M108S AC Heat Sensitizing Tube

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Compressor died on our M108, so we proceeded to replace all items i could find in the WSM, and by using the online parts diagrams. Charged up freon and oil per the WSM, but could never get the pressures to come close to what the WSM says they should be. It got cold in the morning, but as the sun rose it could not keep up. It had been a beast when it came to AC.

Today while reading the WSM again, i found a section i had missed talking about the Expansion Valve (which i replaced) and the Heat Sensitizing Tube???

This is the first time i had seen anything about it (i missed it) and the first time i found it hidden on the parts diagram,

My question is this, it appears that there is some sort of a blockage in the system which is not allowing the pressures to level out anywhere near what they should be. LO and HI sides are too high.

What is the purpose of the Heat Sensitizing Tube, what does it regulate, how is it properly installed and how does it interact with the other components?

WSM simply says if the heat sensitizing tube is correct, then replace the expansion valve.

Before you ask, yes i am 100% sure i replaced all other components in the system. lol

I appreciate any and all advice and if i still have missed a detailed explanation in the WSM please let me know.



050 T1065-72162 SUB-ASSY THERMOSTAT ** Replaces T1065-72160 **
M108s AC.png


Stay cool and safe.
 

Attachments

Dave_eng

Well-known member
Lifetime Member

Equipment
M7040, Nuffield 465
Oct 6, 2012
4,680
662
113
Williamstown Ontario Canada
Do not know your system.
In my world this heat sensing tube is a capillary tube placed between the fins of the evaporator to sense what is happening in the evaporator and then controlling the expansion valve. I believe the top of your expansion valve has a metal diaphragm to which is soldered the heat sensing tube.
This image is generic not your M108S
forum heat sensing tube.jpg

Could be completely wrong when it comes to your machine.............
Dave
 
Last edited:

Edke6bnl

Member

Equipment
B7800 Kubota, case 1840 Skidsteer Ford 3500
Mar 31, 2022
52
12
8
Agua Dulce, California
The expansion valve will sense a need for more cooling and it will safely flood the evaporator with refrigerant to increase cooling but also prevent flooding back to compressor. Did you evacuate the system before charging?
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
The expansion valve will sense a need for more cooling and it will safely flood the evaporator with refrigerant to increase cooling but also prevent flooding back to compressor. Did you evacuate the system before charging?
Yes on the evacuation. IN fact, i let it run for several hours. The first compressor we put on it was defective and failed immediately. So it had to come off and it was evacuated again. Then after using tractor for a little while one of the hoses blew, and it had to be replaced. Once again evacuated the system for several hours. I have been working on this for a total of 40 to 60 hours with all of the items we have had to change and then change again. The only thing i missed is the heat sensitizing tube.
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Do not know your system.
In my world this heat sensing tube is a capillary tube placed between the fins of the evaporator to sense what is happening in the evaporator and then controlling the expansion valve. I believe the top of your expansion valve has a metal diaphragm to which is soldered the heat sensing tube.
This image is generic not your M108S
View attachment 84789
Could be completely wrong when it comes to your machine.............
Dave
DAve thanks for the reply. The expansion valve for this tractor looks nothing like the TXV valve and did not have a wire attached to it. It is called a block type valve. Here is a picture of the one on my Kubota. No wire was attached to it.
M108S expansion valve.jpg
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Compressor died on our M108, so we proceeded to replace all items i could find in the WSM, and by using the online parts diagrams. Charged up freon and oil per the WSM, but could never get the pressures to come close to what the WSM says they should be. It got cold in the morning, but as the sun rose it could not keep up. It had been a beast when it came to AC.

Today while reading the WSM again, i found a section i had missed talking about the Expansion Valve (which i replaced) and the Heat Sensitizing Tube???

This is the first time i had seen anything about it (i missed it) and the first time i found it hidden on the parts diagram,

My question is this, it appears that there is some sort of a blockage in the system which is not allowing the pressures to level out anywhere near what they should be. LO and HI sides are too high.

What is the purpose of the Heat Sensitizing Tube, what does it regulate, how is it properly installed and how does it interact with the other components?

WSM simply says if the heat sensitizing tube is correct, then replace the expansion valve.

