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AC pressure readings and problem with dealer.

1693TA

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Joined
Feb 27, 2010
Messages
2,687
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Farmington IL
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FAA Radar Engineer, (Retired)
I mentioned subcooling in post #25. That is the way to do it for a TXV system, if the condenser is big enough to actually subcool. If it's inadequate, you can end up dumping more and more refrigerant until the high side gets too high and the compressor is overworked. But high side does not seem too high on this system, so
I mentioned subcooling in post #25. That is the way to do it for a TXV system, if the condenser is big enough to actually subcool. If it's inadequate, you can end up dumping more and more refrigerant until the high side gets too high and the compressor is overworked. But high side does not seem too high on this system, so my guess is that it needs more, but that is only a guess.

You did mention subcooling and I negated the input as you did not include anything else. We know subcooling and superheat play hand in hand and an undersized, or inefficient coil, (condenser) will drive compressor discharge pressure up, increasing workload on the driving motive, with negative effects on superheat. Too little superheat, (flooding of the evaporator coil) or too much superheat, (evaporator starving or undercharged system, or lack of adequate airflow across the coil) equate to the same result; customer complaint(s). Condenser subcooling sets up the inlet path for superheating to take place in a closed loop system such as mechanical refrigeration.

I'm not going to add a lot to confuse or lose track of the OP's concerns, but I feel he is victim of another "Franchised Box Swapping Ape Show" because what has been posted so far indicates the servicing "technicians" are lost in the problem. He should find another dealer since this is a warranty scenario. OEM customer service will sometimes authorize this very easily.

We all do things different to achieve the same favorable result. Hopefully this scenario plays out well and all will be good.
 

Doug580l

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Apr 15, 2018
Messages
301
Location
Southern Illinois
OP here again. I appreciate everyone's help. I am planning to try talking to the service dept. again and probably the salesman. It took me about 10 minutes of arguing with him to get the service guy to agree to even look at it the second time, so I assume this time won't be any better. I do like the idea of them authorizing it to be serviced at another Bobcat dealer. I will bring that up. I think they are blowing me off because I am not a contractor with a bunch of machines, could be wrong.

When they looked at it the second time they said there was a clogged drain line and they fixed it and everything is fine. I used the machine for a few hours the other day and after about a half hour or so I noticed a little water coming out of a couple of the vents. I looked at the drain tubes and 1 of them was missing the rubber drain valve at the end of the tube. I assume it's sucking in air from there and it's getting into the vents now. Also, with the machine running there is none, or very little water coming out of the drains. As soon as I turn the ac off, a lot of water comes out of the drains.
 

Birken Vogt

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Nov 30, 2003
Messages
5,354
Location
Grass Valley, Ca
If the evap is icing up, then cooling will be poor, and refrigerant flow will be low leading to low pressures on the system. Might be on to something there. There should be a switch that disengages the compressor clutch on low evap temp or low suction side pressure or something like that. One way to prove this scenario is to run the blower on high all the time and engage the AC only some of the time in order to keep the water thawed out. If the controls will let you do that.

If you switch off the cooling and keep the blower on high and a whole lot of melt water runs out, so much more proof to the problem.
 

1693TA

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Messages
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Farmington IL
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FAA Radar Engineer, (Retired)
OP here again. I appreciate everyone's help. I am planning to try talking to the service dept. again and probably the salesman. It took me about 10 minutes of arguing with him to get the service guy to agree to even look at it the second time, so I assume this time won't be any better. I do like the idea of them authorizing it to be serviced at another Bobcat dealer. I will bring that up. I think they are blowing me off because I am not a contractor with a bunch of machines, could be wrong.

When they looked at it the second time they said there was a clogged drain line and they fixed it and everything is fine. I used the machine for a few hours the other day and after about a half hour or so I noticed a little water coming out of a couple of the vents. I looked at the drain tubes and 1 of them was missing the rubber drain valve at the end of the tube. I assume it's sucking in air from there and it's getting into the vents now. Also, with the machine running there is none, or very little water coming out of the drains. As soon as I turn the ac off, a lot of water comes out of the drains.

