6420 Air Conditioning AC Not Coming On
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Thread: 6420 Air Conditioning AC Not Coming On

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    6420 Air Conditioning AC Not Coming On

    The AC is not engaging on my 2005 6420. The tractor is new to me, and it wasn't working when I got it. So far I've done the following to diagnose... what should I be looking at next?

    -Tested the fuse; good.
    -Tested the relay; good.
    -Tested the switch for continuity in Winter and Summer mode; good.
    -Tested for voltage to the switch; 12 volts, good.
    -Manually fed 12 volts to the pump trigger wire; pump engages, good.
    -Tested the dual pressure switch; No continuity. Cannot find if this switch should be open or closed.
    -Placed a jumper in the wire harness connector for the pressure switch; No change.

    Thoughts on what to check next? I believe there are some temp sensors under the seat pedestal in the cab where the evaporator and heat exchanger are, but I haven't removed the seat and opened that up yet. Not certain how to test those.
    Last edited by paoutdoorsman; 04-02-2018 at 03:14 PM.

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    Sounds like there may be more than one problem. When you supplied 12 volts to the compressor did it cool? The pressure switch should have continuity if there is enough pressure in system to activate the switch(approx 30 psi). Did you check to see if there was any voltage at the connector for the pressure switch? Key on, blower on, temp control on cold, and A/C switch on should supply 12 volts to the pressure switch and from there should go to the compressor. If no voltage to connector at pressure switch, remove the seat and cover under seat to access the thermostat control. It is connected by a cable to the temp control knob on right console. The a/c rocker switch provides 12 volts to this thermostat control first before it goes to the pressure switch.
    BigJim55 and paoutdoorsman like this.

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    paoutdoorsman(04-02-2018), Zebrafive(04-03-2018)

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    Quote Originally Posted by jd110 View Post
    Sounds like there may be more than one problem. When you supplied 12 volts to the compressor did it cool? The pressure switch should have continuity if there is enough pressure in system to activate the switch(approx 30 psi). Did you check to see if there was any voltage at the connector for the pressure switch? Key on, blower on, temp control on cold, and A/C switch on should supply 12 volts to the pressure switch and from there should go to the compressor. If no voltage to connector at pressure switch, remove the seat and cover under seat to access the thermostat control. It is connected by a cable to the temp control knob on right console. The a/c rocker switch provides 12 volts to this thermostat control first before it goes to the pressure switch.
    I only left the pump run 10-15 seconds when I manually supplied 12 volts. Just wanted to prove the compressor clutch and switch were good.

    Thanks for the info on checking for voltage at the pressure switch. I did not know to check that, so I just went out and did it. Yes, there is 12 volts at the pressure switch with the key on, blower on, and AC switch in either winter or summer position. No voltage if I turn the blower off, or turn the AC switch off. I assume this means that the system pressure is too low or too high, or I have a defective pressure switch?

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    Check the pressure switches with no voltage on them. Set meter to read ohms and both switches should read closed or 0 ohms. If low pressure switch is open then its either bad or system low on charge, if high pressure switch reads open, then the switch is bad.

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    Quote Originally Posted by RAM2940 View Post
    Check the pressure switches with no voltage on them. Set meter to read ohms and both switches should read closed or 0 ohms. If low pressure switch is open then its either bad or system low on charge, if high pressure switch reads open, then the switch is bad.
    Thanks RAM2940. This system has a single pressure switch listed as a 'dual pressure' switch. It is a two wire switch, and when reading ohms, the switch tests open/no continuity.

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    Is there a port for checking system pressure/adding refrigerant?
    I've only dealt with cars and added the correct refrigerant until pressure was correct.
    J
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    Quote Originally Posted by Zebrafive View Post
    Is there a port for checking system pressure/adding refrigerant?
    I've only dealt with cars and added the correct refrigerant until pressure was correct.
    All tractor AC systems I've been around have had high & low pressure test ports.

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    Have you put a gage on the system to see if you have good pressure. What is the pressure at the low pressure port. With out seeing it, if its above 35psi when the tractor is cold/not running, i would suspect the pressure switch is bad. R134 pressure should run somewhat close to outside air temp.

    Is this the pressure switch, there is a tech area on this page that gives operating perameters

    https://www.malpasonline.co.uk/itm/A...-Switch/106639
    Last edited by RAM2940; 04-03-2018 at 02:29 PM.

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    Yes, I would say that is the switch. The OEM part # is AL168231. Those operating parameters are helpful - thanks! Seems my next step is to get a reading on pressure(s). I need to check and see if my home heating/cooling system gauges will connect to the tractors system to read the pressures.

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    My guess is your home AC gauge hoses will not have the correct quick disconnects for R134A.

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