ABC's of 80's Cooling Part III - Press Switch (1 Viewer)

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Part III - Pressure Switch Activation of Aux Fan for better A/C Condenser Cooling.

In Part II, you will find the relay trigger options for wiring the pusher Aux fan for maximizing A/C condenser efficiency. In Part III, I will detail the procedure for wiring the Aux Fan to come on using the A/C Condenser Pressure switch. Luckily for the Toyota purists this uses only 10 dollars worth of Toyota Parts.

By now, you should have the Aux pusher Fan mounted in front of the A/C condenser, a relay mounted, and your Battery Feed (with appropriate Fan Fuse please!) to pin 30, and the Fan Positive Wire to Pin 87, Fan negative wire grounded to chassis. You can hook pin 85 (12+ relay trigger - low amp) to either switched power or directly to battery power (what I prefer for after-run). That should leave only Pin 86 (relay activation ground) not connected.
rinthe Aux Fan for Maximum Performance
To recap Part I& II I identified the need for some low rpm/low vehicle speed condenser cooling, and installed an aux fan. Now for fan activation... Most folks that have done this modification have tapped into the compressor 12v+ line. The problem I see with that is when the A/C compressor is shut off from an overheat situation (108C - 226F engine temps) you also lose the aux fan cooling when you need it the most. It can also lead to a massive drop in idle rpm (stall even), since you are adding compressor *and* fan amp load at the same instant. Thankfully Toyota made the solution cheap and easy. There is an unused pressure circuit already in the A/C high pressure switch.

When I replaced my factory hi/lo pressure switch 886450-01080, I noticed both the old and new had 4 pins, and the plug only had 2 wires. The FSM lists 2 pressure circuits for this switch: Hi/low in series, and a Medium Pressure switch. But, they only use the hi and the lo series circuit, which leaves a great Factory aux fan activation circuit ready to install.

The Pressure Switch works as follows:
Hi Pressure circuit - off - no continuity = 412psi (A/C Compressor off)(Aux Fan = on)
Hi pressure circuit - on - continuity = 327psi (A/C Compressor on)(Aux Fan = on)
Lo pressure circuit - off - no continuity = 30psi (A/C Compressor off)(Aux Fan = off)
Lo pressure circuit - on - continuity= 33psi (A/C Compressor on)(Aux Fan = on)

MED pressure circuit - on - conitnuity = 192psi (Aux Fan on)
MED pressure circuit - off - no continuity = 156 (Aux Fan off)


continuity = completed circuit
no continuity = interrupted circuit

So, tapping aux fan relay ground into the unused medium pressure will allow aux fan activation at 192psi>. Which means exactly that if high pressure cutout switch is triggered, the fan is still running. It also means when A/C is switched off all together, the fan will drop the condenser down to 156psi, and shut off.

This also acts as an afterrun cooling circuit, since you can use battery power to the relay, not any other switched power. Run the truck to the store, shut it down, the fan runs until the high presssure is down to 156psi, then shuts off (10seconds - 3 minutes depending on how hot the condenser is). Come back out, start the truck, turn on the A/C, instant cold. Ok, now the skinny on the procedure for pin 86 routing (this is a ground circuit!)

1) You need only 2 parts from the dealer (mine had them in stock)
QTY 2 x 82998-12270 Terminal = 10.oo for the pair

These are 2 precrimped and short lead terminals with weather plugs attached that will plug into the unused Med pressure ports in the hi/low pressure switch plug at near the site glass.

2)Remove the switch plug. On the back you will see two wires going into the switch plug. On the 2 unused round holes you will see two black rubber plugs, remove those (I pushed them from the terminal side out the wire side with a small piece of wire), they are just pressed in.

2) Now from the back of the plug, you will insert the 2 leads into the holes in the plug. STOP. Make sure that the retaining clip divot (the indentation about half way down the silver terminal) is located to the ouside of the switch plug. That's where the retaining clips for the terminal is molded into the switch plug. Push these into the clip and make sure the orange water plug on the terminal is sealed into the back of the switch plug. Plug the switch plug back into the high pressure switch.

3) Since this is a ground circuit, the wires have no 'polarity'. Take one of the leads and attach it to pin 86 (activation ground) on the relay. Take the other lead and attach it to chassis ground.

4) For manual override, you can piggyback another wire to pin 86 to switch in cab, then to ground.

