W900 A-MODEL AC QUESTION? IF ANYONES FAMILIAR

Discussion in 'Kenworth Forum' started by flc120, Jul 5, 2015.

  1. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
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    wanted to know if anyone was familiar with the way the factory reddot under dash system works on these trucks? I noticed when I turn the ac on I hear a vent or door flap over when ac is engaged what is this?

    ive changed just about accomponenet on the truck and it seems as if the cold air is being divereted somewere else, when I first turn ac on in the middle of the day it blows out 100 degree air before starting to come down in temp soon.

    keys to what ive done

    heater system bypassed completely
    outside vent has been deleted it only sucks air in from the cab


    has new York compressor
    new replacement non grill denser condenser 20x30 large unit
    new drier
    both front and rear evaporators were cleaned up from dust,dirt and debris
    new hoses.

    truck will drip from front hose and rear sleeper hose the water as usual from evaporator core sweating.

    fan clutch has been wired for now to come on when ac is engaged.


    guage readings are as follows at idle 45 psi low side / 160psi high side WITH FAN ON if you cut the fan off low and high side both come up, high side will come up to 260psi.


    anyone here can help im going crazy
     
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  3. baha

    baha Road Train Member

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    Hot air is from eng. heat moving into firewall, Is the a/c comp. turning off for a short time to allow ice to melt, if not you are frez. up after a short time of running a/c in damp weather,the temp control is 2 wires near a/c box with a temp probe wire sticking into evap. will the doors move when you move levers to def. or floor then to dash, ck air or cable to each door then be sure they move free, you may be missing a hose under dash an cold air is just cooling back side of dash
     
    flc120 Thanks this.
  4. flc120

    flc120 Heavy Load Member

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    Miami,FL (yeah i know :( )
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    Well you can hear the doors switch over, when i cleaned evaporator coil i had to pull out blower motor so water would not mess up blower motor. i never felt anything open but you can hear noise of something clanking over, this truck pulls air from behind air cleaner on side of cab not from firewall, there are no firewall openings on a model kenworths. So weres that hit of hot air coming from if it sucks heat from inside cab.
     
  5. baha

    baha Road Train Member

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    CK the holes that A/C heater lines pass thru fire wall, some rubber sealer will seal them thats 7o mph wind thats trying to get in , find the tubes that blow ac into vents an look to be sure all are still conn.
     
  6. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
    Miami,FL (yeah i know :( )
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    Yup all are still connected, its just one large one goin to top of dash similar to 359 peterbilts. And those holes including the expansion valve holes are all sealed up with silicone, i did that whem i first bought it
     
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  7. baha

    baha Road Train Member

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    --You can pull ft. cover off A/C box and double ck. if flaps are closeing instead of opening when you hear the flap moving when you turn on power?
     
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  8. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
    Miami,FL (yeah i know :( )
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    well after taking apart the HVAC box again I think I found my issue, turns out not to long ago I had lost low and middle blower speed on the switch, one day I had remembered I turned it to the middle postion and fan stopped blowing and smoke started coming from vents I paid no mind to it and stopped using any speed other then high.

    well I started looking around checking to see if the flapper door on inside of box was opening and I had to pull blower motor out and reach and feel inside of box but when I did this I was surprised by burning the side of my hand pretty well with you wouldn't have guessed it a FIRE RED HOT blower resistor spring I BURNED the skin off my hand from how hot it was. well I looked inside of box to see that resistor was GLOWING FIRE RED while blower motor was spinning, so I disconnected pigtal going to the resistor itself which runs fan in default HIGH SPEED when there is no resistor present connected and sealed everything back up and now with a digital temp gun I got vent temp down to 38 degrees im thinking its working now for sure.

    turns out when I put digital temp gun pointed at the glowing red resistor it picked up a temp of 200degrees when it was glowing red. so my non cooling issue was a 200 degree fireball in the air vent track with ac on NO WONDER..... WOW...

    NOW heres my question is should I change both blower motor speed switch and resistor? im guessing maybe the blower speed switch is shorted inside?

    also this system supposedly holds 3lbs max Freon and I had put 3lbs in it but in trying to diagnose this problem I added on more can of Freon which would be like 3.25" lbs or a bit more should I pull Freon out of system or should I just leave it the way it is?
     
    baha Thanks this.
  9. baha

    baha Road Train Member

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    Just put a new resistor in an it should work on all speeds, not enough extra gas to let off the extra now, you will have to put on a long sleeve shirt now to keep from being to cold on hiway.
     
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