M9000 A/C Thermostatic Switch

[dvcochran]

I did a full replacement of all the major components on my M9000 last year. It does okay but not great. I had an A/C mechanic (not a Kubota specific mech)check it last week and he said the pressures are within range but something is causing the compressor to cycle on and off. The discharge temperature is about 56 degrees but not consistent.
In the parts diagram we see a pressure switch and the thermostatic switch (P/N t1065-72162) that goes into the evaporator. Does the thermostatic switch drop out the compressor when it senses a certain temperature? If so, does Where it is mounted inside the evaporator matter? Should it have any kind of insulation on the bulb?
I am wondering if it is being satisfied too soon. It is not a cheap switch so just swapping it would be an expensive gamble.

 

[Popgadget]

You could try jumping the pressure switch to keep it running, and then check the switch with an ohmmeter to see if it is cycling. Do the same with the thermostatic switch. Monitor pressures while doing this though in case there is something else going on.

 

[Dave_eng]

I did a full replacement of all the major components on my M9000 last year. It does okay but not great. I had an A/C mechanic (not a Kubota specific mech)check it last week and he said the pressures are within range but something is causing the compressor to cycle on and off. The discharge temperature is about 56 degrees but not consistent.
In the parts diagram we see a pressure switch and the thermostatic switch (P/N t1065-72162) that goes into the evaporator. Does the thermostatic switch drop out the compressor when it senses a certain temperature? If so, does Where it is mounted inside the evaporator matter? Should it have any kind of insulation on the bulb?
I am wondering if it is being satisfied too soon. It is not a cheap switch so just swapping it would be an expensive gamble.

My comments flow from my review of the WSM and assume the WSM covers your M9000. I have not studied the parts on line info.

More history would help.

What exactly was changed, who did the evacuation and how was the recharging done?

There are two different styles of compressor, Swash plate and scroll. The scroll has a higher output in terms of cooling. If you changed compressors, knowing which style you now have is useful.

Your system is unlike modern cars and pickups in that it has an expansion valve to control the temperature of the evaporator compared to a fixed orifice. The temp bulb of the expansion valve needs to be in contact with the evaporator outlet pipe. It is trying to keep the evaporator above freezing temperature.

There is an electrical switch to shut off the compressor if the system pressure goes above a set point.

What is the background of your recent AC mechanic. Someone who just works on vehicles or more institutional and commercial equipment.

Are you working from the WSM or just parts on line?

Any chance the heater core is getting hot water?

Not certain but think the thermostatic switch would be to control the air blend door to control discharge temp for those times when you do not want full cooling. It does not control the compressor.

Dave

 

[dvcochran]

My comments flow from my review of the WSM and assume the WSM covers your M9000. I have not studied the parts on line info.

More history would help.

What exactly was changed, who did the evacuation and how was the recharging done?

There are two different styles of compressor, Swash plate and scroll. The scroll has a higher output in terms of cooling. If you changed compressors, knowing which style you now have is useful.

Your system is unlike modern cars and pickups in that it has an expansion valve to control the temperature of the evaporator compared to a fixed orifice. The temp bulb of the expansion valve needs to be in contact with the evaporator outlet pipe. It is trying to keep the evaporator above freezing temperature.

There is an electrical switch to shut off the compressor if the system pressure goes above a set point.

What is the background of your recent AC mechanic. Someone who just works on vehicles or more institutional and commercial equipment.

Are you working from the WSM or just parts on line?

Any chance the heater core is getting hot water?

Not certain but think the thermostatic switch would be to control the air blend door to control discharge temp for those times when you do not want full cooling. It does not control the compressor.

Dave

The compressor, condenser, dryer, evaporator and expansion valve were changed. It is a 10PO8E compressor. I do not know if it is a scroll or swash plate but it is specific to this tractor. The exp. valve bulb is direct contact with the evaporator discharge line and insulated. A vacuum was pulled overnight and held at about -33. All the parts were lightly oiled and the compressor came with 2 ounces installed. I forget the exact amount but it was charged to the factory spec and then 4 additional ounces were added for a complete open system.
I have a shutoff in the heater line. The temperature adjust is a cable that controls a valve in the hot water line.
The work was performed by myself and an experienced mechanic that I have used for 20 plus years. Neither of us can tell from the WSM what exactly the thermostatic switch does (no schematics), hence my questions.
Our local Kubota dealer trades in mostly mowers and B series tractors and cannot answer the question either.
Do you know how the thermostatic switch functions?

