Defrost A/C Toggle Mod

So I purchased a 1999 Tacoma over the summer and was surprised the first time I kicked on the heat to defrost my windshield that the A/C compressor kicked on. Needless to say, I wanted to be able to run my defrost to clear my windshield without the A/C compressor on. So with the help of several others on this forum I have figured it out and it is not very complicated at all.

Remove your dash cover around your A/C control unit and once you can see behind the control unit you will see a connector clipped underneath the area behind your vent selector knob. Unclip and disconnect this connector and you are done! Below is a picture of the connector you need to unclip and disconnect. The connector was originally clipped in the hole to the left of it in the picture. I also included a picture from the wiring diagram of the truck, just to show you what exactly you are disconnecting.

 

You want to use defrost to clear your windshield and chose to disconnect a component that helps your defroster clear your windshield. Sounds like tying a boat anchor to your bumper to get better mpg.

 

The beauty is that you can now choose if you want to use the AC. If you are having trouble defogging your windshield you would want to "toggle" the A/C on, but if you are just defrosting it there is no need to have the A/C running. Instead of having the A/C running no matter what, you can now decide yourself just by pushing the A/C button.

 

But why?

 

It's a cool write up but I too am failing to understand why you would want to do this.

 

I find it irritating when I want to throw a little air on the windshield and it's already cold outside and then the air conditioning comes on unnecessarily since the air coming in is already the right temperature. Same thing when cruising through rainy weather and all the windshield needs to stay clear is a hint of air running over it. I never use AC (alright there was this one time when it was 100+ at night and I felt like I was driving through hell) so having it turn on when I want to use the defrost is a pita sometimes. Sometimes it would be beneficial to have the AC come on to dry the air out. Then the AC button can be used to turn it on.

I guess it's kind of like the difference between manual transmission and auto or full auto and the kind where you can select the gears. Some people want more control. It's not something that bugged me enough to do anything about it, but now that someone asked and I saw how the circuit was wired, and now that there is nothing to lose, everything to gain, and I can go back to stock very easily, I think I'll try it.

 

The ac helps aid the defrosting.

 

I think the owner's manual says the A/C turns on during defrost to dehumidify the air. I think. It's been a long time since I read the manual....

 

In hot/humid times the AC will greatly help clear the fog or moisture from the inside of the windshield but, it can cause moisture to condense on the outside. Typically, this can be easily resolved by changing the AC to other vents or turning up the heat so not a big deal. However, in cold (subfreezing) times the AC slows and can even stop the defrosting process. Having the option is a plus in my book.

It's like asking why would you want to add the option of 2WD Low. Maybe not often but, sometimes it's better that way.

 

You could also just adjust the thermostat if you are cold. But glad you are happy.

 

Not trying to disprove it either... I just like to be able to choose if I want heat or dehumidified heat. I don't always want the heat blowing on me and set it on defrost so that I have heat but not on me. It is a personal preference.

If you do not like it just don't do it. You do not have to tell me that the A/C benefits me when I am trying to defog my windshield, because I know this and I can still hit the A/C button to turn it on manually if the need arises. This is simply because I enjoyed the defrost setting on my other truck for heat and did not need the compressor running 24/7 for no reason. I posted this incase there was anyone else also wanting to do this, without having to figure it out for themselves.

 

lol some people get it, some don't.

 

Blowing warm moist air onto a cold surface causes condensation. Hence the point of the AC drying the air.

But like I said previously, it's a cool mod. I just don't get it, but that's me.

 

Moving air removes far more energy from a system than stagnant air. Basic heat transfer. You can maximize this effect by cooling and dehumidifying the air, but it is not necessary.

 

If your windshield is icy in the morning, would you rather blow 55 degree air over it for 5 minutes or have the a/c on with the heater and it blow out 45 degree air?
It's going to DEFROST faster with warm air. This guy said he knows the a/c running helps with the windows fogging but he did this for defrost. Ice on the windshield. He also probably has a i4 and can feel the power difference with the compressor on.

 

I'd rather just scrap it and be done in 1 minute.

 

Basically its just preference for me... I made it this far without it and don't need it when I'm rolling down the road unless I it is very humid outside and my windshield fogs up. Once my cab is warm, I like to set it on defrost, low so that the heat isn't blowing directly on me but the chill stays away. I find it annoying when the windshield starts to fog up a little because of the air temp difference inside and out, so I kick on the defrost and my compressor kicks on. The A/C is not needed to clear a little condensation off my windshield. Yes I have a 4 banger so I feel it and since I can enable myself to choose, I choose to choose.

 

Heated cold air isn't going to have much moisture but your right, under the right set of conditions you could have moisture build up inside and running the AC would reduce that. We could discuss specific scenarios if you'd like. For example, I was driving home late one very cold night and there was blowing snow. My windshield kept freezing over and I would have to stop to scrape off the ice. After doing that a couple times I pulled the AC fuse. Then the windshield stayed warm enough to keep the ice from building up. In short AC doesn't always help. I could come up with other specific scenarios for disabling the automatic AC with defrost but I don't think that is necessary. I'm quite capable of pushing the AC button if I want the AC on... Anyway...

If I ever pull my dash apart I will leave that unplugged, thanks OP for the info!

 

Could care less good for u

 

I guess the term "defrost" is possibly complicating the discussion. My windshield is never frosted. I would scrape it too when I grew up in Maine @Madjik_Man, but now it's just to get the windows and windshield unfogged in the morning when the coastal fog comes in at night. The same thing can happen when I'm cruising on the freeway in the rain. I don't need cold air in these circumstances, just air moving across the windshield. In both cases I'd rather have warm air so it gets the cabin to the temperature I'm comfortable in, too.

I like what @ClevSix said about the 2 Lo analogy - it's not always the best / necessary choice, but at times it is a useful option.