Excavator a/c

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H8theheat
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Joined: Fri Apr 03, 2020 3:37 pm

Excavator a/c

Postby H8theheat » Fri Apr 03, 2020 4:09 pm

I am working on an doosan 140 lc-v excavator at work trying to get some cold air out of it. The compressor has been replaced it is a nippondenso model 10 pa and uses 134a. The system uses a txv as well as the condenser mounted behind the cab with an electric fan to cool it....heater valves are shut.

Flushed system first, added 7 oz of page 46 oil for new compressor...then vacuumed it down and it held for 25 mins...it got a new drier, cleaned condenser. Charged to 31 oz. ( Per doosan dealer) and it was blowing 65 out of the vent low side pressure was 10psi on the low side and 200 high side on a 75 degree day.

Did some research and seemed the expansion valve could have been sticking or stuck ( the spring didn't have tension on it like the new one ) , so I replaced it and vacuumed it down and charged again...now it will freeze u out in the morning 39-40f out the vent 10 psi low side and 170 ish high side in the morning 70 degrees outside...

As the day goes on the vent temp warms to 55-60 and it doesn't keep the cab cool...low side pressure is once again 10-15 psi and high side will be around 200 for an 80 degree day....

The high side seems good but why is the low side only at 10 psi ?? When the compressor comes on it stays on for about 18 seconds and then it cuts off for 40-45 seconds...I am wondering if I got a bad expansion valve and it is starving the low side ??
Al9
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Joined: Tue Mar 10, 2020 3:26 am

Re: Excavator a/c

Postby Al9 » Sat Apr 04, 2020 2:15 am

1)25 minutes is too short of a vacuum. Vacuum for at least 1 hour.
2)Condenser can't be flushed if parallel flow. Must be replaced in that case. Did the old compressor seize up?
3)Suction pressure is abnormally low. Sounds like the evaporator is being starved of refrigerant, provided it isn't freezing up. Which could point to 2).
4)Springs tend to deform and lose tension over time. Happened with my car's thermostat. Possibly happened with my TXV too since it's taking a longer time to bring suction pressure down (can be either a worn compressor or a marginal TXV) and hence "bring the cold" out. Unfortunately, in my case the original TXV is no longer available and sourcing an equivalent one is a hard task (and possibly an expensive one if you get the wrong one and you have to test another) since it's a variable displacement compressor.
5)Does vent airflow drop down as the air gets warm? The abnormally low suction and increasing vent temperature could also be an evaporator that is freezing up due to a bad evaporator temperature sensor (TXV system, so it's supposed to cycle the clutch depending upon evaporator temperature).
6)Where is the refrigerant port you're using to take the high side pressure located? Before the condenser or after it?
H8theheat
Posts: 9
Joined: Fri Apr 03, 2020 3:37 pm

Re: Excavator a/c

Postby H8theheat » Sat Apr 04, 2020 3:28 am

2 The bearing on the pulley seized up and was easier to replace the compressor.

4 expansion valve is brand new but I know it's possible it could be defective.

5 air flow is great at all times and evaporator fins were cleaned

Both high and low side ports are on the back of the compressor.

I pulled a belly pan yesterday and I could see where the lines run into the floorboard before they enter the expansion valve/evaporator....big line was 57-62 degrees and small one was like 72-75 degrees with system running don't know if this helps but it's more info.


I know I have a problem somewhere but what should the low side read theoretically for a properly cooling system ? Everywhere I have read about low side pressures it has to do with orfice tube systems and not txv should they run roughly the same pressures ?
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bohica2xo
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Re: Excavator a/c

Postby bohica2xo » Sun Apr 05, 2020 9:01 am

A 10 psi suction with a suction line temperature around 60f would indicate a starved evaporator.

Either a bad TXV, plugged capillaries in the evaporator, a plugged receiver or a damaged liquid line.

Since you indicate a clean system, with no compressor failures the evaporator is likely clear.

Is the new receiver / dryer installed with flow in the right direction?

Have you checked the liquid line for damage? Excavators get used hard. A rock can flatten a line with ease.

Where any restriction is, there will be a cold spot in the liquid line. Check the dryer and liquid line for cold spots by feel.
H8theheat
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Joined: Fri Apr 03, 2020 3:37 pm

Re: Excavator a/c

Postby H8theheat » Wed Apr 08, 2020 4:04 pm

There was a small kink in the liquid line it made a small difference when I straightened it...

