Another Kubota AC issue

[bunchgrass]

I have a 2012 M8540 w/ about 1600hrs on it and recently the AC started to blow less cool so, being the genius I am, I hit it with some more 134a and likely overcharged the system. I'm right in the middle of haying (hay on the ground) so I had to rake with the doors wide open at 90+ degrees out. Sucks. Had to twist the Kubota dealer to come check my system as I had cleaned every screen and filter with no luck. I pulled the seat and opened up the floor to get to the evaporator which wasn't dirty at all. The mechanic had little experience with AC (thanks) but did have a set of gauges and bled off some refrigerant until the low side was in range ( btwn 20 and 30) at idle. The problem we ran into was at operating RPM (2200), the compressor started to kick off and on about every 15 seconds. Lo side would drop to below 20. Air blows colder but not the very cold air the system has blown in the past.

Soooo ..... any ideas? Mechanic said they could evac the whole system and then refill with exact amount of refrigerant and that might help. Any possibility if it being the lo pressure switch? He seemed to think the switch was "all or nothing" so not likely a problem.

 

[dvcochran]

What was the high pressures and what was it doing while the compressor was cycling? Depending on that information, for troubleshooting purposes, I would replace the dryer and have a good vacuum pulled and a recharge to spec. If it is easy to get at on your tractor, I would also change the expansion valve at the same time. They are less that $50.
The worse news is I have always heard it is a hard rule to change the condenser , dryer, and expansion valve if the compressor has to be changed on a Kubota (and most other tractors).

I agree with the low pressure switch being good or bad. On my M9 the bulb for the low temp cutout switch on the evaporator shook loose, not touching the evaporator and would allow it to freeze up. But that sounds like a completely different situation.

A few years back my compressor went out in the middle of the first cut. Like you I suffered through 3 days of 90° heat. Good times.

 

[bunchgrass]

What was the high pressures and what was it doing while the compressor was cycling? Depending on that information, for troubleshooting purposes, I would replace the dryer and have a good vacuum pulled and a recharge to spec. If it is easy to get at on your tractor, I would also change the expansion valve at the same time. They are less that $50.
The worse news is I have always heard it is a hard rule to change the condenser , dryer, and expansion valve if the compressor has to be changed on a Kubota (and most other tractors).

I agree with the low pressure switch being good or bad. On my M9 the bulb for the low temp cutout switch on the evaporator shook loose, not touching the evaporator and would allow it to freeze up. But that sounds like a completely different situation.

A few years back my compressor went out in the middle of the first cut. Like you I suffered through 3 days of 90° heat. Good times.

First -- thank you for your reply.

There were various high pressure readings depending on what the mechanic was doing. At idle, it was around 240 (I think). When it started cycling the compressor, it went as high as 420. The high and lo acted in relation to each other as the cycling occurred (lo goes up and high goes down and vice versa).

I'll need to look at the manual to see if I can find the expansion valva

 

[lugbolt]

Straight from the EPA cert test, section 608. 609 similar.

The EPA Office of Enforcement and Compliance Assurance website accepts anonymous reports of suspected or witnessed unlawful releases of refrigerant or other violation of the clean air regulations. EPA enforces the regulations by investigating reported leaks, conducting surprise inspections, and offering rewards of up to $10,000 for information about unreported violations.

In other words, don't bleed off any refrigerant. You could be turned in and the EPA actually tells those of who're licensed that they're supposed to report it. The term "bled off" is a dead giveaway. Had you said "recovered", you'd have been better off.

Anyway--

420 psi on the high side is real high. 350 is about all I've seen on those tractors (hood up, it comes down with the hood closed due to airflow). High high side pressure is oftentimes indicative of a system that is not cooling the condenser properly, OR a TXV issue. More often the former. Just because the screen is clean doesn't mean that the condenser itself is clean. Did you wash it out? How about the fan belt. Is it nice and tight? Not slipping? Anything blocking airflow at the front of the hood (seeds stuck in the grille, etc)? Is the fan shroud broken/cracked? Are all of the deflectors in place? There are some sponges that are stuck to the sides of the radiator and they need to be there, also some are on the hood, and they also need to be there. A/C performance (and cooling system performance) almost always suffers if these sponges and deflectors are missing because air flow is disrupted. Yes TXV could have an issue but in my experience with the M-40's, it's extremely rare and usually due to debris or moisture in the system, both typically results of either poor system repair practices or failed compressor.

