Cold Aircon

[barcode Junior Member Find all posts View Profile Close barcode]

sorry i cannot post pic but am at work but attachment has a pic with how i think you mean to mount the bulb location. could you confirm if this is right

edit: didnt realise the pic would show - is the bulb in the same location as the red section?

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Turn your red mark clockwise so it is running along side the plastic straight bit, not sure if my arranged picture of yours will turn out but here goes


Where I have put the new red mark (not as neat as your drawing you obviously have a steady hand compared to me)

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

And put the black bulb part of the thermister say on the opposite side of the red mark, the side the green wire is showing in your pic, where your red mark starts is where I would start the green wire and have the black bulby part laying along where I have put my red line BUT on opposite side, then hold in place with two wraps of thin insulation tape then I put bit write on the very tip of the bulb (the sharp point of it) just to hold in place, dont put to much you wont fit it back through the hole....Hope this clears it up, next time I do anything Im going to take pictures incase anyone needs them lol..........Them Steve

[barcode Junior Member Find all posts View Profile Close barcode]

thanks for that. thats where mine is mounted now so guess will have to start tweaking the setup until i get a sweet spot. hope i find it soon as i dont have much patience with doing things too many times before i go thats enough.

[Offroader Member Find all posts View Profile Close Offroader]

Let us know how you go Barcode. Have you achieved a better result by moving the Thermistor?

[barcode Junior Member Find all posts View Profile Close barcode]

ok had a play yesterday. not sure if this is good or not but am finding am getting different results depending on when i test.
30 degree outside temp - if sitting still in neutral ac on and fan on speed 2 i get it to cycle between 2 and 8 degrees. however if i have been sitting still for a while - say 10 mins it starts to vary anywhere between -1.5 and 3 degrees and 8 to 9 degrees. hoping the minus degree isnt a bad thing
when driving on the freeway at 110 its the 2 and 8. if i turn car off for 10 and come back it cycles between -2 and 7 for about 10 mins before it gets back to its 2 and 8.
HOPE THIS IS MAKING SENSE
should i be worried about this or is it good to leave - the cold comin from the vent now is very cold. if the outside temp gets to 35 or more will this cause problems with how it is now.
i am down to about 1 min remove change position and refit now so mods can be done if need be to keep the system safe from doing damage if needed

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

That is not good, you are not getting enough airflow over the thermister hence the huge variance between cutting in and out. I checked myn again yesterday just for the hell of it and the vent on the left hand side of the say the radio is 6 and 7 1/2 and the drivers side is just under 7 and going to just under 8, the reason for the difference is the air is travelling that tad more so warms up a tad before coming out vent. For the trialing part of it I always have the recirc switched on so its circulating the air around thats already in the cabin. Sucking hot air from outside will make it work harder. I use to sit there and rev myn to 2 grand while trialing it, this is because the motor wont be reving enough especially on a stinking hot day, obviously the hotter the day the harder it works and the more heat the fan is trying to pull out through the condensor at the front of the radiator. My outside guage was showing 29 yesterday (think its out by 2d) had the fan on 3 and was just sitting there idling in my garage (wasnt reving it to 2g) and was just cutting in and out 6 and just under 8, not as good as my wifes yaris sedan at a constant 3 but better then the 9 and just over 11 I was getting, certainly makes a big difference just that couple of degrees. Yolu need more air flow and just double check your sight glass that the system is full as this will make the variance between when sitting still and cruising along or reving engine. You will probably see a few bubbles when it clicks in and out but should be clear while the compressor is in operatin, if white bubbly foam is flowing through you need a regas, dont forget if you have dual air then turn both on and check the system as well. Sounds like you have some more tweaking to do lol. Dont give up its worth having the nice cool air when needed, just a shame toyota didnt do more about it when people were complaining about there air not been real cold.............there response was its working fine thats the way they are........Cheers Steve

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

Guys
I have tried the mods to the thermistor as you guys have i.e moving the bulb away and also mounting it inside a pvc tube. I had my manual air gxl cycling around 6-8 deg C but I found on a long drive the compressor wasn't cycling correctly and the evaporator was freezing up resulting in no air flow from the hvac. I removed the thermistor and tested it under several temps as per the service manual just to check that it wasn't faulty. This led me to the idea of altering the resistance at certain temps to fudge the ecu into believing the evap temp was higher than it actually was. At 7 deg C the thermistor should have a resistance of around 4k ohm so I calculated if I add a 12k ohm resistor in parallel that would result in a total resistance of 3k ohm. That would result in the ecu "thinking" the evap was at about 20 deg C. Then I found in my collection of stuff in my shed a 100k ohm potentiometer, wired it in and mounted it in the handbook compartment in the glovebox and now I can dial in the outlet temp I want. Mine is set now to cycle between 1 and 3.5 deg C at fan speed 3 and high idle.

The pot is a jaycar item p/n RP8518 link $3.25 each.

