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Dash A/C Compressor Failure


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I'm just wrapping up replacement of the dash air conditioning compressor in our 2005 Exec with the Series 60. I was on a short exercise run and was checking to see if the dash system was cooling -- the incorrect way, by putting it on MAX AC and seeing if it go cold. Note to self: that's what gauges are for. The compressor froze up and shredded the serpentine belt. Fortunately, ours only uses one belt, so the only loss was charging from the alternator but it runs OK with the generator on charging the chassis bank through the Big Boy (another story on corrosion inside that).

My question is: aren't these systems supposed to self-protect and refuse to engage the clutch if pressure is too low? Does anyone know how to test this function short of destroying another compressor and belt by running it without refrigerant?

I don't recall seeing a lot of posts on this issue over the years, although I did have the exact same issue back in 2012. Coincidence that I'm losing the compressor roughly every 8 years? I generally never thought of replacing the A/C compressor as a PM item.

For info and the Parts List, the original Sanden U4420 compressor was replaced with a Four Seasons 68158. The drier was Global Parts 1411487. About $250 total in parts to replace. Invested maybe another $60 for a flush tank and fluid.

Key reminder: even though I always try to take a picture(s) when replacing parts, when the belt shreds it's tough to tell how it was routed. I wasted a couple of days (and a few Amazon returns) fussing with the wrong size belt before I got a picture of a similar setup (thanks, Paul Busch!) and magically the original sized belt was perfect.

 

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repeat compressor failures is usually associated with not flushing the system out thoroughly after the last failure.  Or not replacing the dryer.  Second cause is lack of lubrication.  If the system has been leaking and the freon keeps getting topped up to keep it running without adding the proper oil, then the oil leaves with the freon and makes the compressor run dry.  Or crappy parts.

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This post raises a very important question because I have added freon to my systen 3-4 times in past 14 yearsnever more thana pound or less to complete charge.Could someone please share a particular brand of oil that has been successfully used and how to install to system? I would rather add some oil than new system! 

 Thank's,

Bruce Crocker 

2004 Diplomat 40' PDQ 

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You are right about the low pressure switch,  it should be there and the clutch lead should go through it.  Ours is right at the drier up front. You can test it since your systems is or will be evacuated. Once you locate the switch, you might also remove it without losing any pressure and test it that way, should be open with no pressure to it. You might also have a high pressure switch,  I don't.

I used PAG 100 oil, I think, but it's been a while  since then and I don't see the viscosity being that critical. There should be a mention in your manual? In a pressurized system you would need an Injector or a pressurized can and alway fill the low pressure side very slowly.

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First let me say that I’m no AC expert, but picked up a bit of information on compressor failure from several sources, and the information is the same.

I have a 2005 Windsor, side radiator with a Danfoss controller.  It seems they were programmed to not turn on at low rpms (such as idle), unless the engine temp calls for fan.  My Ac cooling is mounted with the radiator.  Some were mounted up front and had a fan to cool.

So, many times while stopped and idling, the AC is not getting proper cooling and that is a killer for compressors.  Some people simple turn the AC off when idling or add a supplement cooling fans which runs anytime the AC is on.

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14 hours ago, SkyKingII said:

This post raises a very important question because I have added freon to my systen 3-4 times in past 14 yearsnever more thana pound or less to complete charge.Could someone please share a particular brand of oil that has been successfully used and how to install to system? I would rather add some oil than new system! 

 Thank's,

Bruce Crocker 

2004 Diplomat 40' PDQ 

Not good to add oil unless you are replacing a part.  Excess oil accumulates in the condenser reducing efficiency.

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1 hour ago, David White said:

First let me say that I’m no AC expert, but picked up a bit of information on compressor failure from several sources, and the information is the same.

I have a 2005 Windsor, side radiator with a Danfoss controller.  It seems they were programmed to not turn on at low rpms (such as idle), unless the engine temp calls for fan.  My Ac cooling is mounted with the radiator.  Some were mounted up front and had a fan to cool.

