M108S AC Heat Sensitizing Tube

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
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.
Dusty, thanks for the reply, not much help, but thanks just the same.
 

Fordtech86

Well-known member
Lifetime Member

Equipment
L3200
Aug 7, 2018
3,268
2,279
113
Pineville,LA
I would think that would be tied to the temperature switch?
Im not sure how it’s set up on the tractor so I can’t help there (has to be tied to the temp control somehow, not sure if it’s electrical or cable operated). Just trying to throw out some other things to check.
 

Flintknapper

Well-known member

Equipment
L2350DT
May 3, 2022
346
408
63
Deep East Texas
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. View attachment 84800
Your TXV is a block type (possibly Denso) and is not controlled in any way by an outside source. The hat section on top is filled with the same refrigerant the system uses (and thus reacts thermally the same). By expanding or contracting it opens or closes the needle valve letting more (or less) refrigerant into the evaporator as needed.

It should have a screen type filter built in. IF you did not replace the drier when you did the A/C work then the desiccant bag may have ruptured. When that happens the refrigerant carries it to the TXV where it collects. Looks like very fine sand or dust. Just something to check if you have to go back into the system.

Most A/C systems utilize a 'thermistor' or Capillary tube to prevent your Evaporator from freezing up. IF you didn't see anything attached to the evaporator itself then you don't have a thermistor. Instead...probably a capillarity tube mounted elsewhere.

It IS important to pull a deep vacuum on the system prior to recharging (as it sounds like you did). You did not state how much vacuum you were able to achieve. Depending on elevation....I would want to see at least 28-29Hg. It takes time for any moisture in the system to boil off and be removed.

Then make sure you turn off all valves BEFORE you shut of the vacuum pump. IF you used a rented or borrowed pump...you should fill it with NEW oil before pumping down the system.

Your high and low pressures are not necessarily out of line....depending on the ambient temperature when you took the readings. Also 'under hood' temp will contribute to the readings.

Do you have a small vent type thermometer you can check vent temps with?

38 degrees.jpg


Some good suggestions have been made above. Definitely check to see if your blend door is fully closing, and IF your system (for the heater core) has a shut off valve in one of the hoses, turn it off in the summer. Many folks opt to add one if your system doesn't already provide for such.

I like to see refrigerant 'weighed in' when starting with an evacuated system, that way we know you have the correct amount installed...but I understand that most folks don't have a scale to do so (even postal scale would work).

When charging the unit be sure to 'purge' the service line of air before opening any valves on your manifold set or you'll be introducing air into the system.

With respect to lubricating oil, sounds like you've replaced the critical components and along with that removed the oil previously in there, so adding the prescribed amount of PAG oil (and proper viscosity) was the correct thing to do. TOO much oil will result is reduced cooling capability and raise system pressure. Too little will cause premature wear of your compressor.

Be sure you have adequate air flow across/through your Condenser. IF you don't all else is an exercise in futility.

As you've discovered....when doing A/C work, it is imperative that it be done right and that every part of the "System' is working correctly. Because its usually expensive and a royal pain in the butt to do, we don't want to be doing it twice (or more).
 

TxCuzzz

New member

Equipment
M108S M5640 B7510
Aug 4, 2022
12
1
3
77901
Im not sure how it’s set up on the tractor so I can’t help there (has to be tied to the temp control somehow, not sure if it’s electrical or cable operated). Just trying to throw out some other things to check.
Fordtech86,

Looking at the diagram of parts in the area of the piping for cold and hot fluids up at the evaporator and heater cores, they list servo motors. I am going to speculate that it is electrical and not cable operated.

You make a very good point that if a valve is not closing (or opening) properly then i might not be getting straight AC cold air, but a combination which results in warmer air.

This is something else i will check when i work on it next week, if i can find wom
Your TXV is a block type (possibly Denso) and is not controlled in any way by an outside source. The hat section on top is filled with the same refrigerant the system uses (and thus reacts thermally the same). By expanding or contracting it opens or closes the needle valve letting more (or less) refrigerant into the evaporator as needed.

Great info on how it works! I bought the exact part number called for in the parts diagram, so i have to assume it comes filled with the R134a. Do not remember anything in the description about that.

