[Superglidesport]

Generally a system that uses a fixed orifice tube has a pressure sensing compressor clutch cycling switch used to regulate pressure and evaporator temperature.

Usually with a system that uses an expansion valve the compressor remains on and orifice aperture changes to adjust pressure and subsequently regulate evaporator temperature.

Before servicing a system I attach gauges and monitor system pressures against ambient temperature and humidity. More often than not I will charge a system based upon gauge readings and system performance rather than dump and refill. Especially when I have access to a sight glass to monitor liquid line conditions.

If I'm not mistaken another member did have an AC problem at one time and I was surprised to learn that his late model 3 Series cab used an expansion valve and not a fixed orifice tube.

Just checked and here's the expansion valve listed for a 4720 cab. #18 below is definitely not a fixed orifice tube.

 

[Old Machinist]

The only correct way to charge is to KNOW what the factory specified charge is and start from a vacuum. Forget about using a sight glass as an indicator. According the the PDF provided by Kenny this would equate to about 3-1/2, 12 ounce cans. If it were mine I would drop 3 cans in and call it a day.

When I rebuilt the AC system on my New Holland backhoe I couldn't find that information. It has that same wonky little expansion valve shown on the JD. I installed a new expansion valve and compressor, flushed the system and blew it out with dry nitrogen, vacuumed to 30 inches for a couple hours, washed all the dirt out of the evaporator and condenser, and started charging. By the time I had three 12 ounce cans in it my gauge readings were heading for the sky and my sight glass was still solid foam. I finally got my hands on a manual with the specs and found out it only takes 1.65 lbs. I evacuated the system again and put two 12 oz cans in. Works as good as it can work in a glass oven. I may tint some day but that is another topic.

These are old school systems adapted to use 134a. The thermostatic control will sense the temperature at the evaporator and cycle the compressor on and off to control it. The colder you set the control at the knob the longer the compressor will stay on. Set all the way cold it will most likely never turn off unless it freezes. Any condition that prevents it from getting cold will result in the compressor running non stop as long as it isn't under charged.

Most systems will have a low pressure switch on the drier to cut power to the compressor if the pressure gets to low. I have never seen a system that regulates temperature by monitoring pressure. Pressure monitor switches are just to protect the components from damage in the event of a high or low pressure condition. I don't think I've ever seen a high pressure cut out either but it would be a good idea if they had one.

I'll give you a tip on charging using cans which is what most DIYers will have access to. NEVER feed the charge as a liquid. Shooting cold liquid into a hot compressor can, and will damage it. Keep the can upright with the valve at the top. This can take forever and sometimes never finish without warming the can. I use a 4 cup measuring bowl full of warm water to warm the can as I charge. Swish the can around in the warm water until to see the low pressure gauge drop indicating all the Freon is out of the can. If you are in question you can turn the low side valve off to see if it still drops. If it does drop with the valve off then open it back up and continue to change the water with warm to force it to gas out of the can.

I'm a little out of touch with modern systems but I was a Certified Master Auto Tech from the 70s through the 90s before changing my career path. We were just getting into the 134a era back then and most of what I was doing was flushing and retrofitting older R12 vehicles.

 

[Superglidesport]

I have never seen a system that regulates temperature by monitoring pressure.

Hundreds of Millions of CCOT (Cycling Clutch Orifice Tube) Systems used by most auto manufacturers do just that. A low side pressure sensing (cycling) switch turns the compressor on / off to control compressor duty cycle, high side liquid line pressure, low side vapor pressure and subsequent evaporator temperature. And, as you're likely aware, Pressure = Temperature.

Here you go:

Further explained here:

Over the years I've had the opportunity to support warehouse refrigeration systems and some commercial HVAC and chilling equipment. Maintained and repaired AC and refrigeration equipment on trucks, cars, busses and trailers. Diagnosis started with the basics, using gauges, pressures and a vacuum pump to test system integrity. Beyond engine, motor and / or component replacement system performance was restored solely by charging based upon operating and differential pressures. Sure, a novice can dump and recharge based upon a volume spec but it takes someone who knows what they're doing to make it work "properly" by the numbers.

 

[Ted Gage]

Problem Solved...

This system is NOT a heat pump design. There is a separate evaporator for the heat. And YES, there is an expansion valve hiding on the right side of the evaporator. I ordered and installed a new expansion valve. No difference.