So, many times while stopped and idling, the AC is not getting proper cooling and that is a killer for compressors.  Some people simple turn the AC off when idling or add a supplement cooling fans which runs anytime the AC is on.

Good point David.   It was a known problem and there is a modification.   I think it was Chuck B that talked about having the modification done.   IIRCC it was simply    drilling a small hole to allow enough fluid to continue flow so the fan would to operate at idle.     Maybe Chuck will see this and share more info about doing the mod.

Bruce,  There are 2 types of oil out there for air cond, the right one must be used for the refrigerant in a system which will be R134 in yours.   I'm pretty sure it will state    this on the cans.  The question I have is how much?   My guess is not much.   How much is not much?    I don't know but maybe someone can help.

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19 hours ago, DavidL said:

repeat compressor failures is usually associated with not flushing the system out thoroughly after the last failure.  Or not replacing the dryer.  Second cause is lack of lubrication.  If the system has been leaking and the freon keeps getting topped up to keep it running without adding the proper oil, then the oil leaves with the freon and makes the compressor run dry.  Or crappy parts.

David A/L,

Thanks for the quick response. I did not do the work after the first failure in 2012, so I don't know if they flushed the system or just evacuated (guessing the latter). I realize that it's coincidental that I've experienced another failure roughly 8 years later, so it could be that some contamination circulated for 8 years before getting trapped in the compressor.

I do know that the receiver/drier was replaced in 2012, and I replaced it again now. Since 2012, I'd say that maybe 2 12-ounce cans of R-134A were added. I don't know enough about dilution to know if that would have necessitated adding lubricant but will research.

The original compressor was a Sanden (based on the Build Sheet) and the 2012 replacement was a Four Seasons. Do you know if either brand qualifies as "crappy"?

Thanks,

19 hours ago, SkyKingII said:

This post raises a very important question because I have added freon to my systen 3-4 times in past 14 yearsnever more thana pound or less to complete charge.Could someone please share a particular brand of oil that has been successfully used and how to install to system? I would rather add some oil than new system! 

 Thank's,

Bruce Crocker 

2004 Diplomat 40' PDQ 

Bruce,

It's called "PAG Oil" and comes in 46 and 100 weight viscosity. I found a "Supercool" brand 8-ounce bottle of PAG 46 on Amazon and added 4 ounces directly to the compressor using the port on top of the housing.A tag on the housing said it was pre-charged with 3 ounces and oil needed to be added, but not how much.  I will say that the manufacturer's documentation for the compressor was completely silent on general quantities needed; everything was make/model-specific and "Monaco" wasn't listed. I have no idea if I have too much or too little. A "x ounces per y pounds of R-134A" guideline  or something similar would have been very helpful.

I also found a video on Youtube showing how to add oil via one of the Schrader ports, but I had the new compressor on the bench prior to installation so didn't need to go that route (and I don't have a vacuum pump).

Hopefully, someone with more experience can clarify.

Thanks,

18 hours ago, Ivan K said:

You are right about the low pressure switch,  it should be there and the clutch lead should go through it.  Ours is right at the drier up front. You can test it since your systems is or will be evacuated. Once you locate the switch, you might also remove it without losing any pressure and test it that way, should be open with no pressure to it. You might also have a high pressure switch,  I don't.

I used PAG 100 oil, I think, but it's been a while  since then and I don't see the viscosity being that critical. There should be a mention in your manual? In a pressurized system you would need an Injector or a pressurized can and alway fill the low pressure side very slowly.

Ivan K,

I plan to do some diagnostic work on the pressure switch before having the system evacuated and charged. I'll also research how much oil should really be used.

Thanks,

7 hours ago, David White said:

First let me say that I’m no AC expert, but picked up a bit of information on compressor failure from several sources, and the information is the same.

I have a 2005 Windsor, side radiator with a Danfoss controller.  It seems they were programmed to not turn on at low rpms (such as idle), unless the engine temp calls for fan.  My Ac cooling is mounted with the radiator.  Some were mounted up front and had a fan to cool.

So, many times while stopped and idling, the AC is not getting proper cooling and that is a killer for compressors.  Some people simple turn the AC off when idling or add a supplement cooling fans which runs anytime the AC is on.