5) Done


This will activate the Aux Fan on A/C startup after the condenser has reached 192psi and will stay on until condenser pressure reaches 156psi (130F and 115F respectively)

I have been running mine with the afterrun feature to reduce the temps on shutdown, and the fan runs about 1-2min after engine turns off, then shuts off.

Next up - Getting heat out of under the hood

Scott Justusson
QSHIPQ Performance Tuning
Chicago
94 FZJ80 Supercharged
 
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landtank

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citadel said:
you mention pin 85 and 86... what does that mean? any pics? thanks! this is great info!!!


It's how the relay is marked, for whatever reason he's spread the info out over several threads so you have to search around to be able to follow what he's doing. A little confusing to say the least. It all sounds good but I haven't been able to follow it through and probably won't bother unless I think I want to do this at some point.
 

landtank

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citadel said:
got it.. is that a specific relay or are all relays marked as such?


Dfferent relay configurations are marked differently I think, but I'not sure. I think the one he is using is a standard 12v relay.
 
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landtank said:
It's how the relay is marked, for whatever reason he's spread the info out over several threads so you have to search around to be able to follow what he's doing. A little confusing to say the least. It all sounds good but I haven't been able to follow it through and probably won't bother unless I think I want to do this at some point.

3 parts actually. The first is identifying the need for aux cooling, the second is the options for wiring it, the third is what I consider the best wiring option. Since all three are long and quite technical in nature, I divided it into 3 parts, also allowing debate/discussion of each part. Print the three, you have reason, options and method, pricing and part numbers. Here I thought it was simple!

Standard four pin relays are identified in Part II. The pins on a standard 4 pin relay are labelled clearly.

Given the difficulty one might have in following 3 recent posts, maybe it might actually find it's way into the FAQ. Then those that want it all in one spot can have it. Or you can use the handy search engine, type in: "ABC's of 80's cooling", you get exactly 3 hits Part I, II and III. Print the first post in each thread.

Scott Justusson
 
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SUMO - You rock!

I have the aux fan as you do but I currrently have it running full time since 90% of my driving is city driving to and from work..

I like your setup - where is the pressure switch located?
Is it the sensor mounted behind the drivers side headlight?

Could I tap into my exisitng switch/ sensor without opening the A/C system?
 
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greauxpete said:
SUMO - You rock!

I have the aux fan as you do but I currrently have it running full time since 90% of my driving is city driving to and from work..

I like your setup - where is the pressure switch located?
Is it the sensor mounted behind the drivers side headlight?

Could I tap into my exisitng switch/ sensor without opening the A/C system?

This is a non invasive procedure, you are not pulling the pressure switch only the connector to it. You are NOT opening the A/C system.

The pressure switch is the only electrical connection in the A/C circuit. Yes, on 94> it is located in front of the battery on the Drivers side.

I'm working on getting pics up which will help.

Scott Justusson
 
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Pusher fan installed

Greeting,

Thanks to Sumotoy for his assistance with this mod. Vent temps are noticeably cooler at idle. Fan comes on when needed (usually withing 1 min. of startup) and stay on after shutdown anywhere from 20 seconds to 1 min as needed.

The incabin override switch enables fan to run without AC being on for added airflow when desired. Bulb of switch glows when swith is off in the automatic mode and when fan is running while in the override position.

Pusher fan I used was from a mazda and measures approx 12". This was sourced from a pick and pull boneyard and really pushes the air. Mounting was simple. I was able to use the existing bracket from the fan onto my horn bracket and the bottum mounting point to the cross member under the condensor with a spacer.

Steve
94' 160,000
condensor pusher fan 003.jpg
 
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any chance we can get some additional pictures? Especially of where to tap for power?
How do you tighten the zip ties?
 
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stlcruiser said:
The incabin override switch enables fan to run without AC being on for added airflow when desired. Bulb of switch glows when swith is off in the automatic mode and when fan is running while in the override position.

Hi Steve!
Please post pics of this switch and some details on how you wired it. I'm thinking this might be a future mod.

Thanks to Scott for the research on using this pressure switch.

(BTW, I like those battery terminal covers in the above pics. :D)

-B-
 
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SUMOTOY said:
This will activate the Aux Fan on A/C startup after the condenser has reached 192psi and will stay on until condenser pressure reaches 156psi (130F and 115F respectively)


I have been running mine with the afterrun feature to reduce the temps on shutdown, and the fan runs about 1-2min after engine turns off, then shuts off.

