Ultra Cab II AC issues, problems

[plainsman]

I have an M6800 with the Ultra Cab II. I have had issues with the air conditioning system for years. I have had a few mechanics look at the problem but none have found the solution.

When you first turn the AC on it blows as cold as you could ever ask. But, after a few minutes, it's just as if you shut the compressor off and it blows warm air. I know there are components in the roof of the cab for the AC system and that may be where the problem lies.

I have not had the tractor to a Kubota dealer yet. Main expense is transportation. Closest dealer is 50 miles and transportation at $100/hr, it will cost me $400 just to get to and from the dealer. I certainly don't mind paying a fair price for parts and labor to fix the problem.

Any light that anyone can shed on the possible cause of this problem will be greatly appreciated. I'm about ready to give up and spend what it takes to get to the dealer.

 

[lugbolt]

Very common complaint with that line of tractors in these parts as well, and similar climates as yours.

Could be a number of things ranging from a dirty evaporator core, slipping belt, compressor failing, or expansion valve failing. All are fairly easy to test with the right test equipment, which is expensive.

Now the important question. Has anyone added refrigerant in the past? If so, what kind? Leak seal? Leak seal can kill an A/C system. A tech should know the history if he is to work on it, otherwise it's entirely possible that they may have to do a complete rebuild and flush of the system in order to get back to factory specifications, which is obviously going to be a little expensive.

I can't say I've experienced a multitude of the same problem with the 6800's, 9000's etc, I've had to replace expansion valves, switches, compressor clutches, compressors, evaporators, hoses, lines, belts, idlers, about every single component on many different tractors and I can't remember any single failure prone part. 6 of one and a half dozen of the other.

I can say this: Those tractors-when the a/c is working like it should-will FREEZE you out of the cab. They work great!

 

[plainsman]

I've recently had the belts replaced (both drive and AC), evaporator core cleaned, freon checked, and compressor checked, by supposedly one of the best auto AC men in my area. I think it's time to do what I have to to get it to a dealer service shop. You're right about freezing you out - when it blows cold, you're cold.

 

[William1]

Most common cause of a refrigeration system working then stopping until it has been turned off for a while is freeze up. It could be as simple as a drain that is clogged or a temp sensor failing to shut the compressor off if the evaporator gets to freezing temp.
If you can open the panel that will let you see the evaporator, run the A/C, when it stops blowing cold, look at it, if it is iced up, yopu know it is freezing yp, if it is filled with water, you know it is a clogged drain (though it is easy to check, just blow some compressed air in the drain line, if it flows, it is clear). A mouse nest too, can be there, get saturated with water and freeze up.

 

[plainsman]

William, when you say "open the panel that will let you see the evaporator", do you mean the roof cover? I see a drain line on one side running down from the top that does drip condensate when the AC is working. I see another one on the other side that never drips.

 

[William1]

William, when you say "open the panel that will let you see the evaporator", do you mean the roof cover? I see a drain line on one side running down from the top that does drip condensate when the AC is working. I see another one on the other side that never drips.

Correct. When the AC is running, there should be dripping out of the drain line (think of an ice cold drink and all the water that collects on the outside).
When you park your car one a hot day and return to it, you will see a puddle of water under it as the A/C slowly drains. Condensate will not flow but drip. It will start to drip a few minutes after start up of the A/C and often will continue for a few minutes after the A/C is turned off.
Often, one of two things happen. The drain is clogged, it fills with water and and air cannot pass over the fins (blocked by asll the water). Or, it freezes up and again, no air can pass through until it defrosts. Even a partial clog can cause issues.
If it is draining, air is passing over and it should be blowing cold air. if it stops draining, that is an indicator of the issues. Hence, if you can open the panel to the unit and monitor it and see what happens when cold air stops flowing, you can trace down the issue.
If it freezes up, that is a sensor issue (often there is a temperature bulb (little brass like line) the controls refrigerant flow to the coils that switches off the flow when it is close to freezing to prevent freeze up. So if you see frost, that is the problem.

BTW, I am no A/C expert by any means, just familiar with the principals.

 

[Jim L.]

From the description of the symptoms, it is possible that the metering device is getting stopped. Moisture or air (some non condensible) may have gotten into the system. Machine runs good until the moisture freezes and plugs the metering device.

This can happen if refrigerant was added without doing it properly.

Or if the system was opened and then not triple vac'd.

There should be someone close who is proficient with automotive air conditioning - that would be an option.

 

[BAP]

Check that the heater valve shuts off all the way. If it lets any hot coolant into the heater core it will cause the AC to shut down. We had a several tractors that we ended up putting shut off valve in the line off the engine to keep coolant from running through when the valve in the cab started to wear and leak. We would shut it off during the summer to keep AC going.

