M7040 - AC works but blows hot after a while

[btcfarmer]

I have a 2014 M7040, and she has around 4500h on her. In reasonable condition over all.

When I bought it, it had an AC leak, which I tracked down to the evaporator under the seat. Big hole in it, I replaced it with a new evaporator and also replaced the expansion valve while I was at it. Replaced the dryer as well. I followed all best practices when recharging system (checking for additional leaks - there were none, flushed system 4 times with pure nitrogen, then recharged with the appropriate amount of refrigerant).

AC now holds the refrigerant fine, there are no leaks. It works so far as that it comes on when I turn it on in cab. Cold air blows, although not as cold as I would wish, usually it only manages around 10-15 degrees Fahrenheit below outside temp. This is when the tractor is idling.

If I work the tractor (~500 RPM) on a warm day (live in Florida, warm day = 80-90 deg F), then the AC will after 30-40 minutes start blowing warm air (warmer than outside even). When this happens, I have observed the AC system pressure to be ~50 PSI low side, ~190 PSI high side.

My understanding is that the AC pressure _should_ be around half that on the low side, and about the same on the high side.

Touching the input and output on the condenser while this is happening, both are quite hot, but the output is less hot than the input.

Questions:
1. Is my low side pressure abnormal, and if so what is likely the cause, given system has a brand new evaporator + expansion valve, and system does work at least while tractor is not too hot?

2. Could it be the condenser being clogged, does my pressure reading support that theory?

3. From my own observation, it seems to me like the condenser receives far too little air flow from the engine fan. Condenser has both the engine radiator and some other type of radiator (not sure what that is for, hydraulic system?) mounted in between it and the engine fan. Just testing with my hand, I feel essentially no draft coming onto the AC condenser while tractor is running. Is this normal?

Thanks in advance for any help!

 

[#40Fan]

You should be able to stick a rag to the front of the condensor and the pull of air through it would hold the rag to it. But, looking at your pressure readings, it wouldn't indicate a high side (air flow) issue unless you were really low on freon.

If you could get a pressure reading when your first start up the tractor, that would help.

Look into that air flow....

 

[DaveFromMi]

Sounds like evap is freezing up. Check the charge level.

 

[lugbolt]

Sounds like evap is freezing up. Check the charge level.

if evap were freezing, it would have to be below about 30 deg F, which isn't going to happen if low side is 50 psi on a warm day.

I'd like to see 30-35 psi on the low side if the cabin air temp is in the 80s, then the low side will start to drop into the 25-30 psi range as the cabin air temp cools.

My "guess" without seeing the tractor in person is that either the compressor isn't up to the task, the belt slipping, or perhaps the expansion valve could be failing. Maybe I'm wrong?

 

[btcfarmer]

You should be able to stick a rag to the front of the condensor and the pull of air through it would hold the rag to it. But, looking at your pressure readings, it wouldn't indicate a high side (air flow) issue unless you were really low on freon.

If you could get a pressure reading when your first start up the tractor, that would help.

Look into that air flow....

Will do the rag test and check on initial pressure asap, thanks!

I am pretty sure the amount of freon is fine, because there are no leaks and I put in the 2.09 lbs (give or take a little ofc) which is what the system is supposed to hold.

As for looking into air-flow, do you mean the air-flow getting sucked in by the blower and pushed out in cabin vents? That pressure is very good. I cleaned that system thoroughly and put brand new filters in both cabin and the cabin roof. Blows strong and consistent from the vents.

 

[btcfarmer]

if evap were freezing, it would have to be below about 30 deg F, which isn't going to happen if low side is 50 psi on a warm day.

I'd like to see 30-35 psi on the low side if the cabin air temp is in the 80s, then the low side will start to drop into the 25-30 psi range as the cabin air temp cools.

My "guess" without seeing the tractor in person is that either the compressor isn't up to the task, the belt slipping, or perhaps the expansion valve could be failing. Maybe I'm wrong?

The belt is fine (recently replaced), and I have manually checked for any slippage - there is none. The expansion valve is also brand new, so I am fairly certain it is fine. I did run the tractor with the seat out so I could inspect the new valve + evap, and saw nothing problematic - no ice buildup or so on either valve or evap.

So would inability to drop the low side pressure to the 25-30 range be indicative of a failing compressor?

 

[Jim L.]

The real diagnostic test to to measure and record high and low pressures; and, temperatures.

However, if it cools for half an hour and them goes warm, the first place to look is air flow (cleanliness). Even if the condenser is clean, if it is not getting sufficient air flow it cannot do the job. That means cleaning the radiator fins, oil coolers, and anything else upwind of the condenser. Evaporator too.

When after 30 minutes and the cool air is going warm, you might try cooling the condenser with cold water while checking the temperature of air coming out of the vents.