It is about 95F today, my truck has been parked for 3 hours, and my condenser temperature measured with Raytek IR thermometer is 127F. I would hate to see the aux fan running for 3 hours or longer (if the battery allows that) after shut down. Am I reading this right, the fan will run until the condenser temperature is lowered to 115F? For those who is running this setup, what is your normal daily HIGH temperature?
 
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SUMOTOY said:
When I replaced my factory hi/lo pressure switch 886450-01080, I noticed both the old and new had 4 pins, and the plug only had 2 wires. The FSM lists 2 pressure circuits for this switch: Hi/low in series, and a Medium Pressure switch. But, they only use the hi and the lo series circuit, which leaves a great Factory aux fan activation circuit ready to install.

Nice find,

Just got out a mirror an indeed there are 4 pins on the switch, neither the FSM nor EWD for my 96 make any mention of this third contact in the switch,


I wonder if this is where the condenser fan (CDS FAN) found in other markets gets its input from?
 
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Medtro - The fan would actively cool your condensor and get it to the shutoff temperature within a few minutes. Your test had zero air flow through the condensor, so of course it took a long time. Try the same test with a house fan blowing through it and note the difference. The aux fan will have greater airflow than a house fan and cool it much faster.
 
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Bruneti said:
Medtro - The fan would actively cool your condensor and get it to the shutoff temperature within a few minutes. Your test had zero air flow through the condensor, so of course it took a long time. Try the same test with a house fan blowing through it and note the difference. The aux fan will have greater airflow than a house fan and cool it much faster.

My main concern is on a 115F day which is what prompted me to check the temperature earlier, how often and long will the aux fan run with the engine shut off? I measured the condenser temperature from another truck that has been sitting for more than a week, the condenser temperature is 103F, 8F higher than ambient. I am trying to avoid draining the battery on a 115F day.
 
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medtro said:
It is about 95F today, my truck has been parked for 3 hours, and my condenser temperature measured with Raytek IR thermometer is 127F. I would hate to see the aux fan running for 3 hours or longer (if the battery allows that) after shut down. Am I reading this right, the fan will run until the condenser temperature is lowered to 115F? For those who is running this setup, what is your normal daily HIGH temperature?

Medtro:
The only way I could see this mod running forever is if the ambient temp is 116F.

I'm on several weeks with this mod in chicago, and even on the 105F days, it ran maybe 3 minutes max. What I've been seeing recently is about 30 second afterrun with temps 85-95F.

For the first couple days I ran around with the shop jump pak in the truck just in case. I'm at the point now, I just don't worry about it. You could also just make a manual shutdown, or have a switch for the relay 12v+ trigger that allows battery power switched one way and ignition power switched the other.

HTH

Scott Justusson
94 FZJ 80 Supercharged aux cooled/after run/ pressure switch mod
 
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Beowulf said:
Hi Steve!
Please post pics of this switch and some details on how you wired it. I'm thinking this might be a future mod.

Thanks to Scott for the research on using this pressure switch.

(BTW, I like those battery terminal covers in the above pics. :D)

-B-

I'll jump in here with the details of the problem Steve had in his ground switch, which I had the exact same problem with in my 4R using a toyota switch to run my Rally 2000's.

Mr. T. and most aftermarket use lighted switches that switch positive voltage, not negative or ground. That becomes a problem because the in-switch lights are usually LED's which can't be hooked up in reverse. A typical lighted switch works as follows

Pin 1 = 12v source (ignition/battery)
Pin 2 = 12v load (to relay or fan or lights, etc)
pin 3 = ground
Light = pin 2 > Pin 3

Down/off = Continuity Pin 2 + Pin 3
Up/On = Contiunity Pin 1 + Pin 2 (and pin 2 12v>bulb>Pin 3 ground)

The problem with a switch to ground=on a relay is because there are 2 grounds (no 12v+ lead). Normally folks will try to just change the ground (pin 3) to 12v+. As Steve found out, that doesn't work on LED switches because LED won't fire in reverse = there is a postive and negative on LED bulbs. You can reverse the LED leads and resolder to make pin 3 12v+ and pin 2 Ground. Or, as I suggested to Steve, the easiest method is to just use a incandescent bulb lighted switch, because unless there is a resistor on it, it is non polarized. Specifically, the incandescent switch can be either a ground or a positive relay trigger.

Sorry, no lo:banana: version here. Or you could just use the Summary: Make sure the lighted switch is *not* an LED type

Scott Justusson
 
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