 

[dvcochran]

You could try jumping the pressure switch to keep it running, and then check the switch with an ohmmeter to see if it is cycling. Do the same with the thermostatic switch. Monitor pressures while doing this though in case there is something else going on.

The bigger problem with this kind of troubleshooting is that the switch in under the roof inside the blower housing which is 1-2 hour job to get to. I am hoping to understand what it does before I crack everything open.

 

[Dave_eng]

These three pages from the WSM provide pressure info related to proper switch operation. Note that on the third page, there are two switches shown in the schematic but in reality, there is one dual switch providing two functions. The schematic showing two switches is just to show both functions.

Usually, these switches are screwed into a fitting which has a schraeder valve (Tire valve stem) inside so removing the switch does not cause loss of refrigerant.

With gauges connected to the system, you should be able to see if the compressor is turning on and off at the design pressures.

Study the three illustrations of the possible pressure switch contacts.

Note that in the top and bottom possible switch positions the electrical contacts are D meaning open.

In the middle or normal operation position the contacts are E or closed so the compressor can run.

In position A the system has had a leak and there is little to no refrigerant remaining. Pressure is less than 28.4 psi and the contacts are open stopping the compressor. Electrical position D

In position B, everything normal, the contacts are closed and the compressor is running between 28.4 psi and 455 psi. Electrical position E

In position C the system pressure has gone too high, (over filling or air in the system) and the pressure is over 455 psi and the the compressor is stopped. Electrical position D

Diagnosing the switch does not require accessing the switch. Watch the pressures and the operation of the compressor clutch.

Dave

 

[dvcochran]

These three pages from the WSM provide pressure info related to proper switch operation. Note that on the third page, there are two switches shown in the schematic but in reality, there is one dual switch providing two functions. The schematic showing two switches is just to show both functions.

Usually, these switches are screwed into a fitting which has a schraeder valve (Tire valve stem) inside so removing the switch does not cause loss of refrigerant.

With gauges connected to the system, you should be able to see if the compressor is turning on and off at the design pressures.

Study the three illustrations of the possible pressure switch contacts.

Note that in the top and bottom possible switch positions the electrical contacts are D meaning open.

In the middle or normal operation position the contacts are E or closed so the compressor can run.

In position A the system has had a leak and there is little to no refrigerant remaining. Pressure is less than 28.4 psi and the contacts are open stopping the compressor. Electrical position D

In position B, everything normal, the contacts are closed and the compressor is running between 28.4 psi and 455 psi. Electrical position E

In position C the system pressure has gone too high, (over filling or air in the system) and the pressure is over 455 psi and the the compressor is stopped. Electrical position D

Diagnosing the switch does not require accessing the switch. Watch the pressures and the operation of the compressor clutch.

Dave

Thanks, this switch we found in the WSM. What about the thermostatic switch? It sets just behind the blower housing and the bulb slides inside the fins of the evaporator. Do you see it on your WSM? I cannot find it.

 

[Bulldog]

Have you washed the radiator really good? From my experience with my 9000 they can look clean but still be full of weed seed and such. When mine has been dirty the compressor will cycle fast and not cool good. During hay season I have to wash mine out daily or it doesn't work properly.

The fan makes it really hard to clean the radiator very well and a lot of times that's where the problem has been on mine. A radiator genie has been a life saver for me.

 

[Tughill Tom]

Need to see the actual system PSI to diagnose the switch. But I'd look at what Bulldog said, sounds to me like a dirty condenser coil at this point.
wet it down and soak with Simple Green or what ever you have on hand and rinse and repeat a couple of times. Good luck!

 

[wgator]

Thanks, this switch we found in the WSM. What about the thermostatic switch? It sets just behind the blower housing and the bulb slides inside the fins of the evaporator. Do you see it on your WSM? I cannot find it.

