M9000 A/C Electrical circuit elementary diagram/explanation.

[dvcochran]

My M9 has done very well this year. I did have to add a small can of Freon before 2nd cutting. I have noticed that randomly the air will start to get warm in the cab and I can look up to see the A/C light is Off. I can push the button off and then back on and everything is fine. It would be hard to test for continuity since it is overhead and a very random occurrence. I wondered if anyone had an elementary diagram instead of the line diagrams in the book to better understand the path.
Any suggestions on how to troubleshoot this is greatly appreciated.

 

[Dave_eng]

My M9 has done very well this year. I did have to add a small can of Freon before 2nd cutting. I have noticed that randomly the air will start to get warm in the cab and I can look up to see the A/C light is Off. I can push the button off and then back on and everything is fine. It would be hard to test for continuity since it is overhead and a very random occurrence. I wondered if anyone had an elementary diagram instead of the line diagrams in the book to better understand the path.
Any suggestions on how to troubleshoot this is greatly appreciated.

If you had to add refrigerant it is unlikely now that you have an electrical problem.

To start with M9000's can have one of three possible compressors and associated control wiring.

It is far more likely now that there is too much or too little refrigerant or air and safety switches are stopping the compressor because of destructive operating conditions. Turning the system off and then back on just allows the pressures to drop below the point where safeties are being tripped but you soon find yourself back in the unacceptable pressure range and the system stops again.

You risk damaging the AC system continuing to operate it in this fashion.

Best to get a qualified AC technician to leak test your system, fix any leaks and then recharge.

What book do you have..... the WSM has pretty good diagrams.

Dave

 

[dvcochran]

If you had to add refrigerant it is unlikely now that you have an electrical problem.

To start with M9000's can have one of three possible compressors and associated control wiring.

It is far more likely now that there is too much or too little refrigerant or air and safety switches are stopping the compressor because of destructive operating conditions. Turning the system off and then back on just allows the pressures to drop below the point where safeties are being tripped but you soon find yourself back in the unacceptable pressure range and the system stops again.

You risk damaging the AC system continuing to operate it in this fashion.

Best to get a qualified AC technician to leak test your system, fix any leaks and then recharge.

What book do you have..... the WSM has pretty good diagrams.

Dave

The tractor was already doing the switch/cycle thing before adding charge. That is the reason I even checked the charge and saw that it was on the low side per the pressures.
I added the charge on a day with a temperature of about 82-85 degrees. Per a 134a pressure chart the pressure should be 45-55psi low side and 225-250psi high side @85°. My final pressures were about 45 and 210. I did not have another can and did not want to over charge anyway.
Have you seen a M9 turn off for any other reason? The system has been cooling great all year.
FWIW, I had to do a total system replacement last year (all components). I added dye when I did the recharge and all looked good. Hopefully the extra charge was related to the initial repairs. If the charge gets low again and/or the system keeps dropping out I will have to pull the roof to look for dye/leaks but hopefully that can be avoided.

I have a WSM. I hate line diagrams, especially when they carry over to another page with poor identification, ala my WSM. I am an EE and am used to reading drawings and circuits. That is why I was asking about an elementary diagram so I could better understand the logic/current path.

 

[dochsml]

I agree with the other posts. Probably not an electrical problem. My tractor isn't fancy enough to have a cab and A/C, but I have plenty of vehicles with A/C that I've worked on. My guess is that you have a refrigerant leak somewhere (schrader valves are notorious for leaking) since you had to add some. There will be a low pressure switch on the suction side. If the charge is low, this switch will cut off the compressor clutch. Once the clutch is disengaged, the pressure in the system will start to balance again (low side pressure will rise) allowing this switch to be happy again. Then, if you turn it back on, the pressure will drop again since the charge is low. Rinse, lather, repeat until the leak and charge is rectified.

 

[SidecarFlip]

Sounds to me like a bad push switch or a loose plug on the backside of the panel which, BTW can only be accessed by removing the roof. If you do that. apply di-electric grease to ALL the connectors, Molex or not and clean the heat exchangers in the blower housing too. Remember, every other screw holds the roof on.

 

[dvcochran]

If you had to add refrigerant it is unlikely now that you have an electrical problem.

To start with M9000's can have one of three possible compressors and associated control wiring.

It is far more likely now that there is too much or too little refrigerant or air and safety switches are stopping the compressor because of destructive operating conditions. Turning the system off and then back on just allows the pressures to drop below the point where safeties are being tripped but you soon find yourself back in the unacceptable pressure range and the system stops again.

You risk damaging the AC system continuing to operate it in this fashion.

Best to get a qualified AC technician to leak test your system, fix any leaks and then recharge.

What book do you have..... the WSM has pretty good diagrams.

Dave

I hope to start troubleshooting this problem later this week. Taking the perspective that it is Not a Freon/pressure problem, where would you start? I will double check the pressures first. Can you say whether it should cut off on High pressure? It really seems to be cooling too well for too long but it is just a thought. I cleaned the evaporator last year and regularly blow out and flush the condenser. I have added an electric fan that cycles with the compressor. One simple test will be to see if the fan is running when the light is off.
I moved the tractor a couple days ago and the a/c would not come on at all for a few minutes then it started working. I hope to set down with the line diagrams and noodle out the physical path. If you do know where I could get an elementary diagram that would be great.

 

[dvcochran]

I got to work on the M9 today. It turned out the actual A/C pushbutton/blower speed switch was bad. I could jiggle the A/C button with my fingernail and it would come on/off. To my surprise my local dealer had one. $85 switch but fixed the problem.

 

[Dave_eng]

I got to work on the M9 today. It turned out the actual A/C pushbutton/blower speed switch was bad. I could jiggle the A/C button with my fingernail and it would come on/off. To my surprise my local dealer had one. $85 switch but fixed the problem.

Thanks for the update. Flip had suggested a switch problem.

Dave

 

[SidecarFlip]

I got to work on the M9 today. It turned out the actual A/C pushbutton/blower speed switch was bad. I could jiggle the A/C button with my fingernail and it would come on/off. To my surprise my local dealer had one. $85 switch but fixed the problem.

You do what I told you to do with the connectors?

 

[dvcochran]

You do what I told you to do with the connectors?

Yes, I sprayed them die-electric on the connector.
I plan add a manual shut-off on a heater hose. Do you know what size the hose is?

 

[SidecarFlip]

Yes, I sprayed them die-electric on the connector.
I plan add a manual shut-off on a heater hose. Do you know what size the hose is?

13mm id. 1/2" will do nicely. Put it under the bonnet on the fuel filter side. You only need to close one hose. Take your pick.

Actually, the heater cut on valve is pretty good (unlike the automotive ones). it's positive shutoff and electromechanical, not mechanical.

 

[dvcochran]

13mm id. 1/2" will do nicely. Put it under the bonnet on the fuel filter side. You only need to close one hose. Take your pick.

Actually, the heater cut on valve is pretty good (unlike the automotive ones). it's positive shutoff and electromechanical, not mechanical.

Agree, I do not believe I have a problem with it but better safe than sorry.

 

[SidecarFlip]

I could not feel any leakage past the valve when I had my roof off and I ran the motor up to operating temp. The hot side was hot and the other side was cold. Now my pickup truck was a different story and it got a shut off valve in the heater hose.