Finally, I went to the John Deere dealer in Weatherford Texas and talked to the AC tech named Troy. We went through the proper settings, charge, and details. As we were finishing up, Troy said he recalled a factory error where they had failed to install an O-ring in the AC System, that the dealers were notified, installed the O-ring, then recharged the AC. However, if the period was too long the filter would start to clog up. Troy remembering this as the last minute was an eureka moment.

Rather than pay John Deere for > $120 for a filter, I purchased one from PitStopAuto for $32. Evacuated the system, removed the old filter, and also tested air flow through the evaporator. The system had to be stopped up somewhere. Now installed the new filter, evacuated the system, charged R134a to 250/30, tested for leaks, and suddenly the return temperature back to the compressor was 40 degrees. WOW.

So, from the beginning, this was a factory manufacturing error. There is no reporting information of this problem. The 900-page System Repair Manual has no AC information except for the proper amount of R134a, oil, etc. There is ZERO information of the system function other than replacing compressors, R134 and oil, basically cleaning and recharging the system.

The basic approach to fixing this AC System is to measuring the temperature into and out of the compressor, and the high/low pressure of the system. The temp out of the compressor will be outside plus 10-20 degrees, and the temp into the compressor should be around 40 degrees. The high/low pressure should be close to 250/30-35

The AC in the 4720 will now put out from 70 to 78 degrees from 80 to 105 degrees outside. IT'S FIXED., but what a pain.

Ted Gage

Generally a system that uses a fixed orifice tube has a pressure sensing compressor clutch cycling switch used to regulate pressure and evaporator temperature.

Usually with a system that uses an expansion valve the compressor remains on and orifice aperture changes to adjust pressure and subsequently regulate evaporator temperature.

Before servicing a system I attach gauges and monitor system pressures against ambient temperature and humidity. More often than not I will charge a system based upon gauge readings and system performance rather than dump and refill. Especially when I have access to a sight glass to monitor liquid line conditions.

If I'm not mistaken another member did have an AC problem at one time and I was surprised to learn that his late model 3 Series cab used an expansion valve and not a fixed orifice tube.

Just checked and here's the expansion valve listed for a 4720 cab. #18 below is definitely not a fixed orifice tube.

View attachment 788943

Hundreds of Millions of CCOT (Cycling Clutch Orifice Tube) Systems used by most auto manufacturers do just that. A low side pressure sensing (cycling) switch turns the compressor on / off to control compressor duty cycle, high side liquid line pressure, low side vapor pressure and subsequent evaporator temperature. And, as you're likely aware, Pressure = Temperature.

Here you go:

View attachment 788969

Further explained here:

View attachment 788977

Over the years I've had the opportunity to support warehouse refrigeration systems and some commercial HVAC and chilling equipment. Maintained and repaired AC and refrigeration equipment on trucks, cars, busses and trailers. Diagnosis started with the basics, using gauges, pressures and a vacuum pump to test system integrity. Beyond engine, motor and / or component replacement system performance was restored solely by charging based upon operating and differential pressures. Sure, a novice can dump and recharge based upon a volume spec but it takes someone who knows what they're doing to make it work "properly" by the numbers.

 

[Kennyd]

Thanks for the follow up Ted!

 

[Weed Free]

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

Remove inter cooler and check to see if condenser is plugged. I didn't have A/C on mine pressures were good would only blow cool air for a few minutes. I always blew out rad but it wouldn't clean condenser.

 

[RodneyLB]

Hi Ted
I'm having similar problems with my 4720 a/c. Thanks for the thorough coverage of your experience. I'm just now starting to trouble shoot mine. My question is, where is the O ring located that you referred to? Also, were you referring to the cabin filter being plugged due to this O ring. I got a little confused at that point. Thanks for the help.

Rodney Brown

 

[ttazzman]

Problem Solved...

This system is NOT a heat pump design. There is a separate evaporator for the heat. And YES, there is an expansion valve hiding on the right side of the evaporator. I ordered and installed a new expansion valve. No difference.

Finally, I went to the John Deere dealer in Weatherford Texas and talked to the AC tech named Troy. We went through the proper settings, charge, and details. As we were finishing up, Troy said he recalled a factory error where they had failed to install an O-ring in the AC System, that the dealers were notified, installed the O-ring, then recharged the AC. However, if the period was too long the filter would start to clog up. Troy remembering this as the last minute was an eureka moment.