Chances are the water droplets coming out of the vents are being blown off the evaporator coil by the blower motor because the airbox is not draining the condensate water out. If you have condensate water, the evaporator is not freezing, (usually). You mentioned these drain tubes were clogged. This can be for a couple of reasons but I don't know your system or design so can only go with educated guesses. If you have a selection of recirculated air, or outside air, (as automobiles do) using outside air will quickly plug or foul filters and the airbox drains as this type equipment doesn't typically reside in the a clean environment. If this case use recirculating air only. If there is a filter in the system, it will be prior to the blower motor. Ensure this is clean and stays that way. Either no filter, or a clogged filter will eventually dump what it cannot hold into the airbox and this could clog your drains. Those rubber "Vacuator" tips on the airbox drains do a good job of letting the water out and disallowing dust and dirt in when they are new. As they age they tend to not perform quite as well. This should be no affect on your machine citing age yet.

Another scenario I've seen a couple of times in the automotive world is the foam strips that separate the heater core from the evaporator core section(s) either misplaced during assembly, or rotting apart from age clogging the drains. This can also allow heated air which is blown through the airbox to escape over into the evaporator compartment warming your discharge air. Not so much of an issue with the heater operation as you don't run the heater and air conditioner at the same time during the colder months.

As far as condensate water escaping faster from the drains when the system is shut down is usually a pressurization problem in the ducting meaning restricted airflow through them. The water is probably "pooling" someplace and when the blower motor is not running the path to drain is less restrictive. That is just a guess however. The root problem here is usually dirt or something fouling the discharge path. Compressed air blown back through the drains will temporarily remove a clog and sometimes clear it, but a short burst of air only as you don't need to blow anything up.....
 

Old Doug

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If it's a warranty issue and the dealer doesn't have techs. experienced enough to fix it, they should be the ones paying to have it taken somewhere that knows what they're doing. No way the owner of a new machine with only 100 hours should have to pay $100/hr.+ to fix what should be a warranty issue.
Your exactly right but thats not the way things work alot of the time. I would be in jail if i bought something new and couldnt get them to fix it. If they didnt want to fix this i would get a sheet of ply wood and paint a sign telling what was going on and park the machine as close to the dealer as i could. The way a warranty works from what i have learned is the customer has a problem the item if cheap gets replaced or money refunded . If is a big item they try to repair it if that dosent work they try to stall till the warranty runs out. My brother bought a used car it wasnt very old and had a warranty before the warranty was up he started hearing a noise he keep taking it back warranty runs out trans gos out . Turns out this car was known for trans problems what do you think was going on the dealer had to know these cars had a trans problem and the noise was something to do with that.
 

Welder Dave

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You bought a new machine for 10's of thousands of dollars. The AC doesn't work. The dealer fixes it or authorizes someone else to fix. If the dealer won't do that you contact Bobcat directly. Reference to a used car is apples and oranges. If your brother could prove they knew about the trans. problems, he could sue them for gross negligence. In your case it's a brand new machine and everybody is fully aware of the problem. They can't stall till the warranty runs out. You could say it's too unbearable to work in and ask for another machine or your money back. The dealer and/or the OEM need to to fix it for you. You shouldn't have to get forceful but sometimes they force you to. What if the engine was the problem and the dealer couldn't fix it? It doesn't matter if you're a 1 machine operation. They need to fix it for you, that's why you have a warranty in the 1st place. Take them to task!
 

Doug580l

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Apr 15, 2018
Messages
301
Location
Southern Illinois
If the evap is icing up, then cooling will be poor, and refrigerant flow will be low leading to low pressures on the system. Might be on to something there. There should be a switch that disengages the compressor clutch on low evap temp or low suction side pressure or something like that. One way to prove this scenario is to run the blower on high all the time and engage the AC only some of the time in order to keep the water thawed out. If the controls will let you do that.

If you switch off the cooling and keep the blower on high and a whole lot of melt water runs out, so much more proof to the problem.
Good idea! Didn't occur to me to try that.
So after running the machine until there was some water coming out of a vent, about 30-40 minutes I left the fan on high and turned off the ac. No extra water coming from the drains. At that time there was a slow drip out of the drain that still had the rubber valve on the end and nothing on the one they removed the valve from. As soon as I turned off the blower there was a lot of water coming out of the drains, especially the one they removed the valve from. Did the same test with the blower with the ac on and same results.

Also, I kept track of the temps at the vents at different time periods. It was about 86 degrees and humidity was quite a bit lower than usual. Blower was on the highest setting. After running about 10 minutes the temp was about 47 degrees. That's the lowest I can remember seeing it. 20 minutes later the temp was about 60. 6 minutes later it was 64. 5 minutes later it was 55 and I first noticed some water coming out. After that I let the machine site at full throttle- in eco mode and watched the temps. They would fluctuate between 56 and 62 degrees. I have no idea what any of this means. Hoping somebody does.
 