But I would think that doing diagnostics before cleaning everything may give inaccurate deductions.

 

[Fedup]

All sorts of "possibles" mentioned, but before changing anything I would pinch off one of the heater hoses and try running like that for a while. See what difference that makes.

 

[Flintknapper]

Did you pull a vacuum on the system before recharging it?

If not....you might have enough moisture in the system to freeze up at the expansion valve (internally). The drier has desiccant but can only handle so much.

There should be a specified amount (weight) of refrigerant the system should hold. Manifold gauges and pressure readings are useful....but when recharging a system that has been evacuated....always 'weigh in' the charge and use the gauges to fine tune the performance.

Typically, when you have sufficient cooling at start up and then it degrades (significantly) you have something freezing up (evaporator, TXV) OR the system is heat soaking (Condenser dirty or lack of air flow).

A low refrigerant charge can cause freezing.

 

[Donystoy]

Just wondering how long the system sat with a "large hole" in the evaporator. If left open for any amount of time it probably got some moisture into the system. When I use to work on these systems you would replace the components like you did and then run a vacuum pump to place the system into a vacuum. Depending on the systems history and size you would determine how long you ran the vacuum pump. Any moisture that had entered the system would then be slowly removed in the vapor discharge of the vacuum pump. I did not see where you indicated that you placed a vacuum pump on the system. Any moisture not removed in the system creates acid which eventually eats holes from the inside out. If this system sat open for a considerable amount of time the compressor could even be corroded internally.
Running nitrogen through the system does nothing with any absorbed moisture that has accumulated in the oil which is everywhere in the system. In fact, in the 34 years that I was in the trade the only time I used nitrogen was when I was brazing copper lines together and did not want any flaking of the copper inside the pipe. To avoid this, you ran a tiny amount of nitrogen through the lines. Nitrogen was also used as a holding charge in new compressors.
Also, you did not mention if you added any oil to the system. When a major leak occurs a lot of oil is carried out along with the refrigerant. One would usually guesstimate on how much was lost and reintroduce the same amount while re-charging.
As far as pressures go, you can probably Google it for that particular refrigerant Ie. 134a. It should give you the pressures at certain ambient outside temperatures etc.

 

[btcfarmer]

The real diagnostic test to to measure and record high and low pressures; and, temperatures.

However, if it cools for half an hour and them goes warm, the first place to look is air flow (cleanliness). Even if the condenser is clean, if it is not getting sufficient air flow it cannot do the job. That means cleaning the radiator fins, oil coolers, and anything else upwind of the condenser. Evaporator too.

When after 30 minutes and the cool air is going warm, you might try cooling the condenser with cold water while checking the temperature of air coming out of the vents.

But I would think that doing diagnostics before cleaning everything may give inaccurate deductions.

10-4 on the need to clean it. I only had a little time to work on it this evening, but used compressed air to blow it out a bit. It had some dust in both radiator, oil cooler and condenser to be sure, but not too crazy. But I may not have gotten it really well, will need to rig up some hoses so I can get in and blow out more areas that are hard to get to.

I ran the tractor this evening and after it got hot, it got warm again. It was 80 outside and it was blowing 81 degree air. I then dumped cold water on the condenser, and the temp started dropping immediately, and was down to about 60 a few minutes later. So a huge difference!

Do you think its still just a matter of dirt?

Air-flow on the condenser is there, but pretty weak. Not enough to hold a rag in place.

 

[btcfarmer]

All sorts of "possibles" mentioned, but before changing anything I would pinch off one of the heater hoses and try running like that for a while. See what difference that makes.

Will try this tomorrow., thanks!

 

[number two]

I think the OP stated he replaced the receiver/drier.

 

[btcfarmer]

Did you pull a vacuum on the system before recharging it?

If not....you might have enough moisture in the system to freeze up at the expansion valve (internally). The drier has desiccant but can only handle so much.

There should be a specified amount (weight) of refrigerant the system should hold. Manifold gauges and pressure readings are useful....but when recharging a system that has been evacuated....always 'weigh in' the charge and use the gauges to fine tune the performance.

Typically, when you have sufficient cooling at start up and then it degrades (significantly) you have something freezing up (evaporator, TXV) OR the system is heat soaking (Condenser dirty or lack of air flow).

A low refrigerant charge can cause freezing.

Yes, I pulled vacuum multiple times, first after putting new pieces in, waited 1h to make sure no leak, then I filled it with nitrogen, pulled vacuum and waited again, and repeated that 4 times before putting the refrigerant in. I was very careful with purging hoses on manifold to not put any air into system. I did weigh the refrigerant and did my best to put in as close to 2.09 lbs as possible (number I've found for this model). Believe I got this part right, but tell me if not.