Before you ask, yes i am 100% sure i replaced all other components in the system. lol

I appreciate any and all advice and if i still have missed a detailed explanation in the WSM please let me know.



050 T1065-72162 SUB-ASSY THERMOSTAT ** Replaces T1065-72160 **
View attachment 84788

Stay cool and safe.
ALL HERE IS SOME MORE INFO.

Here is the picture of the heat sensitizing tube. The block/sensor looks to have two prongs which most likely have a female connection connected to them. There is also a probe on one end that i would imagine as Dave said it is inserted into a cooling fin? Might this be into the evaporator coil since it sits right next to where it is mounted inside the plenum (my description, may not be correct)?

When i removed and replaced the evaporator coil, i do not remember any wire/probe being attached to it. I simply slid the old one out and put the new one in and closed the plenum up. The expansion valve sits just outside of the plenum and attaches to the fittings of the evaporator coil that protrude out.

I have yet to find an exploded parts view that shows the heat sensitizing tube installed and where it goes. Also need to know where the sensor is connected to.

There is a connection on the Hi/Lo pressure switch that also resides right in that area, so perhaps it connects to a wiring harness that also connects to the sensor in question.

I appreciate all of the input and please keep it coming. I think I/we will be able to work thru this before i climb up there and remove the roof pan once again. LOL

Thanks.
T1065-72162 SUB-ASSY THERMOSTAT.jpg
 

Fedup

Member
Apr 6, 2016
124
9
18
Winchester
I can't help asking. When you have the system operating and "the pressures on both sides are too high", just what are those pressures, and what do you think they should be?

What weight of refrigerant did you put in?
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
I can't help asking. When you have the system operating and "the pressures on both sides are too high", just what are those pressures, and what do you think they should be?

What weight of refrigerant did you put in?
Hey Fedup. So the WSM says they are supposed to be LO side 22 to 28 and HI side 185 to 241. A friend told me with R134a the LO side would probably be around 34.

WSM says system takes 2.09 to 2.31 lbs of R134a.

I also filled the system with the correct amount as specified of ND-ACEITE 8<PÁG* oil>.

I am assuming that when you ask what weight of refrigerant i put in you are referring to the 2.09 to 2.31 lbs? I did not have a precise way to measure it, so it was put in using 12oz cans and getting as close as i could.

Remember, we had to do this whole procedure several times, so each time got a little better at it.

So the last time i checked it, the LO side was around 50 and the HI side was up around 300.

Now what i posted above from the WSM says if both pressures are high, it is either the Expansion Valve or the heat sensitizing tube. Since the expansion valve is new, and i just learned of the HST, then i am hoping that is the culprit, but, would really like more info from someone in the know as to how it hooks up so i can make sure it is installed correctly.

Thanks for your questions and response.

P.S. Guess you heard about the new company that was created when UPS and Fedex merged?
 

Dave_eng

Well-known member
Lifetime Member

Equipment
M7040, Nuffield 465
Oct 6, 2012
4,680
662
113
Williamstown Ontario Canada
Could you please post the part number of the heat sensing tube.
I did a text search of the WSM and no where does it do more than mention the Heat Sensing Tube.
The Kubota WSM are more of a reference book for a trained mechanic than a "how to," book.
Is the tube attached to the switch in the image you posted a metal one?

Dave
 

Fedup

Member
Apr 6, 2016
124
9
18
Winchester
Well if you're referring to the capillary tube in the above photo, that's part of the thermostat. It's purpose is to sense temperature of the evaporator coil, then stop and start the compressor clutch as needed to adjust as needed based on your dial setting in the cab. It has no effect on pressures one way or the other when the compressor is operating.

The pressure readings are subjective. Yes 50 is a bit high for a low side, but 300 isn't really too high depending on ambient temps. Remember high side pressure can be higher when the hood is up. That can reduce airflow through the condenser. Next time you're playing with it, read the pressures, then try closing the hood just to see what difference it makes.

As for charge weight, three 12 oz cans would be slightly more than the 2.31 lbs by my math (never was too good at math). When you first hook up the gauges after the unit has been off for some time and system pressures have equalized, what do they read? Personally, during summer months I like to see about 70 to 75 psi. If I see 80 or more, I start thinking it's overcharged. Others may disagree.

