Bummer - I think my AC Compressor is Failing!? (M7060)

[jjb01016]

Tractor: M7060 HDC12

Symptoms: A/C works fine and blows cold for about 20-30 minutes, then stops blowing cold. Next time i take out the tractor, the AC works fine again on startup, but after the same 20-30 minutes, it stops blowing cold again. If I keep the A/C on after it stops blowing cold, I noticed the engine temp starts to climb towards overheating after about 5 more minutes. If I turn off the AC, engine temp returns back to normal but usually the AC continues to blow hot if I turn it back on again. If I shut down the tractor and open the engine bay shortly after all this occurs, I do notice a burning rubber smell like a belt slipping.

Diagnostic work done so far: Low side and high side pressures checked, and are within spec (~22psi low, 180psi high side...probably a little low on R134A but plenty functional...). Condenser is clean and clear of debris.

I'm no AC expert but I'm pretty sure what is happening is that my compressor is on its way out, and after it runs for a bit and heat soaks, it starts to lock up - not completely, but enough to render the system ineffective. This also puts a big load on the engine, causing it to start overheating...and, some belt slippage occurs too which is what I'm smelling.

Here's a quick video i took of the compressor after the AC started blowing warm, and I think it shows exactly what's occurring. I have the AC on in this video, and I think it shows that the AC clutch is engaged but the compressor is ever so barely spinning. This is at idle.

Does this seem like the right diagnosis? A new OEM compressor is over $1000 so I don't want to spend the money unless I'm certain. The mag clutch itself is $800, so I think it'd be a waste to not replace the whole unit. OEM compressor P/N for my model tractor is RD451-93900

Also, I see some talk of skipping the OEM Kubota part and utilizing a Denzo SV07E unit, which is supposed to be the same OEM unit minus the Kubota/dealer markup. Has anyone here successfully gone that route? Here's the Denso part:
https://www.autoaironline.com/ac-parts/kubota-rd451-93900-ac-compressor-3152

Denso is a reputable aftermarket brand and probably the OEM supplier of the Kubota unit anyways. There are also knock-off units down around $200-300 but I'd rather avoid a no-name company.

Thoughts?

 

[Fedup]

Before replacing anything I would suggest you take a pair of vise grips and two large flat washers. Pinch off one of the heater hoses so there won't be any water flow. Run the tractor (A/C on) again for a half hour and see if that makes a difference.

What you're describing is a very common problem an many cab tractors. If the heater control valve fails to close completely the result is very often what you have going on.

 

[jjb01016]

Appreciate the response! Ok I follow and can give that a try, but would that explain the compressor behavior?

 

[whatsupdoc]

What are the pressures when the it stops blowing cold?
If you can access the tube to the inlet of the evaporator and connect
a remote temp probe onto the tube wrapped in insulation with the
meter in the cab.

The video seems to show the clutch slipping but it can also be a video
frame rate issue.

 

[Russell King]

You may want to clean the evaporator coil that is inside the cab. They supposedly get clogged up and that gives symptoms similar to your description (if I recall correctly).

The coil is under the headliner in some tractors and in others it is underneath the seat. (I have no idea which you have).

 

[jaxs]

It's hard to say whether clutch is slipping from watching video. Try sticking masking tape at 12-3-6 ad 9 o'clock on both outer and inner clutch hubs (precision not required). Use crayons,markers or such to color tape on inside hub 4 different colors and outside hub 4 other colors. That should help make an accurate assessment of whether clutch is slipping.

I'd call cold in neighborhood of 50f , hot 80f to ambient temperature. Leave gauges hooked up, if the problem is with flow of refrigerant, pressures will dramatically change. If a drop of moisture is collecting in metering orifice freezing, hi pressure will go through the roof and low will drop close to vacuum. A malfunctioning metering device could do the same so if pressures indicate, we can talk about how to narrow down between two and how to go from there.

Pay close attention to sight and sound of radiator fan. If it's suspect, place a large fan blowing through radiator. I use an old squirrel-cage from a gas furnace, the same one I drag around to circulate air in my shop.

Report back after trying this and what others have suggested.

 

[BAP]

Before replacing anything I would suggest you take a pair of vise grips and two large flat washers. Pinch off one of the heater hoses so there won't be any water flow. Run the tractor (A/C on) again for a half hour and see if that makes a difference.

What you're describing is a very common problem an many cab tractors. If the heater control valve fails to close completely the result is very often what you have going on.