It should have a screen type filter built in. IF you did not replace the drier when you did the A/C work then the desiccant bag may have ruptured. When that happens the refrigerant carries it to the TXV where it collects. Looks like very fine sand or dust. Just something to check if you have to go back into the system.

I have actually replaced both the expansion valve and the drier twice. I do not remember the sand or dust, but will look carefully at it when i work on it next week. Since i am going to have to take the roof pan off again, i might just opt to replace them both a third time, to be on the safe side, They are not that expensive.

Most A/C systems utilize a 'thermistor' or Capillary tube to prevent your Evaporator from freezing up. IF you didn't see anything attached to the evaporator itself then you don't have a thermistor. Instead...probably a capillarity tube mounted elsewhere.

It IS important to pull a deep vacuum on the system prior to recharging (as it sounds like you did). You did not state how much vacuum you were able to achieve. Depending on elevation....I would want to see at least 28-29Hg. It takes time for any moisture in the system to boil off and be removed.

I can tell you that for sure it was under 0, and the gauge only goes to -30. I will be sure and make a note of it in the future. I vacuumed the system for hours as i was told the longer the better.

Then make sure you turn off all valves BEFORE you shut of the vacuum pump. IF you used a rented or borrowed pump...you should fill it with NEW oil before pumping down the system.

I am pretty sure i closed the valves before turning it off, but will make it a point to do so in the future. I bought the vacuum pump new for this job so it is new oil in it.

Your high and low pressures are not necessarily out of line....depending on the ambient temperature when you took the readings. Also 'under hood' temp will contribute to the readings.

Do you have a small vent type thermometer you can check vent temps with?

I have a meat thermometer and also an IR heat gun to check the temps with.

View attachment 84845

Some good suggestions have been made above. Definitely check to see if your blend door is fully closing, and IF your system (for the heater core) has a shut off valve in one of the hoses, turn it off in the summer. Many folks opt to add one if your system doesn't already provide for such.

I will check and see. If it does i will turn it off and if not, will check and see if someone offers a kit to install one.

I like to see refrigerant 'weighed in' when starting with an evacuated system, that way we know you have the correct amount installed...but I understand that most folks don't have a scale to do so (even postal scale would work).

My next purchase was going to be a scale, and will look into a postal scale as well,

When charging the unit be sure to 'purge' the service line of air before opening any valves on your manifold set or you'll be introducing air into the system.

I was aware of this and did so to remove all of the air in the line.

With respect to lubricating oil, sounds like you've replaced the critical components and along with that removed the oil previously in there, so adding the prescribed amount of PAG oil (and proper viscosity) was the correct thing to do. TOO much oil will result is reduced cooling capability and raise system pressure. Too little will cause premature wear of your compressor.

Yes, i flushed the lines, installed all new components, then after purging the system, and while there was still a vacuum on it, used the syringe tool for measuring out compressor oil and connected it directly to the LO side (if i remember correctly).

Be sure you have adequate air flow across/through your Condenser. IF you don't all else is an exercise in futility.

YES! We have found that we actually have to clean it daily in order to get the AC to function anywhere near normal during the summer.

Like i stated in a previous post, early in the morning it blows cold, and causes condensation on the rear window and you have to turn the vent off of you and run on low. As the ambiant temperature rises and the radiant heat from the engine and transmission build, it blows warmer and warmer. It did not used to do this.


As you've discovered....when doing A/C work, it is imperative that it be done right and that every part of the "System' is working correctly. Because its usually expensive and a royal pain in the butt to do, we don't want to be doing it twice (or more).

So i am retired and in my mid 60's and have been many things in life. Motorcycle mechanic (we raced them) machinist, salesman, etc., etc.. I have always enjoyed working on things and either repairing them, or making them. A person can take pride in a job well done.

I like the idea of fixing things and saving money in the process. I also like learning and know that there is always a learning curve. Sometimes it is steeper than others.

All in all, when i get this done and working properly, i will still have saved money over having taken it to the dealer and saving money in todays day and age is a big benefit to working on it yourself.

Also think about this. This thread is a rather long one, quite detailed in the information flowing in both directions and i think it is going to be a big help to others in the future.

I want to thank all of you who have contributed to this point and i encourage others to chime in and offer up suggestions and thoughts.

I want to thank you for taking others ideas and comments and expanding upon them and also giving me other things to check and think about.

I am going to tame this beast with the help of my online support crew!
 
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