I'd rule out a failed compressor based solely on the pressure readings you've provided us with. Most of the time a failing compressor will have low high side pressure and high low side pressure, especially with scroll compressors.

people tend to think that compressor cycling is a bad thing. It's not. Or it could be. There is a pressure switch in the system. The pressure switch cuts the compressor off when the low side pressure drops below I think 24 psi (Based on my memory). That is designed to protect the compressor AND to keep the evaporator from freezing over. So when the cabin gets nice and cool, the pressure drops on the low side and it can cut the compressor off until the pressure rises back up. This cycle repeats, and the frequency of cycling is dependent on the pressure which is related to the temperature of the evaporator. Also, the pressure switch will cut the compressor if the high side pressure gets up there, and at 420 psi you're getting close. I want to say 440 is where it cuts out, but again I don't remember for sure (and I don't think kubota specifies in the wsm)

 

[Tx Jim]

If a dealer service manager sends a technician to repair my tractors AC he better send a technician certified in AC systems that comprehends gauge pressures if he expects me to pay the bill.

Is AC compressor & engine fan belt snug? I think this AC problem is lack of correct amount of refrigerant which a competent AC technician should get close to correct amount by viewing BOTH GAUGES.

 

[Motion]

I agree with others about starting over. You decided to add refrigerant for a reason. Before replacing parts I'd recover the refrigerant and perform a good pressure check (preferably with nitrogen and trace gas) to identify any leaks, correct any leaks if found, then at least replace the filter/dryer, pull it down to 400 microns, valve it off and do a standing vacuum test, if it holds then weight in the correct amount of refrigerant per specifications, if it doesn't hold the you either have a leak or it's flashing off moisture. Good luck

 

[bunchgrass]

Thanks to all of you for your replies. Let me try to answer/comment to some of the replies.

Let me preface this whole thing with this --- this is my local Kubota dealer (50 miles away one way) and they did not want to come out for this call. It's going to cost me $220 just for the travel time but with temps going up to 105F for the next 5 days, no AC was not an option. So they sent a guy who has worked for their dealership for 6 months and has mechaniced for a couple of farms previously but has no AC experience. I hate this dealership and routinely drive 180 miles round trip to get parts, hydraulic fluid etc from another dealer and this is my first service call ever from Kubota.

1) --- regarding the belt tightness. There appears to be a tensioner. Should that idler wheel be in contact with the belt or is it only necessary when tension is insufficient? If it is too loose why would the compressor run as it is - cycling on and off?


2) --- I personally didn't bleed or recover anything. Not to mention that I had told the service manager what to expect (potentially overcharged system) before he sent someone out so they knew that removing some refrigerant was likely. I understand about dumping directly into the atmosphere but when you have no other options for assistance, you feel you can't burn the last bridge.

3 --- my concern about compressor cycling is the frequency. On/off every 15 or 20 seconds seems like a lot.

4 --- while the tech was playing with the refrigerant I looked at the service manual online and saw a few other simple tests - like blocking airflow at the condenser with a piece of cardboard to check hi pressure [I think] or testing the resistance of the lo pressure switch. He was uninterested. I'm no AC tech for sure but neither was he.

5 ---- TXV = temperature control valve? Where would that be located? Any way to test it?


I might have to call the local Case/IH shop and get their tech out although they were ambivalent about coming out too.


I'm just not enough of a high roller to get the best service like the guys farming 2000 acres of wheat do.

 

[Fordtech86]

First it was possibly overcharged, now its possibly undercharged (would explain rapid cycling). Before throwing any parts at it I would recommend a complete evac and recharge to the proper level before trying to diagnose.

Not sure of your area but a call to a local auto repair shop may get you someone too. Ive worked at dealerships that would take almost anything in.

 

[Jim L.]

I'm sorry to hear that the A/C is misbehaving.

TXV is a thermostatic expansion valve. Means that instead of just an orifice turning liquid to vapor, it has feedback to measure the right amount under different conditions.

Pressures need to be taken with their corresponding ambient temperature and sometimes humidity.

What I would suggest is an experienced automotive A/C person who knows how to troubleshoot a system. It doesn't matter whether they are Ford, Mopar, Massey, Kia or whatever as long as they understand the refrigerant on your system. And have the proper diagnostic tools and vacuum pump, micron gauge, vacuum rated hose, etc.

Only then should the system be tinkered with. You don't want to open the system unnecessarily, have to replace the dryer/filter, and triple-vac with nitrogen before charging. Cutting corners now will mean a blown system later.

 

[Tughill Tom]

With a High side press of 420 Psi my HVAC tech mind goes right to Non-Condensables in the system (I.E. Air). It needs to be Evacuated, Pressure tested and cleaned up and recharged by someone with HVAC background.
Just having a set gauges doesn't cut it!

 

[nota4re]

Before throwing any parts at it I would recommend a complete evac and recharge to the proper level before trying to diagnose.