Rather than pay John Deere for > $120 for a filter, I purchased one from PitStopAuto for $32. Evacuated the system, removed the old filter, and also tested air flow through the evaporator. The system had to be stopped up somewhere. Now installed the new filter, evacuated the system, charged R134a to 250/30, tested for leaks, and suddenly the return temperature back to the compressor was 40 degrees. WOW.

So, from the beginning, this was a factory manufacturing error. There is no reporting information of this problem. The 900-page System Repair Manual has no AC information except for the proper amount of R134a, oil, etc. There is ZERO information of the system function other than replacing compressors, R134 and oil, basically cleaning and recharging the system.

The basic approach to fixing this AC System is to measuring the temperature into and out of the compressor, and the high/low pressure of the system. The temp out of the compressor will be outside plus 10-20 degrees, and the temp into the compressor should be around 40 degrees. The high/low pressure should be close to 250/30-35

The AC in the 4720 will now put out from 70 to 78 degrees from 80 to 105 degrees outside. IT'S FIXED., but what a pain.

Ted Gage

i am replying to you Ted...so you get notification for the post #27 above ....I was also a bit confusted when i read it

 

[Nate1983]

Did anyone figure out where this O ring is? I’ve got a restriction somewhere in my A/C system on my 3520- new compressor and expansion valve, but still a restriction.

 

[ttazzman]

Did anyone figure out where this O ring is? I’ve got a restriction somewhere in my A/C system on my 3520- new compressor and expansion valve, but still a restriction.

curious as to what caused your diagnosis of a restriction

i am still piddling with mine ...even pulled the cab roof

my 5s will litterally freeze you out of the cab....hard to get better than cool air from the 4s for me

the 4s will keep it tolerable in the cab....i am wondering if i need to change the condenser ...the dealer did a compressor replacement before i took it off the lot i wonder if possibly the condenser has some restrictions in mine i am not sure how to determine if condenser has issues

 

[Superglidesport]

curious as to what caused your diagnosis of a restriction

Same here. Why do you think you have a restriction in your system?

Of course a restricted condenser (8 below) will affect air flow and system performance. Blow it out thoroughly with compressed air then rinse it with a moderate stream of water.

The most common causes of internal restrictions are a ruptured desiccant bag in the receiver-dryer / accumulator (#1 below), the liquid line (#3 below / #10 second graphic) to the expansion valve and the expansion valve (#18 second graphic).

 

[JD Driver]

the 4s will keep it tolerable in the cab....i am wondering if i need to change the condenser ...the dealer did a compressor replacement before i took it off the lot i wonder if possibly the condenser has some restrictions in mine i am not sure how to determine if condenser has issues

A partially plugged condenser will sometimes behave a little like it has a built-in orifice tube. In other words, the condensed refrigerant will be spraying (expanding) at the restriction inside the condenser and causing premature cooling.

It is a bit of a long shot, but if you measure the temperature of the condenser outlet (fitting where line 37 attaches to the condenser) with something like an Infrared thermometer pistol and it is below ambient temperature, then you know that there is partial blockage inside the condenser.

When you put gauges on your system, are you seeing lower-than-normal pressures on the low side which is an indication that there is a flow restriction?

 

[ttazzman]

A partially plugged condenser will sometimes behave a little like it has a built-in orifice tube. In other words, the condensed refrigerant will be spraying (expanding) at the restriction inside the condenser and causing premature cooling.

It is a bit of a long shot, but if you measure the temperature of the condenser outlet (fitting where line 37 attaches to the condenser) with something like an Infrared thermometer pistol and it is below ambient temperature, then you know that there is partial blockage inside the condenser.

makes sense to me......i did go around the system looking for out of the norm hot/cold spots with a infrared thermometer ......will check that closer next time its in my shop ...i am open to all ideas... with the dealer mentioning he put a new compressor on it before i bought it i have to wonder if previous owner did something like put stop leak in it ...or i have no clue how deep the dealer went , knowing it would go out the door soon, i have to assume he did good practices and did the dryer and flushed it out with the compressor but know way of knowing

it is performing ....just underperforming comparitively

thx for the suggestion

 

[ttazzman]

A partially plugged condenser will sometimes behave a little like it has a built-in orifice tube. In other words, the condensed refrigerant will be spraying (expanding) at the restriction inside the condenser and causing premature cooling.

