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I found that you can have perfect high and low side pressure and the AC won't cool. The first thing to do is replace the filter next to the engine coolant.(#1 on the first drawing). Shop around, you can find one in Auto supply places for $10-$15. Follow up by cleaning ever filter or air flow area. Then you will have to evacuate and recharge to the correct high and low side pressure based on the outside temperature.
Attached is the pressure chart for 134A.

Also for those who don't believe, the 4720 Cab does have an expansion valve. It's located on the side of the box holding the evaporator. I've attached the pix of the unit.
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This may be the issue by theory......dealer had replaced the compressor....when I first got it it wasn't cooling well at all....put Gages on it and pressures were low on both sides....added freon till the high side got closer...low side seems still low....might be time to change exp valve and recharge by weight.....do you happen to know correct charge weight...I have seen two different #s in documents.....its easy for me to suspect dealer didn't pull the lid and called it good
Not offhand but it's likely less than 2 lbs. I usually charge based upon the Temperature - Pressure chart and observe the sight glass if equipped. Been doing that for years since I started servicing Thremo King and Transicold refrigerated trailers back in the day.
 
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This may be the issue by theory......dealer had replaced the compressor....when I first got it it wasn't cooling well at all....put Gages on it and pressures were low on both sides....added freon till the high side got closer...low side seems still low....might be time to change exp valve and recharge by weight.....do you happen to know correct charge weight...I have seen two different #s in documents.....its easy for me to suspect dealer didn't pull the lid and called it good
The technical manual I have for the 4520/4720 says that the system holds approximately 2 lb. 12 oz (2.8 lb) of R134A and 8.2 oz of TY22025 refrigerant oil.
 

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The technical manual I have for the 4520/4720 says that the system holds approximately 2 lb. 12 oz (2.8 lb) of R134A and 8.2 oz of TY22025 refrigerant oil.
System refrigerant capacity is more than I expected @ 2.8 lbs.

Just a comment about oil capacity. Never add refrigerant oil unless you're flushing the system or replacing a component. All too often systems that have been serviced multiple times are also overcharged with oil as well. The surplus oil ends up in the condenser and negatively affects heat transfer.

Unless you have a component failure or a burst line and see significant oil loss err on the side of caution.
 

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Also for those who don't believe, the 4720 Cab does have an expansion valve. It's located on the side of the box holding the evaporator. I've attached the pix of the unit.
Yup. My 3720:
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Kenny, were the green o-rings the replacements for the black o-rings in the first photo? Interesting that there were black o-rings installed as R134a systems usually use green.
I don't remember now Frank, sorry. Those pics are from July of 2017.
 
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Yup. My 3720:
Same as my 4066r I was having trouble with, pretty sure it was a stuck TXV which cleared
itself????
Been working OK enough for a couple of weeks, 23* split from ambient temp.
Still concerned however because Deere modded the TXV with an extra input.
A heavy black rubber hose running across the center of the control head, (drew it in on
the photo).
There is even a notch cut into the foam insulation to hold it against the TXV control head.
I'm assuming it's there to additionally modulate the block TXV for some reason like the older
bulb controlled TXV's.
Have inquired with dealer and Deere as to its' purpose, so far no answers.
Tech. manual and parts list do not show it
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Also found the Deere temp./pressure specs. in tech. manual seem to be a little off
from specs. on other R134a systems.
If anybody is interested will include the Deere tech. manual specs and the readings I get.

My last readings a month ago:
07/10/22
RPM = 2000
Low pressure = 25 PSI
High pressure = 210 PSI
Inside vent temp = 62*
Ambiant temp = 85*
Split = 23*
Static pressure after 30 minutes
Low = 95 PSI
High = 105 PSI

Deere tech manual info:

head.
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