First thing I would do is too follow Fedup’s advice. Out of our fleet of 14tractors, loaders, self propelled chopper and dump trucks we had on the farm with AC, I ended up putting a shutoff valve in 1 of the heater lines on 6 of them because the in cab heat control valve failed causing AC to shut down. The self propelled chopper, which at that time cost over $500,000, failed the first day we used it brand new from the factory. All I would do was go to the hardware store, buy a ball valve, 2 npt to hose barb fittings, 2 clamps. Cut one of the hoses and put the valve in. Open it in the fall when it got cold and close in the spring when it warmed up. Worked every time.

 

[Tx Jim]

Ditto on blocking heat hose from any coolant passing through it. Heater hose on my '91 JD 4255 has had heater hose cut-off valve closed since 1994.

Is radiator, condenser, evaporator & AC filters very clean from dirt/debris?????

Next one needs to attach AC gauges to determine if refrigerant pressures are in spec's.

 

[Old Machinist]

I've had the same thing going on to a lesser degree on my LX3310. I don't think it's a heater control issue since it cools as well as it does even after the engine temp has warmed up.

Mine will usually work fine as long as the tractor is moving but after it gets the least amount of debris in the condenser and radiator it will begin to lock up when I stop movement.

The other day I checked the air gap on the clutch and reshimmed it tighter but that had no effect. I also pulled the cab air filter and blew out the evaporator as best I could by aiming my leaf blower in through the cab vents. I also blew up in the air filter hole and a bunch of dust came out. I followed up with a new cab filter. I haven't done any mowing in extreme heat since but what I've done it hasn't had a problem since.

I have to clean my radiator and condenser after every mowing. After blowing out the screens and fins with a leaf blower I use a homemade version of the Lisle Radiator Genie. Their set has both a water and air wand. I would only use the water hose version. Get in around the fan and blow and wash from the rear as best you can. On my tractor there is room to get between the radiator and condenser to wash the condenser out. Don't ever use a pressure washer because it will bend the fins. Air pressure could potentially damage the fins also.

I think the condenser and fan volume on the Kubota is too small in both instances.

 

[GeoHorn]

Before replacing anything I would suggest you take a pair of vise grips and two large flat washers. Pinch off one of the heater hoses so there won't be any water flow. Run the tractor (A/C on) again for a half hour and see if that makes a difference.

What you're describing is a very common problem an many cab tractors. If the heater control valve fails to close completely the result is very often what you have going on.

That would not explain why the radiator-temp rises after 20 mins. If the heater were suddenly operational…the temp would DEcrease…not increase.

It seems to me your R134a is low. Service that first, then see what occurs.

 

[Shawn T. W]

The low side psi seems very low to me, if your needing A/C the ambient temperature should be high enough to be looking for double that psi ...

 

[jjb01016]

Thanks everyone for the replies! I really appreciate it.

I think based on all the feedback here and some more thinking about the issue over the weekend, my next step will be to hook up the gauges when this issue occurs again. I have the base readings mentioned in the first post, but I don't have any from when the actual issue occurs...I'll get them ASAP and it should help indicate what's happening. Second course of action would be to add some more R134A and just see if that solves the issue, since I agree the readings are a bit low. I have sealant-free R134A and a can tap, and I've added it before in my personal vehicles.

No argument from me that a failed heater valve could cause the lack of cold air, but I really don't think that's the culprit...as someone mentioned, it doesn't explain the sudden overheating of the tractor (but a locking-up compressor does!!) or the compressor behavior that's happening. But I'll keep that in my back pocket as another thing to test if I don't make any headway.

I cleaned out the condenser last night again, just to be sure it's free of any debris and I'll run the tractor again with my manifold gauges at the ready, and report back what I find.

 

[jjb01016]

Alright, ran the tractor for a bit last night. Sun down, 72 degrees F, so not exactly rough conditions for the system. No loss of cold air even after a good 40 minutes of use. I hooked up my manifold after things had been thoroughly heat soaked for those 40 minutes anyways, and here's what I observed. Much different readings than the first video I posted, when it was hot out (~85 degrees F) but the system wasn't heat soaked at all.

Obviously the compressor is short cycling here - seems like about 10 seconds between clutch engaging and releasing - and both high/low side readings are low. I was reading around 22psi low / 140 psi high pressure side just before the clutch released.

I'm pretty sure the system must just be low on refrigerant. And is that weird kinda locked up looking behavior of the compressor just the clutch slightly sticking and allowing some herky jerky rotation of the compressor when it's not engaged?

