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Discussion Starter · #1 ·
The compressor has perfect pressure for high and low sides. There are no leaks, the pressure remains the same. The unit will heat but not cool. The conclusion is that the flow of the heat pump is not set correctly. In other words, there is a leak from the heat side that keeps the unit from cooling correctly.

The flows for the heat and cool side are adjustable after the cover is removed. There is ZERO information from Deere of how to set these adjustments. As you adjust these, because the cover is off, there is no air flow through the evaporator so it's impossible to tell when the adjustment is right.

There must be some way to set these used at the factory (but not ever correctly on our 4720). Please HELP
 

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Put a T-valve in the heater line to shut off the heat flow.

Dave
 

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Does the compressor actually turn on? You may have to check voltage at the compressor clutch to see if its being enabled.
 

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Discussion Starter · #4 ·
Compressor works just right at 275 over 50 at 95%. This is all about the heat side getting into the air handler. Good idea about closing the heat side. However, setting the air valves correctly would be better.
 

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Do you think it's air related or something in the controller for the hot water valve or the hot water valve itself? I would pull and plug the hot water hose just for a test to see if it worked. If it does then troubleshoot the water issue. If that doesn't work then you know you have an air issue. Does it cool at all?
 
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I would be pulling the roof off the cab and watching the heater control valve (B) while moving the heater control valve cable (E) with the heater control inside the cab. If the heater control valve is not moving to the fully closed position, it will allow hot water to circulate through the heater core which will heat the air going into the cab.

785939
 

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When the 3x20 and 4x20 cabs first came out, there was a huge problem with the seals in the roof, has it ever been off to inspect?
 
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Discussion Starter · #8 ·
I would be pulling the roof off the cab and watching the heater control valve (B) while moving the heater control valve cable (E) with the heater control inside the cab. If the heater control valve is not moving to the fully closed position, it will allow hot water to circulate through the heater core which will heat the air going into the cab.

View attachment 785939
I would be pulling the roof off the cab and watching the heater control valve (B) while moving the heater control valve cable (E) with the heater control inside the cab. If the heater control valve is not moving to the fully closed position, it will allow hot water to circulate through the heater core which will heat the air going into the cab.

View attachment 785939
Thanks. I had assumed, incorrectly, that this was a heat pump issue, where the flow is reversed for heat or cool, just like the HVAC systems used for homes. I had no idea that heat came from the coolant system. Next time I pull the cover, I'll run through the steps, and see in we can get the AC working. The wife is from Kansas, BTW, and running the 4720 in summer in Texas is hotter than hell. Probable just the same for you. She will appreciate getting this fixed.
Ted
 

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Thanks. I had assumed, incorrectly, that this was a heat pump issue, where the flow is reversed for heat or cool, just like the HVAC systems used for homes. I had no idea that heat came from the coolant system. Next time I pull the cover, I'll run through the steps, and see in we can get the AC working. The wife is from Kansas, BTW, and running the 4720 in summer in Texas is hotter than hell. Probable just the same for you. She will appreciate getting this fixed.
Ted
The system used is exactly like those used on a automobiles, no difference.
 
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Compressor works just right at 275 over 50 at 95%. This is all about the heat side getting into the air handler. Good idea about closing the heat side. However, setting the air valves correctly would be better.
Pressures are a little high. I read on another forum it's best to pull the battery to make sure you have the condenser clean. Wash out the radiator and condenser fins good and see if that helps.
 
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Discussion Starter · #11 ·
After removing the cab, there is no flow of the engine coolant into the system. It is fully closed when the heating knob in CCW, and has no leak. When the AC is started, there is some frosting of the evaporator. With the cab off, there is not air flow through it. The sealant appears OK around the entire cover. The filter and the evaporator are clean.
Dropping the cab back on, there is only a two or three degree drop in temp. Adding Freon up to 350 over 80 has no effect.
About the only remaining assumption is that the expansion valve, sensors for it, or the fixed orifice is stopped up.

What I really need is the full documentation of the AC system for the 4720.
 

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Dropping the cab back on, there is only a two or three degree drop in temp. Adding Freon up to 350 over 80 has no effect.
About the only remaining assumption is that the expansion valve, sensors for it, or the fixed orifice is stopped up.

Your low and high side pressures are too high.

You may have inadequate cooling / air flow through the condenser or your system is overcharged at this point. A plugged expansion valve would cause the low side pressure to be too low or go into a vacuum. An expansion valve that is stuck open could cause higher than normal low side pressure. If your system does actually use an orifice tube then look elsewhere for the issue.

Too much oil charge can also cause higher than normal high side pressures.

With the system operating at high idle (~1800 RPM) cool the condenser off with a garden hose and watch your pressures. If pressures return to normal and you get results (lower duct temperature) then check condenser airflow. Believe it or not I've actually removed and drained condensers of excess lubricant in the past to resolve operating pressure and lack of cooling problems.

Take a look at the attached temperature pressure relationship chart along with basic low & high side troubleshooting tips.

