M6-101 Air Conditioner can start cool but warms up under a load

[andyman]

I have a 2016 M6-101 with 300 hrs. I purchased this unit new. The air conditioner will cool with little to no load on the engine. After some time, 30 min - 1 hr, of working the tractor, such as baling hay, the air doesn't cool. It's not blowing hot air, it's just not blowing the cold air it started with and it results in the operator sweating in the cab. The air will sometimes cool again once I finish the harder work and reduce rpm's, but this isn't a guarantee. The air does seem to cool again once the tractor has sit for a time. Here are the symptoms I've noticed and actions I've taken:

1. Compressor belt is tight
2. Compressor kicks in and out constantly. When it's engaged, the air will cool. Makes me think it's something electrical but don't know where to begin.
3. Have had an AC tech check pressures and add 1 can of freon. Pressures were between 30-40 on low side when compressor engage and 250-300 on high side. I believe those numbers are correct, I can't recall with 100% certainty and don't have my notes with me currently.
4. Have cleaned all filters, inside and outside cab. Have also blown out all cooling devices such as radiator and condenser.
5. sight glass shows no air bubbles in system (goes to support point #3)

Does anyone have any suggestions that I could try? I've got hay down and the dealer can't get to it for several days. I may just have to sweat it out. Any help would be appreciated

 

[rbargeron]

The stator (clutch coil) in the compressor clutch may be failing. The stator is a coil of fine copper wire. Typical mode of failure is gradual corrosion or cracking of the internal connections, failing open as they heat up. I've had a couple Denso stators fail like this. Eventually they stop working at all.

It may work ok on startup, but as the engine (and compressor) heat up, the stator coil can become an open circuit. Test by taking the plug off the stator and checking resistance across the terminals. It should be around 4.5 ohms (cold).

AC cycling on and off is often due to low refrigerant level - but a bad stator can cause it too. If its borderline the heat of being energized can make it fail, working ok again when it cools a bit.

Attached drawing is a typical Denso compressor. The stator pulls the hub and rotor into contact.

Dealers typically replace the whole compressor. Hope you rig is still under warranty. Compressor replacement can chew up a thousand-dollar bill - a new Denso stator can be had for $65. (one model fits several compressors) In a car the labor charge can be high - should be better access on a tractor.

 

[Tx Jim]

300 psi is fairly high pressure. Check to be sure no coolant is flowing through heater hoses. I've installed manual heater hose cut off valves on my tractors just to be positive no coolant flows through heater hoses in summer time.

 

[rbargeron]

.......Does anyone have any suggestions that I could try? I've got hay down and the dealer can't get to it for several days. I may just have to sweat it out.......

Tx Jim's idea is good place to look - try clamping off a heater hose to see if it helps. If not, try jamming some thin wooden wedges into the front clearance of the AC clutch to make it run all the time. Might get cold in the cab but you can always open a door. You'll know when the wedges are slipping when you smell wood smoke.

 

[tempforce]

check fresh air vent filter, air recirc filter. check condenser for air flow. many tractors have a problem with a buildup of dust and fine particles that will prevent the condenser from cooling the freon properly..
some people when not finding other issues have added reflective insulation between the engine/transmission and the cab to reduce heat transfer into the cab... also tinting the glass will help reduce heat gain...

 

[Brick Axelrod]

You really need to know what type of refrigerant is in the system and reference a chart to gather the correct high and low side pressures, Im assuming its 134a. That said if the compressor is turning on and off it could be a bad clutch but I would say its due to a high or low pressure switch tripping the clutch out. Put a meter on the clutch plug and if its loosing voltage its a switch cutting it off. If its a high or low pressure switch look at the pressures and see what one is causing it to cut out. Those cans you buy at the parts store cause more problems than they fix for the most part, you may have overcharged it. Make sure all filters are clean, condenser is clean before doing anything.

http://acprocold.com/wp-content/uploads/2011/11/Temp-pressure-chart-33776F1.jpg

Looking at the chart and the pressures you are saying you had it sounds like you may have a restriction in the system, possibly the drier / expansion valve.