It is a bit of a long shot, but if you measure the temperature of the condenser outlet (fitting where line 37 attaches to the condenser) with something like an Infrared thermometer pistol and it is below ambient temperature, then you know that there is partial blockage inside the condenser.

When you put gauges on your system, are you seeing lower-than-normal pressures on the low side which is an indication that there is a flow restriction?

Tossing some feedback for possible comments

Gages run a bit lower than what I consider normal at 90deg ambient.....I get ~30/200....usually would think 40/200 so it seems in the low side of the range

Temp gunned the condenser inlet temp at 150 and outlet at 95...also seems decent???...

SIGH!!!!

 

[JD Driver]

Tossing some feedback for possible comments

Gages run a bit lower than what I consider normal at 90deg ambient.....I get ~30/200....usually would think 40/200 so it seems in the low side of the range

Temp gunned the condenser inlet temp at 150 and outlet at 95...also seems decent???...

SIGH!!!!

When you shut off the air conditioner, do the low side and high side pressures equalize to the same value within a short period?

I am working on a friends 2006 F150 which also has poor cooling performance. According to the service manual, it uses a low side pressure switch to cycle the compressor clutch, and tries to maintain the low side pressure at an ideal average pressure of 30 psi.

 

[ttazzman]

When you shut off the air conditioner, do the low side and high side pressures equalize to the same value within a short period?

I am working on a friends 2006 F150 which also has poor cooling performance. According to the service manual, it uses a low side pressure switch to cycle the compressor clutch, and tries to maintain the low side pressure at an ideal average pressure of 30 psi.

In past i have never set and observed that balancing to know the duration till it balances .....i tend to pop the gages off and go on......any theorys for next time i put gages on it would be considered

as far as cycling ....i have temp full up and i have not observed it doing any cycling at all ....full on all the time compressor wise ...which leads me to not enough cooling at the evaporator to cause a cycle....i have had the top off to make sure i didnt have air leaks etc accross the evap ...did block off some outside air to force more recirculating air

just temp gunning at vents i see a 10-15deg temp drop from recirculated air .....usually ~70deg at supply air vents

 

[Superglidesport]

Tossing some feedback for possible comments

Gages run a bit lower than what I consider normal at 90deg ambient.....I get ~30/200....usually would think 40/200 so it seems in the low side of the range

Temp gunned the condenser inlet temp at 150 and outlet at 95...also seems decent???...

SIGH!!!!

Considering the ambient temperature at 90˚ the high side is low and under normal circumstances I'd expect the low side to be a bit higher. I wouldn't focus on the low side pressure at the moment. You are checking pressures with the engine running about 1500-1800 RPM......right?? Your pressures are not valid at idle.

I'd say your system charge is low or your expansion valve is stuck open but make sure you're making the correct determination under the right conditions.

TPR chart is below.

 

[ttazzman]

Considering the ambient temperature at 90˚ the high side is low and under normal circumstances I'd expect the low side to be a bit higher. I wouldn't focus on the low side pressure at the moment. You are checking pressures with the engine running about 1500-1800 RPM......right?? Your pressures are not valid at idle.

I'd say your system charge is low or your expansion valve is stuck open but make sure you're making the correct determination under the right conditions.

TPR chart is below.hart is below.

View attachment 854755

Will bring in soon and recheck things.....help me understand why a exp valve sticking open would create a issue....ie not letting system get up to correct pressures?? Does it have a role as a pressure regulator?

 

[Superglidesport]

Will bring in soon and recheck things.....help me understand why a exp valve sticking open would create a issue....ie not letting system get up to correct pressures?? Does it have a role as a pressure regulator?

The expansion valve is either a fixed or variable orifice. Our tractors use a thermostatic expansion valve which regulates the liquid refrigerant entering the evaporator. So yes, a stuck open expansion valve can result in the high side pressure being too low. This is especially the case with a low refrigerant charge.

Another potential issue can be the capillary tube having a dirty or poor connection. It usually mounts in a position where it can sense evaporator temperature and its purpose is to regulate or meter the expansion valve and refrigerant flow.

 

[ttazzman]

The expansion valve is either a fixed or variable orifice. Our tractors use a thermostatic expansion valve which regulates the liquid refrigerant entering the evaporator. So yes, a stuck open expansion valve can result in the high side pressure being too low. This is especially the case with a low refrigerant charge.

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