M7040 - AC works but blows hot after a while

[btcfarmer]

You mentioned that there was no oil in the compressor. It is possible that the oil migrated to the condenser or evap. If you have excess oil in the system, it could affect performance as it it like an extra layer of insulation inside the tubes.

No, there was little oil in condenser and evaporator. What was there was what i added myself when i replaced the evap earlier this year.

I am now certain that the previous owner ran it with the broken evaporator for a long time and squeezed 95% of the oil out through the hole it had in it.

Someone said higher up in this thread that if he was working on a used tractor with a compromised evaporator, he would have pulled everything - compressor, condenser, evaporator, gone through each part and made sure each was clean and had the right amount of oil in it. That's what I should have done, and am doing now.

 

[btcfarmer]

I hope that you have changed the expansion valve and put on a new drier. If not, change them before putting it back together.

Yes sir, I neglected to say so above, but I also replaced both of these components, and added thr prescribed amount of oil to the new drier (going by kubota wsm).

 

[btcfarmer]

For the record, if someone needs to do this full system clean out / recharge, here's the correct amount of oil (PAG46) to use for the m7040, as per kubota wsm:

Compressor: 120ml
Condenser: 40ml
Drier: 10ml
Hoses: 10ml
Evaporator: 40ml

And around 2lbs of r134a refrigerant.

 

[jaxs]

First, apologies for the very slow response, and thanks for your reply.

I think you are right about the compressor being to blame. I have cleaned the whole system meticulously, and I have pinched the heating coolant hose, and I have verified no icing going on at or near the expansion valve.

I believe the compressor is indeed slipping. It turns over just fine when I first start the tractor up, but once it starts blowing warm air, I can see how it resists turning over, and stalls out for brief (0.1-0.2 seconds at a time), causing the wheel to get extremely hot from all the friction of the belt sliding across it instead of spinning it.

Meanwhile checking the gauges, I see that the pressure never gets much higher than ~210 psi.

I have a new compressor sitting in my workshop, and I am going to install it tomorrow.

Thanks for your help!

Are you positive the belt slips or is it possible clutch is slipping? I can't recall having a compressor locking momentarily and intermittently. Was belt smoking? What you describe is classic behavior of a failing clutch. Did replacement compressor come with new clutch?

 

[DustyRusty]

I don't know how Kubota instructs to add oil, but on the old GM R-6 compressor, I would add all the required oil to the compressor and after the system runs for a while, it would disperse the oil to the various components.

 

[btcfarmer]

Are you positive the belt slips or is it possible clutch is slipping? I can't recall having a compressor locking momentarily and intermittently. Was belt smoking? What you describe is classic behavior of a failing clutch. Did replacement compressor come with new clutch?

The compressor clutch was engaged the whole time. When the tractor was cold it looked fine, compressor turning over and not getting hot. This is when the ac would work somewhat (still not great performance, would yield at most 10-12 degrees relative coldness) from ambient.

When the tractor got hot, the compressor clutch stayed engaged, and would intermittently prevent the belt from pulling it, yes. It would resist, and this made it so hot I actually burned my finger tip touching it. Får hotter than other pulleys driven by the same belt.

I did at first think it was a clutch issue too, but it really wasn't - the pulley was definitely being arrested intermittently like I described.

After taking belt off, I checked how hard it was to turn the compressor over ny hand. Definitely quite hard and non smooth. Night and day difference compared to new compressor, after adding oil to it.

 

[btcfarmer]

I don't know how Kubota instructs to add oil, but on the old GM R-6 compressor, I would add all the required oil to the compressor and after the system runs for a while, it would disperse the oil to the various components.

I could not find any official instructions from kubota on this, but from my own research it seemed pretty clear distributing it yourself was the way to go.

Also, the whole system calls for about 8 oz of oil. I think the compressor is rather full after the 4 wsm prescribes - I had to crank it by hand for each ounce, and I think it was about to start overflowing from output orifice after that.

Plus makes sense the system would like it best distributed, no? The oil gets absorbed into the refrigerant under high pressure and travels with the refrigerant throughout system as I understand it. Does not seem like it would benefit it to start with all of it in the same place?

What my youtube research also revealed was it is crucial to handcrank the compressor at least 20 times before starting tractor when it is newly installed, or else it could get oil-locked and resist turning over and break. This seems like more of a risk if you put all the oil into the compressor only.

 

[btcfarmer]

Update: got a good compressor installed, and the system is now consistently cooling 30 degrees F relative to outside temp, and that is even when running it hard, in the Florida sun, for hours. Life's good.

 

[jaxs]

 

[Tx Jim]

I've never needed to repair my '11 Kubota M7040 AC but on my JD 4255 when I R&R compressor several yrs ago I just put required amount of oil in compressor only then installed refrigerant & AC system cooled very good.