I think it is called a thermostat in the WSM cabin section on page 10-M57.
The following is the text from it:

If the evaporator fin temperature, that is, refrigerant vaporizing temperature, drops below 0 °C (32 °F), frost or ice will form on the fins, causing a decrease in air flow and lowering cooling capacity. To prevent such frosting, and also to allow setting cabin interior to desired temperature, a thermostat has been installed.In this system, gas type thermostat is used.
The gas type thermostat has a capillary tube which is filled with special gas. The capillary tube is connected to the diaphragm chamber. The tip of the capillary tube is positioned on the evaporator fins.
When the evaporator fins temperature is higher than setting temperature of the thermostat, the micro switch in the thermostat is turned ON by increasing the pressure in the diaphragm chamber. When the evaporator fins temperature is low, such is in winter season, the microswitch is turned OFF because of the pressure in the diaphragm chamber and spring tension drops, thus turning OFF the magnetic clutch to prevent the evaporator from frosting.
(Reference)
Thermostat setting temperature
OFF .......... Approx. 1 °C (34 °F)
ON ............ Approx. 4.5 °C (40.1 °F)

The following link is to the page in a online WSM: BY CLICKING HERE

 

[dvcochran]

Have you washed the radiator really good? From my experience with my 9000 they can look clean but still be full of weed seed and such. When mine has been dirty the compressor will cycle fast and not cool good. During hay season I have to wash mine out daily or it doesn't work properly.

The fan makes it really hard to clean the radiator very well and a lot of times that's where the problem has been on mine. A radiator genie has been a life saver for me.

Last season when the condenser was off I used coil clean and cleaned the radiator really well. Later last season I did it again on both the condenser and radiator. I blow them both out once/or twice a day. More if needed on a really dry, dusty day.
Do you use water regularly on yours?

 

[dvcochran]

Have you washed the radiator really good? From my experience with my 9000 they can look clean but still be full of weed seed and such. When mine has been dirty the compressor will cycle fast and not cool good. During hay season I have to wash mine out daily or it doesn't work properly.

The fan makes it really hard to clean the radiator very well and a lot of times that's where the problem has been on mine. A radiator genie has been a life saver for me.

When the condenser was off I used coil clean and washed the radiator really good. I did it again late last season on both the radiator and new condenser. I blow out once or twice a day, more if baling on a dry, dusty day.
Do you use water regularly?

 

[dvcochran]

I think it is called a thermostat in the WSM cabin section on page 10-M57.
The following is the text from it:

If the evaporator fin temperature, that is, refrigerant vaporizing temperature, drops below 0 °C (32 °F), frost or ice will form on the fins, causing a decrease in air flow and lowering cooling capacity. To prevent such frosting, and also to allow setting cabin interior to desired temperature, a thermostat has been installed.In this system, gas type thermostat is used.
The gas type thermostat has a capillary tube which is filled with special gas. The capillary tube is connected to the diaphragm chamber. The tip of the capillary tube is positioned on the evaporator fins.
When the evaporator fins temperature is higher than setting temperature of the thermostat, the micro switch in the thermostat is turned ON by increasing the pressure in the diaphragm chamber. When the evaporator fins temperature is low, such is in winter season, the microswitch is turned OFF because of the pressure in the diaphragm chamber and spring tension drops, thus turning OFF the magnetic clutch to prevent the evaporator from frosting.
(Reference)
Thermostat setting temperature
OFF .......... Approx. 1 °C (34 °F)
ON ............ Approx. 4.5 °C (40.1 °F)

The following link is to the page in a online WSM: BY CLICKING HERE

Thank you. I have a paper copy of the manual and could not find this. I have perused Manuals Lib but not well enough apparently.
I read this to say when the thermostatic switch sees 32°F it drops out the compressor. Do you agree? Do you know if the bulb should be insulated? Do you think if I move the bulb closer to the front of the front of the evaporator (i.e. less conditioned air going across it) it may take longer to be satisfied?

 

[wgator]

Thank you. I have a paper copy of the manual and could not find this. I have perused Manuals Lib but not well enough apparently.
I read this to say when the thermostatic switch sees 32°F it drops out the compressor. Do you agree? Do you know if the bulb should be insulated? Do you think if I move the bulb closer to the front of the front of the evaporator (i.e. less conditioned air going across it) it may take longer to be satisfied?