 

[lugbolt]

You can't just pull the cab top and watch the evaporator. The evap is encased in a big plastic box. The box acts as a duct of sorts. If you pull the box apart to watch the evap, it's going to freeze because of the lack of airflow. Air is blown across the evap which warms it during the heat exchange process, and that's what keeps it from freezing up-or that's what it's supposed to do, anyway.

IIRC it does have a temp probe to keep it from freezing. Could be an issue but the WSM, again IIRC, shows how to test it and the TXV operation.

Could be a million things, as mentioned already but it'll need someone proficient with a/c systems and has the tooling to properly diagnose and repair it. With that said, there are some real shade-tree's out there who can rebuild a 350 chevy and they seem to know it all. But tractor A/C systems are a little different than putting a set of rod bearings and valve cover gaskets in a SBC! This is why I mentioned tooling and expertise. There are guys who know a/c systems a lot better than I do, and those are the guys who you want working on your tractor-if you want it to work properly-and stay functional for any length of time.

 

[100 td]

X2 on possible freeze up. This can be caused by a few different things as noted previously.
I don't know this tractor, but a lot have the evaporator under the seat or besides the seat/wheel/guard in the cab and blow air from there up ducts to the roof.
This allows them to pick up a lot of dust/dirt from the floor which turns into mud on the evap fins and also can clog the drain. If your tractor is a model with the evaporator in this location, I would remove the seat and/or side panels to get access to the evaporator and get a garden hose in there and carefully wash out the evaporator and the drain hose (Ensure drain hose is clear first). Also check to see if there are filters in the fresh or return air ducts. Clean or replace them while you are there. Also look to see if there is a thermistor or capillary line from a thermostat mounted to the evaporator, ensure it is in the correct location and not floting around loose. (Do you have a WSM?) You should also be able to blow compressed air back out the ducts to ensure free flow of air in all directions and see if there are any mouse nests restricting air flow.
If there are no filters, you can add a piece of filter wool from an A/C store to the inlet of the evaporator, however, while it will reduce the amount of dust entering the evaporator, it will also generally reduce airflow quicker as it collects dirt, so you need to be aware that you need to go in and clean the wool out frequently.
Once the evap and drain is clean, you can continue down the path of diagnosis if your problems persist.
One other thing to note, if it has been gassed previously, why was it gassed, where was the leak, was the leak fixed. Airconditioners don't consume gas, but they may leak gas, and if they have, the leak needs to be found and fixed. One symptom of reduced gas is lower pressure and refrigerant volume in the evaporator which means evaporation at lower temperatures and more chance of freezing from the start of the evap circuit and starvation of liquid at the end of the evap circuit, so thermal inefficiency with possible freezing of the evap. As noted previously if moisture is in the system, then freezing/plugging of the orifice or metering device can occur which causes cold/hot symptoms.
Good luck!

 

[plainsman]

100 td, you ask if I have a WSM. I'm not sure what that is. Two different mechanics have messed with the freon in one way or another. I'm far from a mechanic so I'm not sure what they did. I'm going to hunt up that evaporator and see what I can see.

I really appreciate everyone's time and input in trying to help solve this problem. This tractor runs great but with hot and humid Southern summers, it's near impossible to work in the cab for any length of time without AC.

 

[100 td]

WSM - Workshop Manual, I would expect it to have pics of the evap etc. If you go to kubota's parts site there will be some exploded diagrams to help.
http://www.kubota.com/part/partsList.aspx

 

[100 td]

Regards the freon, possible there is moisture in the system, but not definite, could also be low on refrigerant and the low pressure cutout switch drops the compressor off. Many possibilities unfortunately.
Unless the evap is full of mud and/or drain blocked or thermister/thermostat out of place I expect you'll be up for a full degas, pressure test/leak test, replace receiver/drier, (possibly drain and change compressor oil),evacuate and regas, depends on the state of things and who is doing the job.

My 20 year old Ford(car) aircon still works well, has never been touched, I have washed out the evap a few times as it has been on dirt roads a lot of it's life.

 

[100 td]

I just had a look at the parts page, don't know your exact model, appears some are in the cab floor, some in the roof, so access may be a hassle. Roof mount 4 drains, cab mount 2 drains it appears?

 

[BAP]

Start with the simple things. Make sure the tractor's radiator and condenser are clean including the space between them. Open up the housing for the evaporator and clean it and the drains out well. I have used a garden hose to wash them out before. Both the condenser and evaporator can get very dirty and restrict good air flow causing the AC to shut down.

 

[tempforce]

if your area has high humid conditions and your evaporator is freezing up. use recirculated air instead of fresh air setting on your a/c controls. having less moisture in the recirculated air will reduce the conditions for the a/c to ice up...