Doug580l

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Messages
301
Location
Southern Illinois
You bought a new machine for 10's of thousands of dollars. The AC doesn't work. The dealer fixes it or authorizes someone else to fix. If the dealer won't do that you contact Bobcat directly. Reference to a used car is apples and oranges. If your brother could prove they knew about the trans. problems, he could sue them for gross negligence. In your case it's a brand new machine and everybody is fully aware of the problem. They can't stall till the warranty runs out. You could say it's too unbearable to work in and ask for another machine or your money back. The dealer and/or the OEM need to to fix it for you. You shouldn't have to get forceful but sometimes they force you to. What if the engine was the problem and the dealer couldn't fix it? It doesn't matter if you're a 1 machine operation. They need to fix it for you, that's why you have a warranty in the 1st place. Take them to task!
You're absolutely right. I've been trying to be nice about the whole thing but that's getting me nowhere. I will give them 1 more opportunity to fix it before I go to Bobcat. Although the dealer claims there isn't a problem, lol. I think I'll talk with the salesman first before I talk to the service guy. The salesman is very aware that the main reason I bought the machine form them was because of concerns about service. I would of bought a Yanmar, which was considerably cheaper but the dealership was a small farm equipment dealer that has only been selling the Yanmars for 2 years. When I asked the Yanmar salesman about their mechanics training or experience working on them he wouldn't give me a straight answer.
 

fastline

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Here is all the data for my 322. 100F ambient, still pulling down. One snapshot at idle, another at WFO. TXV on these does run low pressures. Verified in the books because I didn't like it. However, she pulls on down to 'ball freeze' levels after a bit.

I do work on HVAC obviously. Will help where I can here. If your ambient is 95F+, on a cold start (cab is hot as hell), you better be seeing head pressures over 200. I do agree with one poster is the charge removed SHOULD BE WEIGHED OUT! That is highly important to determine what is in it. That tells a huge story right there!

You have 100hrs on the machine. I would not suspect a plugged anything! It is possible the compressor is ****. Pulling all the data like I have provided starts to paint the real picture of performance!

Not trying to step on toes, but there is some pretty inaccurate advice in this thread!

The issue with SH/SC in mobile systems is the huge variables of compressor speed and condenser airflow! It is valuable info, but these are moving targets! I know what I am looking for. I will be honest, my system could use a few more oz.... but I am rolling it. F it!
 

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Old Doug

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You bought a new machine for 10's of thousands of dollars. The AC doesn't work. The dealer fixes it or authorizes someone else to fix. If the dealer won't do that you contact Bobcat directly. Reference to a used car is apples and oranges. If your brother could prove they knew about the trans. problems, he could sue them for gross negligence. In your case it's a brand new machine and everybody is fully aware of the problem. They can't stall till the warranty runs out. You could say it's too unbearable to work in and ask for another machine or your money back. The dealer and/or the OEM need to to fix it for you. You shouldn't have to get forceful but sometimes they force you to. What if the engine was the problem and the dealer couldn't fix it? It doesn't matter if you're a 1 machine operation. They need to fix it for you, that's why you have a warranty in the 1st place. Take them to task!
In both of these deals if every one has proof that they have a problem and tryed to get it fixed then at the end of the day they could get a lawyer and try to sue but i dont know what he gave for the car it could have easly been worth alot if it was only a year old. But going to court the good guy dosent always come out the winner. I have been there before and court isnt always about write and wrong its who is lucky and has a good lawyer.
I have made alot of mistakes in my life and its easy to point out when others make mistakes my brother made a mistake and Doug5801 has to they should have never left the lot until they thought the problem was fixed.
 

partsandservice

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Feb 14, 2011
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847
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Georgia
To hell with trying to get them to fix it. The amount of down time , I would just put the new thermostat switch in it and move on. I thing this thread has let you know what is wrong with it. The ac cools till the core freezes. Then will work agaiin briefly after it melts. If you could see the evaporator corre when it quits cooling it would look like a block of ice , not just frost. The thermostat typically has a capillary tube that stick in the fins of the evaporator. It cuts the compressure off to keep the core from freezing.
 

fastline

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I will assume the machine is at the dealer at this point. What they need to do is contact Bobcat and triple verify the charge amount for the system. I know they are going to look it up and weigh in exactly that much. That is the extent of their experience! All indications I see so far is either a bad compressor, or possibly just low charge. In cases where head pressure is low and suction is normal-ish, it would be prudent to add refrigerant to see if head pressure climbs. These systems are sensitive to charge so it should not take much to affect some change.