I had to take the evaporator back out for this and while it was out I took every line loose and blowed through them , they all flow freely...even blowed through the drier it flows free too....blowed through the evaporator ( took expansion valve off ) also blowed fins clean but they weren't dirty really and blowed through the condenser and nothing is blocked....drier is installed with flow arrow in the right direction. Vacuumed the system back down and recharged...

now at 85 degrees ambient at idle, low side reads 25 and high side reads 200 roughly 46 degrees at vent...at full throttle which is what it runs at most of the day low side is 12 and high side is 200 vent temp is around 55 degrees

Isn't there a way to measure the temp before and after the expansion valve and or the condenser and it should be cooling x amount of degrees or else the valve needs adjusting or is bad ??
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bohica2xo
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Re: Excavator a/c

Postby bohica2xo » Wed Apr 08, 2020 7:23 pm

Sure looks like the TXV is starving the evaporator.

You said you replaced the TXV. I have run in to issues where the Heavy Equipment cross reference was not terribly accurate before.

What type of TXV does this excavator have? Block type or in line with capillary tube?

It could be a bad valve, the wrong valve, or an adjustment - not all valves are easily adjusted.
Al9
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Joined: Tue Mar 10, 2020 3:26 am

Re: Excavator a/c

Postby Al9 » Thu Apr 09, 2020 1:32 am

Agree - definitely sounds like the valve superheat is too high for some reason or its orifice is a bit smaller than intended and as a result tonnage is lower than required. In fact many automotive TXVs are specifically designed so that the evaporator never gets starved during the cycle, even at really low heat loads where the TXV tends to close the most, getting so far as specifically engineering the power head's charge so that superheat goes 0 at low enough suction pressures (you get this effect by basically loading the power head up with a mix of gases rather than the system's refrigerant) and the orifice basically goes wide open flooding the whole evaporator up and keeping suction pressure up, and closer to what you would expect from a 32F cold evaporator (on a side note, this has been even used with some fixed displacement piston compressors, so i think the resulting saturated refrigerant flow won't harm the compressor), and if the only restriction in your system is the TXV, then the opposite is what's definitely happening, especially since you're now getting a reasonable suction pressure value at the compressor (the one at the evaporator's outlet is a little higher depending upon the suction line's lenght) but only at idle. If you notice a spindle on the TXV, don't even think touching it, unless the manufacturer specifically instructs you to. You have to get the right expansion valve.
H8theheat
Posts: 9
Joined: Fri Apr 03, 2020 3:37 pm

Re: Excavator a/c

Postby H8theheat » Thu Apr 09, 2020 4:01 am

It is a block style no capillary tube, but there is a allen head cap at the bottom would this be the adjustment ??

I did keep the old valve and I just took the Allen head cap loose and there is and o ring then the tension spring...I guessing it it non adjustable because if I loosen the hex cap I'm sure the o ring will leak refrigerant ?
Last edited by H8theheat on Thu Apr 09, 2020 4:48 am, edited 1 time in total.
Al9
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Re: Excavator a/c

Postby Al9 » Thu Apr 09, 2020 4:22 am

You mean this one? As i said before, don't touch it.

If you touch it, you've basically tampered with the valve and you won't be able to return it. You might also ruin your compressor.

Aside from cross-charge power heads, superheat is a really complex thing in MVAC. Your suction line needs to travel in a hot space and the compressor still needs some cooling, both to last and to perform well, but letting it suck in slugs of liquid refrigerant (rather than mere droplets) all the time will damage it. Again, don't touch it. By the way, i bought this valve to play with (not use it in any vehicle at all), and while playing around with it, i noticed that if you turn the nut clockwise it will basically snap shut as soon as you get freeze spray on the disc. Turning it counterclockwise on the other hand will make the valve never close at all. The setting it originally came with allows a whisper of air to get through the orifice even once you've brought the disc to temperatures well below 32F. So yes, it's an adjustment, but it's not advisable to tamper with it, since we're dealing with stuff that is much more complex than residential AC.
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H8theheat
Posts: 9
Joined: Fri Apr 03, 2020 3:37 pm

Re: Excavator a/c

Postby H8theheat » Thu Apr 09, 2020 4:49 am

That's the exact valve !!!
Last edited by H8theheat on Thu Apr 09, 2020 5:34 am, edited 1 time in total.

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