787659


787662
 

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Maybe I missed it but how's your air flow through the cab vents with the roof in place? Mine is loud with lots of air movement. Feel both sides of the filter dryer (I think that's on the liquid or high pressure side), if one side is cold it's probably packed up and acting like an expansion valve.
 

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After removing the cab, there is no flow of the engine coolant into the system. It is fully closed when the heating knob in CCW, and has no leak. When the AC is started, there is some frosting of the evaporator. With the cab off, there is not air flow through it. The sealant appears OK around the entire cover. The filter and the evaporator are clean.
Dropping the cab back on, there is only a two or three degree drop in temp. Adding Freon up to 350 over 80 has no effect.
About the only remaining assumption is that the expansion valve, sensors for it, or the fixed orifice is stopped up.

What I really need is the full documentation of the AC system for the 4720.
Now you have the system way over charged.

At this point you need to take it to a professional. They should have the proper equipment and knowledge to evacuate and repair the system.
 
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Here are the pages from the 3x20 CAB manual, the same cab is used on the 4x20 so it should be the same.
 

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Discussion Starter · #16 ·
Thank you for attaching the repair manual. After months of trying to solve this problem, I have concluded that it is an expansion valve problem. We can set any pressure ration from 140/40 to 325/130 with ZERO difference in cooling.

However, there is a small tube located about 2/3 of the way across the evaporator (left side), that runs to what seems to be a switch or relay. The tube appears to be a temperature sensor. This in turn, may control the expansion valve. We have to remove that cover again to troubleshoot how this connects to the expansion valve. This relay/switch does not appear on any documentation or parts list. Unfortunately, there is no information in these pages about the expansion valve or the evaporator. This section addresses testing, adjusting dials, and managing Freon and oil for the system. Maybe there are more pages, like for the initial assembly of the AC System during manufacturing.

I will take pix and post them.

Thank you again for the document. Beats $220 for the entire manual.
Ted
 

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That capillary tube most likely goes to the AL175777 temperature switch. It will also have a cable from the temperature control knob. I expect it senses when the temperature setting is achieved and cycles the compressor off until it warms back up then cycles the compressor back on.

Looks like your expansion valve bolts directly to the evaporator and the Freon lines attach directly to the valve.
 

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I'm tagging along.
Not because I have a cabbed tractor but Because I'm closing in on 8K into my Dodge trucks AC unit.

Its a must have for me.

This may or may not be related...But.....The Dodge system has 1 dumb small "air" door that when it malfunctions
will not let the truck cool as its pumping in air from the wrong spot.

Mine is showing signs of this issue after dealing with condensors,pumps ,clutches..etc. multiple times now.

The bad......This dumb door is deep in the dash........As in the fix starts with removing steering wheel/column...The entire dash......whatever 18 hours later and thousands to fix is in my future.
I'm hoping I can run a wire in somewhere and grab this door and get it shut for good when it finally fails.

Point is........Check that any Vacume or electricly operated vent/doors are doing what they are supposed to if so O equipted>
 

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Discussion Starter · #19 ·
That capillary tube most likely goes to the AL175777 temperature switch. It will also have a cable from the temperature control knob. I expect it senses when the temperature setting is achieved and cycles the compressor off until it warms back up then cycles the compressor back on.

Looks like your expansion valve bolts directly to the evaporator and the Freon lines attach directly to the valve.
Well thank you. This is the first info I've had about the expansion valve and it's control. So, the conclusion is that either the expansion valve is stuck, or the temperature switch in not working properly. Now that I see the switch, it directly operates a wire cable to control the expansion valve one way or another. We'll remove to top and see how this works. The compressor seems to keep running, as pressure is maintained. I'll come back and comment how this operates.
A description and a part number... It doesn't get any better that that. Thanks again.
Ted
 

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Well thank you. This is the first info I've had about the expansion valve and it's control. So, the conclusion is that either the expansion valve is stuck, or the temperature switch in not working properly. Now that I see the switch, it directly operates a wire cable to control the expansion valve one way or another. We'll remove to top and see how this works. The compressor seems to keep running, as pressure is maintained. I'll come back and comment how this operates.
A description and a part number... It doesn't get any better that that. Thanks again.
Ted
What makes you think that the system has a modulating expansion valve? I didn’t see anything like that on the parts breakdown, or no mention of it in the attached manual excerpt. I would think that it is like most automotive systems and just has a fixed orfice tube for an expansion device. That sensor on the evaporator is probably just to keep the evaporator from freezing up, and just drops the compressor when it gets near freezing. Automotive ac usually just runs full bore and cycles off the low pressure switch if it is a low load situation.
you can’t charge a 134a automotive system from the gauges…it is too damn touchy. Just evacuate and put the proper weight of refrigerant in and be done with wondering about charge. You have the pressure so messed up at this point you have to get the charge right before you can move forward. How are you going to know how much oil is in there also? I would want to flush and completely start over with oil/refrigerant.
 
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