring out the back of the hvac panel is easier with the switch already having the soldered on leads vs a plug. A straight plug access hole from the back, would not allow this option to move on the other side of the temp control switch

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I did mine a little different. On my Jeeps I have attached a paddle switch down on the shifter that I can reach with my finger tips. It has many advantages. Like it was mentioned earlier, most vehicles have the option to kill compressor operation if desired.
I use mine to:
1. gain power when climbing a steep hill or passing, or merging onto the freeway on a short uphill ramp.
2. accelerating from a light in extreme high outside temps to give the cooling system a break, or when stuck idling for a while
3. when nearing my destination I like to shut the compressor off and let the fan run for a minute or 2 before I arrive, this helps 2 things, (a) it reduces "heat soak" when you shut down and (b) it allows the moisture on the evaporator to dry which reduces/eliminates the mold growth which can make the AC smell like dirty socks.
4. It lessens wear and tear on the rotary switch which you would be switching often to accomplish these things. I leave the AC switch on all summer and just switch the compressor and fan speed as needed.
I like the paddle switch as I don't have to fumble for a dash switch (especially while shifting) or take my eyes off the road.
Where I live we take our AC very seriously.

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Ya know, I thought about doing this as well, However, I wondered if I could use a non AC HVAC panel and have a button for control over the compressor … dump fisher price interior and poor controls. I had a 1999 Range Rover and the AC compressor was always on my default, you had to manually press and hold the “A/C OFF” to disable it.
 
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