Question 1: If working properly, when it senses 34 deg. it will shut off the compressor to keep the evaporator from freezing.
Question 2: No the sensor bulb should not be insulated.
Question 3: If the sensor bulb is installed in the original position you should not move it.
I took college courses and worked HVAC for a couple of years, the main reason the evaporator would freeze is low refrigerant charge, another reason is restricted filters.
If I read your original post right you said it is cycling on and off fast now. If the system has the proper charge and the filters are clean, low ambient air temperature will also cause this.

 

[flipmeister1950]

If you have the older roof mounted AC unit, remove the plastic shroud (under the roof) and clean both the evaporator and the heater core with compressed air. If newer, under the seat, remove the seat and shroud and clean them. The evap and heater cores get loaded with dust and need cleaned out every few years

Sent from my C6743 using Tapatalk

 

[flipmeister1950]

Last season when the condenser was off I used coil clean and cleaned the radiator really well. Later last season I did it again on both the condenser and radiator. I blow them both out once/or twice a day. More if needed on a really dry, dusty day.

Do you use water regularly on yours?

Between the AC condenser and the transmission cooler and the radiator itself, the rad fan has to work pretty hard pulling enough air through all those radiators to exchange heat efficiently, so I added a 12 volt automotive cooling fan in front of the AC to better move the air. I wired the fan via a relay to the compressor feed so when the magnetic clutch engages, the fan comes on

Sent from my C6743 using Tapatalk

 

[Bulldog]

When the condenser was off I used coil clean and washed the radiator really good. I did it again late last season on both the radiator and new condenser. I blow out once or twice a day, more if baling on a dry, dusty day.
Do you use water regularly?

Up until last year I always used water. Air didn't get it clean enough by itself. Last year I mounted a electric fan in the front (blows front to back) that turns on when the a/c clutch kicks in and I don't want to get it wet any more than I have to. Now I wash the radiator from back to front and use air for the a/c.

By the way the electric fan made a big difference.

 

[lugbolt]

in addition, its possible that the thermostatic switch could have been the problem all along....I don't know this but I'll explain.

When (if) the evap freezes over, airflow drops, and refrigerant is in liquid state. With no warm air flowing over the evap, there is a chance the liquid refrigerant could get back to the compressor which will destroy the compressor.

yes I have had to replace one or two of those thermostatic switches. Been several years since I seen the last one.

 

[dvcochran]

Up until last year I always used water. Air didn't get it clean enough by itself. Last year I mounted a electric fan in the front (blows front to back) that turns on when the a/c clutch kicks in and I don't want to get it wet any more than I have to. Now I wash the radiator from back to front and use air for the a/c.

By the way the electric fan made a big difference.

I have done the same and so far have been mounting it with heavy plastic ties with no problems. When I need to use water (3-4 times/year) I cut the ties and move the fan out of the way. Has worked well so far.

 

[SidecarFlip]

Kubota's seem notorious for not enough rad fan induced air flow across the various heat exchangers. Had that same issue with my 5030 HSTC years ago and had to add an auxiliary fan, just like I added to my M9000. On he 5030, I also had to add rubber air flow directors in front of the heat exchangers to get the air flow more directed.

It's a marginal system across all the models it seems like. I'd prefer a reverse direction air flow like JD uses on their tractots.

I'm on the process of cleaning put my roof heat exchangers right now and it's a job, but a necessary one.

I would also strongly recommend lining the underside of the roof with foil-bubble-foil Reflectix to reduce the radiated heat from the roof as it absorbs the sun's heat. You need to do everything possible to improve the marginal efficiency. My outlet temps run anywhere from 40 degrees (fan on high om ac mode) at 2000 rpm to 55 degrees at an idle. You have a lot of square inches of glass and a lot of greenhouse effect to overcome. The climate control systems need all the help they can get.

This time, when I removed the roof, I noticed it was cracking through the insert mounting holes so I had to strip out all the inserts and fiberglass each of the insert holes and replace all the inserts. Problem is, Kubota uses a 'huck' style insert that takes a special compression tool to set so I had to machine my own blind inserts. Wasn't about to buy a new roof to the tune of 1500 bucks and then have to buy the gasket separately.

I clean mine every few years as a routine maintenance thing.