 

[Shawn T. W]

I'd say it's needs some Freon ... With the clutch starting and stopping so often I'd say that's what your smelling ...

 

[jjb01016]

Right right, I wonder if the clutch is getting hot and that's what is causing the drag!

Meant to post this too. Here's the snippet out of the M7060 FSM on low/high side pressures. It's missing any reference to ambient temp, so I also included one from the internet that does for R134A systems.

 

[chim]

Cleaning fins on the radiator and condenser takes more than a quick wave of the leaf blower. I routinely use compressed air to clean them. The jet of compressed air should be a more thorough method than a leaf blower. It wasn't until I did a more involved cleaning with water that I realized how much junk can hide in the fins:

My, What dirty fins you have

The goal today was to clean the radiator and condenser fins. Funny how tasks have a way of increasing in scope. It was a successful day though. What really surprised me was just how dirty the fins were. I do use compressed air and the two tools shown in the first/second photos and felt my...

www.orangetractortalks.com

 

[GeoHorn]

Alright, ran the tractor for a bit last night. Sun down, 72 degrees F, so not exactly rough conditions for the system. No loss of cold air even after a good 40 minutes of use. I hooked up my manifold after things had been thoroughly heat soaked for those 40 minutes anyways, and here's what I observed. Much different readings than the first video I posted, when it was hot out (~85 degrees F) but the system wasn't heat soaked at all.

Obviously the compressor is short cycling here - seems like about 10 seconds between clutch engaging and releasing - and both high/low side readings are low. I was reading around 22psi low / 140 psi high pressure side just before the clutch released.

I'm pretty sure the system must just be low on refrigerant. And is that weird kinda locked up looking behavior of the compressor just the clutch slightly sticking and allowing some herky jerky rotation of the compressor when it's not engaged?

Ignore for the moment) your conviction your clutch is defective. it’s behaving correctly as far as I can tell.
The Primary PROBLEM is your refrigerant is LOW.

Service it. Add a half-can or so of 134a and watch things settle down.

 

[jaxs]

Ignore for the moment) your conviction your clutch is defective. it’s behaving correctly as far as I can tell.
The Primary PROBLEM is your refrigerant is LOW.

Service it. Add a half-can or so of 134a and watch things settle down.

I agree, should he/we also ignore for the moment he said engine is overheating as a result?

 

[jjb01016]

OK, more fun tonight! Charged the system. No issues there, as I've done so before on other R134A systems.

AMBIENT TEMPS WERE AROUND 65F TONIGHT WHILE DOING THIS TESTING AND FILMING FYI!

Still having odd behavior post-charge:

- When AC system is set to "OFF" with the engine running, the compressor clutch is still. Zero rotation. High and Low sides settle to equal pressure as expected.
- When AC system is then turned "ON", the compressor clutch engages, AC operates as expected and blows ice-cold. Low and high pressure ratings are in the range of "normal" for a charged R134A system. But, after about 30 seconds, the compressor clutch disengages and the system starts to continuously short cycle. It basically seems to engage the clutch for 30 seconds initially, then disengages and re-engages and enters into this 5ish seconds engaged / 3 seconds disengaged loop.
- That initial disengagement after about 30 seconds of run time doesn't seem to be associated with a low-pressure min or high-pressure max trip - as you can see in the video below at approx 1m:00s, the compressor clutch drops while the low side is around 30psi and the high around 150psi. Those are normal readings for R134A system at 65F ambient temp.
- When the system disengages the compressor clutch with the AC 'ON", the clutch drags a little bit. That's the slow herky-jerky action you're seeing in the video. As mentioned in the first bullet here, there is zero rotation of the compressor when the AC is set to "OFF"

So I'm thinking it definitely was low on refrigerant (which we all already knew from the previous gauge readings...) but there seems to be a problem with the compressor clutch or the control system for triggering it. Does that seem right, and any guesses on what to look at next?

One other note. The factory manual has what may be some incorrect info in it with respect to the low pressure side min pressure switch...it seems to indicate less than 28psi will trip the low pressure switch, yet the factory low pressure normal range is 22-28psi? This seems odd?

 

[jjb01016]

I think before I condemn anything based on the above, I ALSO need to hook up the gauges again when it's hot out tomorrow during the daytime. I'm wondering if the cool temps (65F, after dark....no sun...) are what's causing the short cycling...