 

[Fedup]

If the compressor clutch is cycling too frequently, I guess a defective clutch coil may be a possibility, but in my experience when they fail, they fail. They don't come and go. More likely the cause would be either a defective thermostat just not sending the clutch a proper signal long enough, or a film of dust/lint over the evaporator core blocking airflow. That causes the thermostat to falsely stop signal to the compressor since the core temperature doesn't transfer to you in the cab.
If it's cycling off too soon, I'd suggest you pull the lid off the cab and check the evaporator to make sure it's clean. Much more common problem than a defective clutch.

 

[rbargeron]

...... in my experience when they fail, they fail. They don't come and go........

I always thought that too. Then my Honda would cool beautifully when first started, only to stop cooling after a 10-15 min period. It repeated like this several times. I finally checked the stator resistance - it was 4.5 ohms when cold but was open circuit after warming up. Recently my newer car was doing the same thing. The owners forums report stator problems.

 

[boz1989]

A different angle, check for a shutoff on the engine for the heater. I had the same problem, different brand tractor. The heater was off in the cab, but enough water would leak past the valve to make it miserable. I traced the hoses to the engine and shut it off there, this may not be an option on a Kubota, but I would look.

Sent from my LGMP260 using Tapatalk

 

[rbargeron]

A different angle, check for a shutoff on the engine for the heater. I had the same problem, different brand tractor. The heater was off in the cab, but enough water would leak past the valve to make it miserable. I traced the hoses to the engine and shut it off there, this may not be an option on a Kubota, but I would look....

Check posts 3 and 4 above.

 

[ACman]

To much freon causing high pressure when throttled up and high pressure switch cutting compressor off and on.

 

[lugbolt]

To much freon causing high pressure when throttled up and high pressure switch cutting compressor off and on.

Yup.
"Tech put in 1 can of freon"....meaning the tech in question had no idea what to do, so he threw a can in it thinking it was "low"-but didn't think to check for a leak somewhere. Now, did said tech purge the charge line(s) when he added said refrigerant? If not, now you've got air in the system, which air carries moisture and other compounds, which is death to a/c systems.

Was the condenser cleaned? Not just the screen...the actual condenser? Radiator clean? Intercooler clean? The fan is behind all of that stuff, and if anything between the fan and the condenser aren't free-flowing, you'll have a lack of air flow, which results in high high side pressure and lack of a/c performance. 300 psi on high side is high. 40psi on the low side is on the higher end of what I like to see. The system WILL cycle the compressor, this is perfectly normal. There's a switch that turns it on and off as needed.

Finally, a 30 degree drop from ambient is considered pretty good. So if the air outside is 100 degrees, and your vent temps are 70, I wouldn't change a thing. But to some, if it can't get into the 40's inside the cab, it ain't cool enough. I ask this question to folks who call me every year this time of year and they get mad when I tell 'em that 30 degrees is very acceptable--and normally they are the same people that keep their house at 62 degrees in the summer.

Oh, and BTW, tinted windows help a BUNCH.

 

[andyman]

Thanks everyone. I had another ac tech check it out and it was overcharged.

 

[Tx Jim]

Thanks for update. I'm glad you got AC cooling. I'm curious is your tractors sight glass clear or have bubbles in it when AC is cooling???

 

[Churcael]

Thanks for the advice, now my aircon works fine. I've had precisely the same problem - the aircon stopped to blow air after 20 minutes of working. It was something unreal to work under the summer sun without cold air. I would even say - it was impossible to work more than 1 hour. For my house air conditioner, I'm using this chemical cleaning service https://www.airconservicing.org/type-of-aircon-service/, but I didn't know how to fix my tractor aircon. I get that something is not right after my compressor kicked in and out constantly (before the aircon stopping). Hopefully everything will be okay.