So when the system is operating at these pressures, how is it working? Cold air in the cab or no?
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Could you please post the part number of the heat sensing tube.
I did a text search of the WSM and no where does it do more than mention the Heat Sensing Tube.
The Kubota WSM are more of a reference book for a trained mechanic than a "how to," book.
Is the tube attached to the switch in the image you posted a metal one?

Dave
Dave the part number is 050 T1065-72162 SUB-ASSY THERMOSTAT ** Replaces T1065-72160 ** It is the number listed in the parts diagram i posted in my original post.

I have never actually seen the part, as i did not know it existed when i took the unit apart and replaced all of the parts.

Fedup gave a good explanation, which i will respond to next.

Thanks for the reply.
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Well if you're referring to the capillary tube in the above photo, that's part of the thermostat. It's purpose is to sense temperature of the evaporator coil, then stop and start the compressor clutch as needed to adjust as needed based on your dial setting in the cab. It has no effect on pressures one way or the other when the compressor is operating.

I understand what you said above, and the compressor clutch is engaged. That has not been a problem as it seems to work properly.

So if it controls the clutch, then i wonder why the WSM says if the HST is installed properly and the pressures are both high, then the expansion valve is bad?

I am not seeing the connection between the clutch being engaged and the compressor running and the expansion valve being bad, unless they are assuming that if the HST is installed properly then it is working and if the compressor is running, then the only other thing that could be bad and cause both pressures to be high is the Expansion valve?


The pressure readings are subjective. Yes 50 is a bit high for a low side, but 300 isn't really too high depending on ambient temps. Remember high side pressure can be higher when the hood is up. That can reduce airflow through the condenser. Next time you're playing with it, read the pressures, then try closing the hood just to see what difference it makes.

I will try that and see what effect it has on my pressures. I did not think about the fact that having the hood up alters the design and thus changes the airflow. Good point!

As for charge weight, three 12 oz cans would be slightly more than the 2.31 lbs by my math (never was too good at math). When you first hook up the gauges after the unit has been off for some time and system pressures have equalized, what do they read? Personally, during summer months I like to see about 70 to 75 psi. If I see 80 or more, I start thinking it's overcharged. Others may disagree.

You are pretty much correct on your math and that is the manner in which i determined how much freon i added to the system and tried to get it within the specified amount listed in the WSM. After i had two cans in it, i kept adding it slowly and kept an eye on the gauges. I stopped for short periods of time to allow the system to stabilize as well.

I do not remember what the pressures were, but i do know that they equalized, as they should after the unit had been off for awhile.


So when the system is operating at these pressures, how is it working? Cold air in the cab or no?

Good Question. I am in South Texas and our ambiant temps have been in the mid to upper 90's with very high humidity. When you start out in the morning say around 8 or 9 (i'm retired, don't do mornings) It is blowing really cold air, cant remember what the pyrometer read, but you have to run in low fan mode and turn the vent off you. Condensation forms on the rear cab window. As the day progresses, the ambiant rises and you have to turn the fan to the midpoint then on high.

The air coming out of the vents gets hotter, as the sun beats down on the rooftop and as the radiant heat from the transmission and the engine rise thru the floorboards.

One day i tried to work all day long and about 4pm, i took some heat readings and was really surprised.

The air coming out of the vent was about 91. The temp of the floor under the seat was 145, and the heat on the door rail on the sunny side was 127. It was not a very pleasant day, and the last time i did that.

You remember the story about if you put a frog in a pan of water and turn the heat on, he will never realize he is cooking until it is too late?

Bottom line is, we mow for 3 or 4 hours in the morning, then a couple of hours in the evening and it works good enough to keep you from breaking a sweat.

HOWEVER, before the original compressor died, you never really had an issue with really hot air coming out of the vents, so what happened?

Keep offering up your comments, thoughts and suggestions. I am learning a lot and these replies are really help me think this thing thru.

Thanks.
 