The thing is the cooling is not sufficient even when I first start the tractor. It does cool the air, but only by about 10 degrees F. So it starts weak and then gets weaker until the air coming out is even warmer than outside temp.

I poured cold water on the condenser today after it started blowing hot air, and this dropped the conditioned temperature from 80 to 60 in a minute. Air-flow seems pretty weak to me, but at the same time I don't think neither condenser, oilcooler or radiator is particularly dirty. Will attempt a thorough cleaning tomorrow.

Thanks!

 

[btcfarmer]

I think the OP stated he replaced the receiver/drier.

Correct. Replaced evap, expansion valve, drier and belt.

 

[Flintknapper]

The belt is fine (recently replaced), and I have manually checked for any slippage - there is none. The expansion valve is also brand new, so I am fairly certain it is fine. I did run the tractor with the seat out so I could inspect the new valve + evap, and saw nothing problematic - no ice buildup or so on either valve or evap.

So would inability to drop the low side pressure to the 25-30 range be indicative of a failing compressor?

You can have 'freezing' INSIDE the expansion valve if the system has moisture in it and the refrigerant charge is too low. That is why two of us have asked if you ran a vacuum pump on the system to boil off the moisture and remove it before recharging the system.

IF your compressor were failing (unable to fully compress) it would manifest as a low pressure reading on both the low and high side. When completely shot (Compressor) pressures will be roughly equal but low on both sides.

Higher than normal readings usually indicate improper refrigerant charge, contaminated refrigerant, dirty condenser/evaporator or insufficient air flow through the condenser.

Is there a fan 'shroud' at the radiator and engine fan? You should be getting a vigorous stream of air being moved across/through the radiator, condenser and any oil coolers mounted. It doesn't sound like this is the case for you. IF you can 'mist' the radiator and condenser and vent temps come down significantly then your refrigerant charge is off and/or you have insufficient air flow.

Remember it is an A/C 'SYSTEM' and all components must be working properly. The pressure shown on the gauges will fluctuate with the ambient (and under-hood) temperatures, so without benefit of those parameters, we can't really say what is going with the charge, except to make general statements.

I would be inclined to check for air flow at this juncture and if nothing is amiss there, I'd evacuate the system and start over (pulling a vacuum and weighing in the charge).

EDIT: I see you responded with new info while I typing the above.

 

[btcfarmer]

Just wondering how long the system sat with a "large hole" in the evaporator. If left open for any amount of time it probably got some moisture into the system. When I use to work on these systems you would replace the components like you did and then run a vacuum pump to place the system into a vacuum. Depending on the systems history and size you would determine how long you ran the vacuum pump. Any moisture that had entered the system would then be slowly removed in the vapor discharge of the vacuum pump. I did not see where you indicated that you placed a vacuum pump on the system. Any moisture not removed in the system creates acid which eventually eats holes from the inside out. If this system sat open for a considerable amount of time the compressor could even be corroded internally.
Running nitrogen through the system does nothing with any absorbed moisture that has accumulated in the oil which is everywhere in the system. In fact, in the 34 years that I was in the trade the only time I used nitrogen was when I was brazing copper lines together and did not want any flaking of the copper inside the pipe. To avoid this, you ran a tiny amount of nitrogen through the lines. Nitrogen was also used as a holding charge in new compressors.
Also, you did not mention if you added any oil to the system. When a major leak occurs a lot of oil is carried out along with the refrigerant. One would usually guesstimate on how much was lost and reintroduce the same amount while re-charging.
As far as pressures go, you can probably Google it for that particular refrigerant Ie. 134a. It should give you the pressures at certain ambient outside temperatures etc.

You are right, I did not think to detail the procedure I followed for recharging it. It had the hole in the evap when I purchased it, so we can probably assume it was like that long enough to where the system had reached 100% equilibrium with the outside.
Here's what I did (after installing new drier, evap and exp valve):

1. Pulled vacuum, left pump on for for almost 2h while doing this.
2. Turned pump off and closed system down to observe if it would hold negative pressure, waited 1h plus - no change.
3. Filled with nitrogen, and pulled vacuum again, times 4 (I was advised to do this by someone who works with ACs, but I admit I did not look up exactly what this would achieve, I just did it because it sounded like a good idea lol)
4. Finally recharged with the refrigerant, and I also put in a little dye and some PAG oil, which was mostly guesstimated yes. Refrigerant is R134a. 2.09 lbs (I weighed it, and tried to get as close to 2.09 lbs as possible as per tractors stated capacity).

It is definitely possible the compressor is corroded on the inside. In hindsight I wish I would have replaced it as well.