What should be checked is the subcool on the liquid line, which will further confirm there is a big problem. That unit will run with an H valve TXV and liquid receiver/dryer. We check the subcool to ensure we are getting nothing but liquid to the TXV. If there is little or no subcooling, we know there is gas going to the TXV, and that will not work.

We run higher head pressures in mobile to 'force' subcooling. Since the vaporization temperature is relative to the temp, and the temps run quite hot, we have to run head pressures up to ensure we have liquid to the TXV.

For a few reasons, I am doubting the icing theory. If head pressure is low, subcool will be low, so capacity is not even there to ice up. as well, the system will run a temp sensor at the evap as well as a suction line pressure sensor, both working to ensure it does not ice up. I am sure Bobcat (if they understood anything) could plug in and simply review the temp sensor value. That value would be largely helpful. Remember that these systems are designed to cycle on and off and it is part of the design to run evap temps down near freezing before cycling the compressor. If the temp sensor was bad, I would think a code would be present as the system will also be looking at other values and determine its state.

The other possible scenario is a faulty TXV that is overfeeding. I am doubting that because if it was bad enough to drop head pressure that much, suction side would likely be higher.

Oh, I should mention that I am going off the low head pressure for guidance. That aside, the first thing I would do is find the fresh air cabin filter bay and plug it with a plastic sheet. I have seen this before where people are chasing their tail with AC temps, they are in recirc mode, but guess what? That damper no worky! You won't get cold air without recirc.
 
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suladas

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I think before I dove too deep into it, I would be checking vent temps of other machines that are new or newly new to make sure that's just not how they are. While it may not seem good enough, if that's how they are made your issue isn't with the dealer at all.
 

Birken Vogt

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Grass Valley, Ca
I agree after hearing about the water dripping/blowing while it's running, it may not be icing. Usually when it's icing, it will just continue to freeze until shut off. I did have a KW one time that would work fine most of the time and suddenly decide to ice up completely, and then half an hour later finally cut off the compressor leading to fogging the windshield and a lake of water. Usually that happened in winter, though. We never did figure that one out nor could the KW dealer.
 

Doug580l

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Apr 15, 2018
Messages
301
Location
Southern Illinois
I will assume the machine is at the dealer at this point. What they need to do is contact Bobcat and triple verify the charge amount for the system. I know they are going to look it up and weigh in exactly that much. That is the extent of their experience! All indications I see so far is either a bad compressor, or possibly just low charge. In cases where head pressure is low and suction is normal-ish, it would be prudent to add refrigerant to see if head pressure climbs. These systems are sensitive to charge so it should not take much to affect some change.

What should be checked is the subcool on the liquid line, which will further confirm there is a big problem. That unit will run with an H valve TXV and liquid receiver/dryer. We check the subcool to ensure we are getting nothing but liquid to the TXV. If there is little or no subcooling, we know there is gas going to the TXV, and that will not work.

We run higher head pressures in mobile to 'force' subcooling. Since the vaporization temperature is relative to the temp, and the temps run quite hot, we have to run head pressures up to ensure we have liquid to the TXV.

For a few reasons, I am doubting the icing theory. If head pressure is low, subcool will be low, so capacity is not even there to ice up. as well, the system will run a temp sensor at the evap as well as a suction line pressure sensor, both working to ensure it does not ice up. I am sure Bobcat (if they understood anything) could plug in and simply review the temp sensor value. That value would be largely helpful. Remember that these systems are designed to cycle on and off and it is part of the design to run evap temps down near freezing before cycling the compressor. If the temp sensor was bad, I would think a code would be present as the system will also be looking at other values and determine its state.

The other possible scenario is a faulty TXV that is overfeeding. I am doubting that because if it was bad enough to drop head pressure that much, suction side would likely be higher.

Oh, I should mention that I am going off the low head pressure for guidance. That aside, the first thing I would do is find the fresh air cabin filter bay and plug it with a plastic sheet. I have seen this before where people are chasing their tail with AC temps, they are in recirc mode, but guess what? That damper no worky! You won't get cold air without recirc.

Before the machine was brought in the first time, I added about 8oz. of refrigerant to it. It made no change to the pressure readings.
 
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