Tughill Tom

Well-known member

Equipment
B3200
Dec 23, 2013
670
390
63
Turin, NY
There are non-condensable's in the system ;i.e Air and moisture. It needs to be evacuated and pulled down into a deep vacuum for hours and recharged with the proper amount of 134.
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Txcuzzz
Did you flush AC system before replacing failed compressors?
Yes. When all components were replaced, i flushed the lines out. I did not flush out all of the new components as i was advised not to.

I then pulled a vacuum on the system over night, as i was told the longer i could do so the better.

Thanks for the reply.
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
There are non-condensable's in the system ;i.e Air and moisture. It needs to be evacuated and pulled down into a deep vacuum for hours and recharged with the proper amount of 134.
Tughill,

Now that i know the purpose of the HST. my next thought is perhaps the expansion valve is bad or clogged by something that was missed in the system. I was thinking more along the lines of some sort of debris as opposed to air and moisture.

I cannot get to the AC again until sometime next week at the earliest but i had also thought about evacuating the system again and pulling an overnight vacuum on it.

What are your thoughts on going ahead and changing the expansion valve at the same time, or waiting to see if the evac, vacuum and recharge do the trick?

I really hate having to take the roof pan off again if not totally necessary.

Thanks for the reply and information.
 

Tughill Tom

Well-known member

Equipment
B3200
Dec 23, 2013
670
390
63
Turin, NY
Tughill,

Now that i know the purpose of the HST. my next thought is perhaps the expansion valve is bad or clogged by something that was missed in the system. I was thinking more along the lines of some sort of debris as opposed to air and moisture.

I cannot get to the AC again until sometime next week at the earliest but i had also thought about evacuating the system again and pulling an overnight vacuum on it.

What are your thoughts on going ahead and changing the expansion valve at the same time, or waiting to see if the evac, vacuum and recharge do the trick?

I really hate having to take the roof pan off again if not totally necessary.

Thanks for the reply and information.
I'd evac. it and pressurize with 150psi of dry nitrogen. let sit pull a vac and do the nitrogen again. Pull a vac overnight and recharge. The Nitrogen with help getting everything out of the system.

One old trick I was taught was to smack the compressor with rubber mallet while under a Vacuum to get any moisture in the oil to move out.

As far as TXV goes I'd change it if is a flare nut connections if not I'd pass on it.
 

Fordtech86

Well-known member
Lifetime Member

Equipment
L3200
Aug 7, 2018
3,268
2,279
113
Pineville,LA
So the last time i checked it, the LO side was around 50 and the HI side was up around 300.
that’s really not out of line down here if it’s sitting at idle (this time of the year). Could be slightly overcharged, but it should be cooling with those pressures. Is the blend door working properly? Does that have a coolant shut off for the heater core?

I may have missed it, but it would also be helpful to have the gauges on it while out working the tractor to see what it’s doing when it starts blowing warm.
 
Last edited:

DustyRusty

Well-known member

Equipment
BX23S
Nov 8, 2015
1,969
1,188
113
North East
Personally, you can't guess at refrigerant quantities, what seems like a little might be a lot. You also didn't mention if you replace the receiver drier each time the system was opened up. This is important because it can be holding contaminants from the old system. The system should be serviced by someone that has the correct tools to do the job properly, rather than just throwing parts and money at it in an attempt to fix it. I have done a lot of mobile air conditioning work going back 60 years, and whenever I am asked to work on a system that an owner has worked on prior, I decline, because I know that something isn't right, I just don't know exactly what, and I also know that they are not going to be willing to pay me what it is going to take to find and correct their mistake(s) along with the associated costs of replacement parts. To work on any refrigerant system, the basic list of tools required is an investment in being able to do it successfully, along with experience and education. A refrigeration scale is just one of these many tools.
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
that’s really not out of line down here if it’s sitting at idle (this time of the year). Could be slightly overcharged, but it should be cooling with those pressures. Is the blend door working properly? Does that have a coolant shut off for the heater core?

I may have missed it, but it would also be helpful to have the gauges on it while out working the tractor to see what it’s doing when it starts blowing warm.
Fordtech86, i will have to research and see if it does have a coolant shut off for the heater core. Have not seen that in my research.

Will also see how to check if the blend door is working properly. I could see where that could make it run hotter than it should if it is not closing properly. I would think that would be tied to the temperature switch?

Good thoughts. Thanks.