M9000 A/C Thermostatic Switch

[dvcochran]

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.

On the ones you changed out, had they totally failed (not working at all) or were they not working within the temperature/pressure specs?
I have been pulled away from this project and hope to get back on it this week. I have looked over the WSM and will check the chare and cycling of the two switches.
To be clear, IF the charge is correct and there are no other problems, the dual type pressure switch (10-54 in WSM) should always be in the ON (B) position? Or should it eventually go to position (C) as pressure builds in a 'normal' cycle?
The thermostatic switch, which is in series with the pressure switch, is purely a failsafe to prevent the evaporator from freezing over? With my discharge temp so high, unless it is opening very early I more suspect the pressure switch at this point.
I have to put the gauges on and pull the roof.
Any other suggestion?

 

[dvcochran]

I was finally able to pull the roof and put gauges on the system. It was a cool day yesterday, about 60°. After running the tractor for a while I idled it up to 1500rpm. The pressures with the compressor running were about 20 on low side and about 200-220 on the high side. When the compressor cycled off the low side would go up to about 30-35 and the high did not change much at all. Watching the sight glass I would see bubbles when the compressor cycled Off but none while it was running. This mostly cleared. The compressor was cycling a lot it seemed.
Are these pressure indicating a low charge for a 60° day with the tractor inside the shop?

The thermostatic switch is definitely working; whether it is 100% right I am still not sure. You can hear the switch change state and confirm it by the compressor cycling. I can jumper the switch or remove the bulb from the evaporator and the compressor will keep running. The evaporator temp would pull down close to 20° if I left the bulb out in free air. It would frost up the evaporator lines big time.
With everything in place, I had a analog thermometer in the evaporator. It is a small dial type gauge so it is hard to tell the exact temp but the switch did seem to be changing state pretty close to 34°.
It does seem as though the more I futzed and moved the bulb around the better it seemed to work.
There are two places where the fins are bent on the evaporator and it is hard to tell which is the original location. For test purposes I placed the bulb in the spot nearest the rear of the evaporator (closest to rear of tractor) a different location from where it was which close to the front.
I put my thermometer in a vent and running at 1500 rpms in the shade on a cool day the discharge temp was about 40° which I don't remember ever seeing.
So, my main questions are:
1.) Based on the pressures should I add charge now or wait for a hot day and do it with the tractor in the sun? According to the WSM high pressure cutout is at 455°.
2.) Since the thermostatic is working at something that appears close to 34° how/when do I decide it needs to be replaced? This switch is $265 from Kubota and I cannot find it anywhere else. I do not see anything else dropping the compressor out.
3.) Does it matter where the thermostatic switches bulb is located in the evaporator?

 

[SidecarFlip]

60 degrees is to cold (ambient), you need it to be about 75-80 to check and your low side pressure is a bit low as well. I want 35 on the low side with the compressor running.

 

[Jim L.]

It was a cool day yesterday, about 60°.

Not a good temperature for taking pressures. The WSM is probably 86F for factory pressures. Compensate for ambient temperature by using a temperature to pressure chart for your refrigerant. Better results with a 95F ambient.

It does seem as though the more I futzed and moved the bulb around the better it seemed to work.
There are two places where the fins are bent on the evaporator and it is hard to tell which is the original location. For test purposes I placed the bulb in the spot nearest the rear of the evaporator (closest to rear of tractor) a different location from where it was which close to the front.

By moving it around you probably got better thermal/mechanical contact.
In theory, you want to measure at the input to the evaporator where the temperature should be close to 40F. As the evaporator picks up heat, the temperatures will rise the further along the evaporator to the outlet. Evaporator design points are typically 40F to provide a margin to keep the evap from icing.

First, as already mentioned, there has to be good airflow across both evaporator and condenser. The system will not charge properly until this happens.

At a known ambient temperature, factory set point or 95F, read pressures and temperatures to accurately charge. Charging can not be done by sight glass. You need a baseline at a known operating point to zero in on any problems.

 

[jack_frost]

I have a Kubota either. I've bought it a year ago, so there wasn't any breakdowns yet. I hope there won't be any for another year. However, I've had a difficult situation with my air conditioning system in the house. Our system was old and worked really weak. I decided to change it to the new one. I'm not a technician, so I found one on the internet. He seemed adequate, so I didn't really watch after him. It was such a mistake from my side. After few days all the electricity in the house was down. When we called another guy from https://www.airconservicing.org/why-choose-us/ after my neighbor's advice, he was terrified. He did just a big job fixing the electricity and A/C system. I guess it was a lesson for my whole life to not call random workers.

 

[DustyRusty]

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?

My concern is how much oil and refrigerant you added to the system. You don't "charge" with oil, you add the oil to the crankcase of the compressor, and then you hand turn the compressor over about 10-20 times till you disperse the oil into the system. Then you will draw the vacuum, and after whatever time period that you feel comfortable with, you pressurize the system with nitrogen to check for leaks under pressure, that many times will not show under a vacuum. I usually pull the system down for at least 24 hours, and also use a micron gauge as a back up to the vacuum gauge. Once I am satisfied that the system holds a vacuum, I will pressurize it with nitrogen and hold it for another 24 hours. If it is tight, then I evacuate it again, for a minimum of 4 hours, and charge with refrigerant, using a scale to measure exactly how much I am installing. Refrigerant oil is measured in liquid ounces, and your refrigerant charge is measured by weight.
At this point, I don't believe that you are exactly certain what was done, or how it was done. If this was originally a R12 system, and you charged it with R134, then you have to reduce the weight amount of refrigerant by 20% and use only 80% of the originally called for amount. I never do a conversion on a R12 system, because systems that work well on R12, might not always work well on R134. There is a lot more to refrigeration than just replacing parts and installing a refrigerant.
To answer your other question about the bulb, it has to be installed tightly on the side of the tube, and it should be wrapped with cork to keep it isolated from the outdoor ambient temperatures. Working on mobile refrigeration is a lot different than working on stationary refrigeration. The principals are similar, but the applications are a world apart. A mobile system from the 1980's is not the same as a system from the 1990's, because how they are regulate refrigerant changed over the years.

 

[kubotafreak]

Pressures seem off to me. Did you install a new expansion valve, and drier? As others have said, the electronic thermostat should be right in the center of the evaporator and need no adjustment. The expansion valve sensing tube and diaphragm cap should be covered with adiabatic tape. The sensing coil is to be attached to the low side line to sense the temperature. The adiabatic tape covers this assembly. I believe your pressures are off. For that low of ambient you need lower high side pressures. These tractor ac systems take less than cars. The charge is very sensitive. So you really need to have the system running with a moderate engine speed to charge correctly. It is very important for both coils to be clean. I assume the previous setup had r134, so this is not a convert. I know 9000's are a little vintage. You will know if the evap is freezing up because you will have a drastic reduction in cabin flow. Shouldn't need to take anything apart to tell this. If it is a convert, you at minimum should have solvent flushed the lines, and replaced compressor, expansion, and drier. No mineral oil can remain for r134 systems.