Today I ran it hot and then poured some cold water on the condenser. This had the effect of dropping the output temp from 80 to 60 in just 2-3 minutes. I don't know if this means the compressor is fine, or if it might still be the culprit (or one of the culprits).

Thanks!

 

[Flintknapper]

Yes, I pulled vacuum multiple times, first after putting new pieces in, waited 1h to make sure no leak, then I filled it with nitrogen, pulled vacuum and waited again, and repeated that 4 times before putting the refrigerant in. I was very careful with purging hoses on manifold to not put any air into system. I did weigh the refrigerant and did my best to put in as close to 2.09 lbs as possible (number I've found for this model). Believe I got this part right, but tell me if not.

The thing is the cooling is not sufficient even when I first start the tractor. It does cool the air, but only by about 10 degrees F. So it starts weak and then gets weaker until the air coming out is even warmer than outside temp.

I poured cold water on the condenser today after it started blowing hot air, and this dropped the conditioned temperature from 80 to 60 in a minute. Air-flow seems pretty weak to me, but at the same time I don't think neither condenser, oilcooler or radiator is particularly dirty. Will attempt a thorough cleaning tomorrow.

Thanks!

The A/C system on a tractor because of lack of insulation and lots of solar gain (from all the glass) will not usually perform as well as on a vehicle. Still you should see vent temps 25-30°F less than the ambient temp outside if things are working tip-top.

It sounds to me that you have an air flow problem at the very least.

 

[DustyRusty]

I was going to make a suggestion, however, all the things that I thought of have already been mentioned. When I do AC work I pull a vacuum for a minimum of 24 hours, and then charge with nitrogen and note the pressures. If it holds the nitrogen for another 24 hours I will charge the system weighing the refrigerant as I install it. Most times I will put 80% of the stated refrigerant into the system, and then run the system watch the gauges, and slowly add refrigerant on the low side until I get the gauge readings that are shown in the service manuals. The only thing I can think of that hasn't been mentioned is whether you wrapped the expansion valve with the black refrigerant cork tape, properly affix the sensing bulb to the evaporator core, and wrapped it with the black refrigerant cork tape. I only work on old car systems using R-12, and that stuff is so expensive that you don't want to make mistakes.

Update: I just read one of your replies, and realized that you only guessed at the proper amount of refrigerant oil. If I were doing that repair, I would have pulled the compressor and drained the oil, flushed the system with a refrigerant flushing agent, and blown it out with compressed nitrogen to make sure that the system was clean of any debris. Working on refrigeration is like a surgeon doing surgery, you have to have a clean environment and clean piping. If the system was open to the atmosphere, you have no idea of what might have gotten into it.

 

[btcfarmer]

You can have 'freezing' INSIDE the expansion valve if the system has moisture in it and the refrigerant charge is too low. That is why two of us have asked if you ran a vacuum pump on the system to boil off the moisture and remove it before recharging the system.

Yes sir, I did pull a vacuum on it before recharging. First let the vacuum pump pull for almost 2h, and then waited with the system closed but gauges still connected, to ensure no leak. Then I flushed with nitrogen multiple times, each time pulling vacuum again (have since learned this may not have been a useful thing to do).

IF your compressor were failing (unable to fully compress) it would manifest as a low pressure reading on both the low and high side.

Great insight for me, thank you. Whatever my problem is, it sounds like it's not the compressor failing at least.

Higher than normal readings usually indicate improper refrigerant charge, contaminated refrigerant, dirty condenser/evaporator or insufficient air flow through the condenser.

Is there a fan 'shroud' at the radiator and engine fan? You should be getting a vigorous stream of air being moved across/through the radiator, condenser and any oil coolers mounted. It doesn't sound like this is the case for you. IF you can 'mist' the radiator and condenser and vent temps come down significantly then your refrigerant charge is off and/or you have insufficient air flow.

Yes, there is a shroud like that. It was never really dirty, had some dust and debris on it. I cleaned it somewhat today, will do a better job tomorrow with more time. But I would certainly not describe the airflow hitting the condenser as vigorous. It seems weak to me, and it is not enough to keep a rag in place.

Remember it is an A/C 'SYSTEM' and all components must be working properly. The pressure shown on the gauges will fluctuate with the ambient (and under-hood) temperatures, so without benefit of those parameters, we can't really say what is going with the charge, except to make general statements.

I will give it a more thorough cleaning, reassess and come back with more detailed data.

I would be inclined to check for air flow at this juncture and if nothing is amiss there, I'd evacuate the system and start over (pulling a vacuum and weighing in the charge).

EDIT: I see you responded with new info while I typing the above.

Will start by cleaning it more thoroughly tomorrow and see if I can improve air-flow. My charge may not be perfect, but I can say for certain air-flow is very poor right now, so that seems like the best place to start.

Thanks for your help!