Automotive Air Conditioning Information Forum

Kubota farm tractor does cool, just not well. Both low side and high side pressures are higher than normal. High side will approach 300 psi possibly more. The low side was maybe 60 perecent higher than it should be.

Unit is not over charged in fact it’s undercharged by about 60 percent. Unit has been pulled down and charged from a vacuum.

I have not veirified this but dealer tells me 5his unit has an expansion valve not an orifce tube. It is 134.

Condenser is clean as is the evaporator and both have good airflow. Belts are tight.

A like machine will cause you to lower the ac settings as it gets quite cold.

Ideas?

"maybe 60 perecent higher than it should be."
Please give exact pressure readings, and RPM at which taken.
Any chance you can give Model and year

" in fact it’s undercharged by about 60 percent."
How do we know that

Ok, but when you say vacuum, what do you mean? Edward's $5000 vacuum pump, professional micron gauge, pulled her to 500 microns, triple evac, break it with R134a each time? (Way overkill )

OR

Harbor freight compressed air venturi pump, 10 minutes, squirt the refrigerant.

OR hopefully something in between?

I ask because poor cooling capacity AND high condenser pressure means air in the refrigerant or poor condenser airflow or fins clogged with chaff. You've said clean condenser, good airflow.

Edit: Now that I think about it, are you running only 60% of the charge because the condenser pressure is too high with full charge?

Correct 60 percent of factory spec charge because of high condenser pressures. Factory charge is 2.2 lbs I have approx 1.3 in the unit now.

just about all my a/c tools are robinair.

Recovered and charged at least three times to discount air/moisture the in system.

I’m leaning towards a bad expansion valve or sensing tube issue. Haymaking season is here so it’s hard to get the machine into the shop. Not ruling out blockage at some point though either. Lines snake every which way.

It does use an expansion valve.

Pressures on the order of low side 45 high side 300 At 600 rpms. Higher engine speeds yield higher head pressure. 82 degrees outside 65 percent humidity. 60-65 at center vent. A like unit is difficult to use with the a/c set to high because of low temps in cab.

It’s a 2000 kubota M9000 with lower hours.

Why are you undercharging it, factory unit? I don't worry about 300psi, if on the high side.

When you were charged with 2.2lb, what was the high side pressure?

Tim wrote: ↑Thu Jul 08, 2021 12:51 pm Why are you undercharging it, factory unit? I don't worry about 300psi, if on the high side.

Because with a full charge at working engine speeds high side pressures are very close to 375psi. I’d prefer not to need replacemnet parts because of a blowout. System vents excess pressure in that area 385 I think.

Factory system. Who knows what some shade tree mechanic may have done to this system and or put in it.

Hello,

I'd like to know what your high side pressures settle down to with a little water sprayed / misted onto the condenser fins. I'm thinking the fan is not moving enough air for you through the condenser fins and tractor radiators are notorious eaters and lodgers of grass seed husks.

My prediction is that your high side pressure will fall like a meteor and you will need to consider adding refrigerant after cleaning your radiator / fan / fan clutch, etc.

Rick

Radiator and or condenser are spotlessly clean.

What is the fan? Direct drive from the engine? Back edges sticks out of the shroud the same as your reference good tractor?

If your airflow is good and your condenser airside is good and clean, I'll have to say again that you have air in there. A non-condensable gas can just sort of hang out in the top of the condenser, and just occupy tubes, giving you a much smaller condenser, like imagine this tractor has a condenser 3/4 the size of the good tractor. The only way such a condenser can reject all the heat you are adding is to go to a higher temperature, i.e. a higher pressure.

I've known technicians who work on A/C for years just assuming air in hoses, manifolds, recovery cylinders just magically gets purged, or that it really doesn't matter. A Robinair unit will actually do a lot of air purging from hoses and recovery bottle and reinforces this impression that air in the hoses does not matter.

Does this refrigeration system leak? If you try to pull a vacuum on a leaking system you'll be sucking air in until you start adding the refrigerant and get the pressure above ambient pressure. I've seen compressor shaft seals that work perfectly well until there is a vacuum and they will leak and let air in.

It's also possible to have way too much oil, kind of acts the same way, displaces refrigerant, degrades heat transfer.