Completely agree. This is really the only way to get back to the proper amount of charge as well as oil that should be in the system. As other have said, there's really no difference between other AC systems. The components, their function and proper diagnostic procedures are all the same. Automobiles are required to have a sticker stating the type of charge used as well as the system capacity. Tractors likely have this sticker too - when new. If it cannot be located, you may need to consult the service manual but once you have this, everything should be good.

 

[bunchgrass]

I just dropped off my old Dodge Ram that's also having AC issues at a decent shop that handles AC stuff. Owner - we can't tell you anything without emptying the system, pulling a vacuum and recharging to appropriate specs. Boom. Big difference. Maybe I need to trailer my tractor to him.

 

[bunchgrass]

With a High side press of 420 Psi my HVAC tech mind goes right to Non-Condensables in the system (I.E. Air). It needs to be Evacuated, Pressure tested and cleaned up and recharged by someone with HVAC background.
Just having a set gauges doesn't cut it!

The Kubota mechanic tried to look for bubbles in the sight glass on top of what I assume is the drier adjacent to the condenser. Outside in bright sunlight and that tiny sight glass --- I'm not sure what you could see.

When they attach a refrigerant tank to your system to add more, how do they purge air from the line so as not to introduce it into the system?

 

[Motronic]

When they attach a refrigerant tank to your system to add more, how do they purge air from the line so as not to introduce it into the system?

They shouldn't have to. The lines are sealed when you remove them. So the lines should be full of R134a from the last time they used them.

For what it's worth, even if they had nothing but air in them it's not enough to explain that high side pressure on its own.

Agreeing with the others that this system needs to be vaced and pressure tested and then have the correct charge weight put in to see how it acts before doing anything else.

 

[bunchgrass]

They shouldn't have to. The lines are sealed when you remove them. So the lines should be full of R134a from the last time they used them.

For what it's worth, even if they had nothing but air in them it's not enough to explain that high side pressure on its own.

Agreeing with the others that this system needs to be vaced and pressure tested and then have the correct charge weight put in to see how it acts before doing anything else.

I agree. Problem is I need the tractor now to bale ASAP and we're headed for ridiculously hot weather from Sat through at least Thurs ---mid 100's to 100 teens.

 

[Motronic]

I agree. Problem is I need the tractor now to bale ASAP and we're headed for ridiculously hot weather from Sat through at least Thurs ---mid 100's to 100 teens.

Any place with a robinaire or other automatic 134a machine should be able to do this for you. I'd call that shop that has your truck in for AC work and see if they can bring the machine out or you can bring the tractor in. They may not have a way to look up the charge weight, but that should be easy enough to find online in the service manual.

 

[moesfarm]

I have a M105X and a M8200. I like everything about Kubota's but there a/c design and there rough ride.

 

[GreensvilleJay]

If you can't get an 'auto mechanic AC guy', try your house HVAC service guy. neighbour did my F150 3 years ago,been fine since.... I'd rather have an HVAC guy on my machine than a 'tractor mechanic'...

None of my tractors or cabbed combine had A/C and I bet it was HOT decades ago, farmers still got the crops in. Lots of water and an extra fan will keep you 'somewhat' cool.

 

[Orange1forme]

Call it:
de minimis də mĭn′ə-mĭs″

• adj.
  
  Of little importance; insignificant.

Then it's okay.

Low pressure switch protects unit if it is too cold or low on refrigerant and the high side protects from too hot or overcharged(simply put, but with other factors playing contributing roles).

It is impossible to tell how much refrigerant is in a system by looking at gauges. That said if other things are not 100%, even a gauge reading means nothing.

The sight glass can be seen in just about any condition, if you know how. It should be clear/full of liquid when at normal operating condition. Some bubbles upon start up or at shut down are acceptable.

I would bet that the high pressure switch is cycling the compressor, based on the high pressure reading you gave. Being unsure of the proper charge and readings, I base that on general knowledge.

You need a tight belt to keep the fan turning at proper RPM, the condenser coil needs to be clean(since you are haying, I know you said it was ify before, maybe the radiator and coil are dirty/plugged) and the higher temps don't help.

 

[bunchgrass]

If you can't get an 'auto mechanic AC guy', try your house HVAC service guy. neighbour did my F150 3 years ago,been fine since.... I'd rather have an HVAC guy on my machine than a 'tractor mechanic'...

None of my tractors or cabbed combine had A/C and I bet it was HOT decades ago, farmers still got the crops in. Lots of water and an extra fan will keep you 'somewhat' cool.

Anyone who has used an enclosed cab machine (combine/tractor/feller-buncher) knows that running w/o AC in hot weather is nothing like running an open station machine under similar conditions. I also paid good money for this machine an expect it to perform as purchased. I'm not going to cabbage it together like other old equipment I own.