Link to download excerpt from service manual




Good result? Any other info I can help with fire away. Btw I was struggling to get colder than 11-14 deg C before I started playing around with the thermistor!

Cheers

Ades

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Hi there Ades, very smart thinking there young man lol. The only thing thats got me thinking (doesnt happen often lol) if it was freezing up at 6 to 8d how come its not freezing up at 1 to 3.5 ?? Myn is like yours use to be, it was running at around 9 to 11 when I first bought it, now is 5/6 to 8 and back down again depending on what vent you stick the thermometer in, these temps I have put up here is tested from the passengers side of the radio vent (not the one closest to window). Is there any chance of zapping/killing any of the computer components by doing what you have done ?? Also are you willing to share yor wiring expertise to us ?? Cheers Steve

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

Steve
The trouble with the thermistor in the tube is it relies on the flow of chilled pressurised air from the hvac and that depends on the fan speed setting and the outlet settings. On a low speed setting I wasn't getting sufficient flow to chill the thermistor so the compressor ran too long and froze the evaporator.
Now with the pot mod, I am getting consistent cycling of the compressor at the pre set temp unless the ambient temps are too high and the compressor doesn't get the evap temp low enough to cycle (or freeze).

The potentiometer is easy to fit, remove the thermistor and bare ~1cm of insulation on the black wires near to the plug and solder a 30cm length of twin core wire to the two black wires - speaker wire will do. Then solder the other end to the pot - one wire to one of the outermost terminals and one to the centre terminal (pot has 3 terminals). What you end up with is the pot in parallel to the thermistor. I initially set the pot to 12k ohm and then installed it - I would advise this but you can trim up and down to adjust the outlet air temp you want. I haven't seen any adverse effects from going the the limits of the pot (0 ohm or 100k ohm) but it may throw a fault code (if the a/c ecu has the facility to) because theoretically going to 0 ohm is shorting the circuit. That shouldn't cause damage because the ecu would be protected from such a short.

As usual the standard disclaimer - I cannot be held responsible blah blah....


Ades

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Sounds extremely easy to wire up, think Ill leave the thermistor where it is (save me moving it around) and just pull the plug out the other end and wire in the two wires closest to the connection). So providing you dont turn the dial full clockwise or full anti clockwise you wont get to the zero or the 100 anyway in other words if the dial is some where in between your safe ?? I noticed the three termials so it doesnt matter which outer most terminal ?? as long as one wire goes to the centre conection and one either side of it ?? You say you set it initially at 12k ohm I presuming setting it is done by turning the dial is what your refering to ?? sorry for all the questions but im totally useless when it comes to these type of electronics so ohm's to me an 12k mean jack shit to my brain lol. Cheers Steve

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

If I were you Steve I'd place the thermistor back in it's holder inside the hvac. This way you know you are getting true temperature sensing and not relying on the airflow through the tube.
I'm guessing you don't own a multimeter? You could like you said set it in the midway position and adjust whilst the a/c is running watching the thermometer.
Yes one wire has to go to the centre terminal, think of the pot being a resistor connected to the two outer terminals and the centre one is wiped along the resistor by the spindle or dial - so the closer the centre one is to the end of the resistor the lower the resistance.

BTW take care with the holder, that part is no longer available. The thermistor is and they are about $20 trade (though ex Japan).

Ades

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Yeah mate i got rid of all the tubing and crap etc and its back in its holder just further down the holder so its not directly in front of the evap, only way I could achieve the temps im getting and cycling with about 1 1/2 to 2 degree variance so that part of it is all ok. Just incase you do need one, I bought a new holder when I did the mod as I tried heating it up with a heat gun and it went brittle and snapped on me, thought it was going to be a trip to the wreckers but rang toyota and they had to get one in from Japan, and the newer one was shorter so they obviously new it was an issue and tried to shorten the lenght of the holder so it didnt go inside evap as much but honestly didnt change a thing, I still had to pull the thermistor further back from the end of the holder and used insulation tape to hold in place. I do own a miultimeter (well I think it was supercheap one I bought 10 years ago lol) I have only ever used it for tracing 12V when fitting outlets and relays and things for driving lights, trailer plugs etc but never used for ohm's or anything else like that. I think you have solved the issue for everyone else with what you have achieved, has been pissing a few people off over the time, great going. Hopefully no one has any computer issues (doubt it very much) and all will be good.. cheers Steve

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Hey there Adrian, any issues since fitting the potentiometer ?? Going to do myn this weekend when I get a chance. Your still maintaining the same nice cold setting with any issues ?? Cheers Steve PS Will be up your way on sunday/monday...........

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Hi Adrian, sorry forgot to ask, I have speaker wire which I used for my home theater set up but is probably what I would class as heavy duty (probably triple the thickness of say the speaker wire in the car), I also have a spare wiring loom 7 core to suit a trailer so dont mind using a couple of strands from that ?? If not Ill just duck up and get a metre of standard speaker wire, What do you recomend ?? Cheers Steve