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Tractor Talk Discussion Forum

Kubota AC Repair

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psbhouston

07-10-2014 10:09:05
64.253.68.106



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I could use some advice. I have a Kubota M9540. The evaporator in cab was plugged. Cleaned it out and now it blows strong air thru the system. I hooked up manifold gauges and both Low/High side pressures were too high. (50/350).
I am sure that one of my guys added freon in the field and overcharged and introduced air into system. I evacuated the system and checked for leaks. None noticed. The systems holds 1.87 to 2 lbs of R134. I charged it with about 20oz and pressures are already back to 40psi Low / 280psi High. Air temp at vent is 67degrees so its cooling a bit - but what am I missing?
Manual says clean condenser / check "heat sensitizing tube and expansion valve??? What is a heat sensitizing tube?

I thought expansion valve would not cause high pressures on both sides? But - I know only enough to be dangerous. Need help please - don't want to kill the system.

many thanks

Greg

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Mark Robke

07-11-2014 18:36:18
71.31.17.252



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 Re: Kubota AC Repair in reply to psbhouston, 07-10-2014 10:09:05  
I am not familiar with your Kubota, so I don't know if your condenser uses an electric fan or uses the engine fan. But first off=idle your engine up to 1200 rpm or so, hold a rag up to the front of condenser.The rag should suck up to the condenser all across the the face- move the rag all across it. If it does not draw the rag up every where, clean it/fix fan problem.If you have poor air flow and the condenser looks clean, you can have dirt between the radiator and condenser and/or the charge air cooler. You have to separate them to clean. This would be causing high head pressure. Even with a properly charged system, high head pressure will cause hi suction side pressure, and, poor cooling because you are not getting rid of the heat absorbed because of poor air flow across the condenser.
Air in the system usually causes only high head pressure and normal low/suction side.Poor air flow thru the evaporator should cause low suction side pressure.
If your air flow thru the condenser is good, and your pressures still read high, I would change the expansion valve(or the orifice tube) and THE DRIER.If you did have air in the system a new drier is a must.It is possible to have an expansion valve stuck open, but this should mostly cause high low suction side pressure.I would guess you have a block style expansion valve which are the simplest/most common style used.
Mark

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MSM

07-10-2014 14:21:55
70.192.207.32



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 Re: Kubota AC Repair in reply to psbhouston, 07-10-2014 10:09:05  
I would replace the expansion valve, it seems it is partially clogged causing your high pressures. The heat sensing tube is a small somewhat flexible tube that is imbedded between the fins of the evaporator. It senses the temp of the evaporator and adjusts freon flow through the expansion valve so the evaporator doesn't freeze.



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jm.

07-10-2014 12:29:47
162.72.81.167



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 Re: Kubota AC Repair in reply to psbhouston, 07-10-2014 10:09:05  
PSB Go right behind the seat little box that looks like a briefcase. Remove that cover and clean the filter. You are not moving enough air. Think that will solve your pressure problems since you have done such a good job on the rest. Most folks don,t have gauges and just do as you say your guys did and load the system without cleaning or checking anything. Let us know the results.



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psbhouston

07-10-2014 12:48:04
64.253.68.106



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 Re: Kubota AC Repair in reply to jm., 07-10-2014 12:29:47  
jm

I have cleaned the evaporator and all of the cab duct work. What a mess. It is a poorly designed system that had leaks on the duct work on fresh air and recirculate systems. I sealed it all up with foil back tape and now only clean air is going thru it. It blows hard and there is a lot hitting you in the face.

For giggles - I blew out the condenser up front with compressed air. It seemed clean. But I decided to run water over it while the manifold gauges we hooked up.
The pressures dropped to 40 and 190 psi and the vent temp dropped to 62 degrees. I will let it all dry and see if it holds but I would bet the pressures head higher up.

The book calls for low side 21/28 and high side 185/242 psi.

will let you know - have to get the hay on the ground - but dont want to cook while doing it.

thanks for your advice

Greg

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jm.

07-10-2014 14:56:41
162.72.81.167



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 Re: Kubota AC Repair in reply to psbhouston, 07-10-2014 12:48:04  
OK Been selling Kubota 30 years old 9000 series were a mess but your 40 series has not been troublesome at all. I think you have found your problem. The worst thing you can do is put water to the condenser. All those seed and dust turn to mud and swell. You solution now is to take small flat shipping strap and slide it thru the condenser and get back with the compressed air. Get the flow of air in there and your pressures are going to level out. The 65 deg discharge is not hardly there but something like 35 degrees below the outside temp is a starting place.

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psbhouston

07-10-2014 12:47:41
64.253.68.106



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 Re: Kubota AC Repair in reply to jm., 07-10-2014 12:29:47  
jm

I have cleaned the evaporator and all of the cab duct work. What a mess. It is a poorly designed system that had leaks on the duct work on fresh air and recirculate systems. I sealed it all up with foil back tape and now only clean air is going thru it. It blows hard and there is a lot hitting you in the face.

For giggles - I blew out the condenser up front with compressed air. It seemed clean. But I decided to run water over it while the manifold gauges we hooked up.
The pressures dropped to 40 and 190 psi and the vent temp dropped to 62 degrees. I will let it all dry and see if it holds but I would bet the pressures head higher up.

The book calls for low side 21/28 and high side 185/242 psi.

will let you know - have to get the hay on the ground - but dont want to cook while doing it.

thanks for your advice

Greg

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Allan In NE

07-10-2014 10:43:26
199.47.66.61



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 Re: Kubota AC Repair in reply to psbhouston, 07-10-2014 10:09:05  
Replace the filter or screen. Too low on the low side and too high on the high side.

Things aren't moving in there.

Allan



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psbhouston

07-10-2014 10:58:58
64.253.68.106



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 Re: Kubota AC Repair in reply to Allan In NE, 07-10-2014 10:43:26  
Thanks Allan,

When you say filter or screen - is that at the drier or receiver?

I am not sure if the manual shows it in my book.



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psbhouston

07-10-2014 11:04:51
64.253.68.106



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 Re: Kubota AC Repair in reply to psbhouston, 07-10-2014 10:58:58  
Allan

A note to add to info: I pulled the condenser slide out to make sure it was clean. When I did the low and high pressures went nuts. The high pressure switched kicked and it started to rapid cycle. AS soon as I slid it back into place - it all went back to 45/275 psi. Hoses were not kinked our twisted when the slide was out - at least I don't think so

thanks



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