David W,

I've seen those posts over the years but my system has the A/C condenser mounted just behind the front axle. I will definitely try to see if there is a different issue with mine that could cause the same failures, though.

Thanks,

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Since your compressor fried, I would take it apart to see what fried.  If it's on the freon side of the compressor, then you HAVE to take the whole system apart to flush / reverse flush / dry each component.  Most important is the condenser.  All of the hoses.  Count on doing this.  Takes a half a day.  I start at the modulating valve to see if there is any dirt / desiccant clogging the ports which indicates the whole system needs a good cleaning.

 

Before opening the system, check to see if there is any dirt around fittings.  Good sign that's where the freon  / oil went.  Once you do that, I power wash the whole system, especially the condenser.  Use degreaser if needed.  And yes, use care with the power washer not to hurt the fins.  Always better to work on a clean AC system so dirt is less possible to enter.

Sometimes people shortchange flushing the evaporator because it's very hard to get any flush solvent out of it.  I put a white rag on the output side to check for any dirt coming out of the component.  Ideally flush dry the components with clean nitrogen.  Lots of people use shop air that has a paint spray moisture remover in line with the hose.  Ensure the compressor tank is dry.  Shoot the shop air into the air to rid the hoses of moisture and then apply the air to the AC component to be dried.

The modulating valve, the dryer and the gaskets all need to be replaced post flushing.  And certainly the compressor / clutch.

You can look up how much and type of oil charge.  The new compressor will tell you the type.  Subtract the amount of oil that the compressor comes with.  If you don't know for sure, dump it out into a graduated cylinder and measure how much.  Put the required amount into the compressor.

Put the whole system back together and put a 2 stage vacuum pump on it for HOURS.  Shut the pump off and ensure no vacuum drop over the next hour.  If any drop, you have a leak somewhere that needs to be fixed before putting freon in the system.

Once it's all pumped down, start the  motor, put the AC on MAX, put the specified qty of freon back into the system, looking at the gauges the whole time to ensure no overpressurizing.

If you really want to get crazy, dump the freon out using a recycle center, take the compressor out and again measure how much oil is now in it (post running).  Add if it's below spec (how much the compressor ships with).  ReVac and recharge.  Document how much freon, the type and quantity of oil added to the system for the next time.

Edited by DavidL
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George, that is good with the the front AC condenser location.  If I remember correctly (again with no first hand knowledge), it has an auxiliary fan there too. Is that working?

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I second the recommendation to take the compressor apart. If it overheated due to lost charge or lack of oil, the center ball would probably be welded to the gear. Sanden has a public service manual to help diagnose common failure modes. Knowing what I know now, I'd measure the amount of oil in the old compressor, and also cut open the old receiver/dryer and see how much crud is in it.

https://www.sanden.com/objects/Failure_Analysis_Web.pdf

image.png.a7016f529ec900a316155de90251d1af.png

The binary switch which servess to turn the compressor off on high head and lockout the compressor on lost charge, in my experience, isn't that reliable. I evacuated my system and it still took some time for the switch to open (reasonably new switch). Especially since there's no sensor on the low side, if the charge is lost while the compressor is running, the system won't shut down until the high side goes <28 psig by which point everything would be pretty well cooked. Was there still a charge in the system when you went to replace?

Looking at the factory oil charge on the 4420, it comes with 6.75oz. My 4475 came with 10 oz and I still ended up adding 4 oz to it to get the crankcase level right (long suction lines tend to pool oil and these guys come filled for semi tractors). I wonder on the original replacement how much oil was installed. PAG 100 is the right stuff (Sanden calls it SP-15).

Edit: the Sanden procedure for measuring oil was updated to run the compressor at a given RPM and then make sure a given quantity of oil was in the system by taking it off and draining it into a container. Mine is not easy to install, so I used the legacy dipstick. I flushed ours with 2 gal of naptha and it took about 2 hrs with a single stage vacuum pump to reach a stable vacuum (700 microns). Replaced the condenser out of paranoia, but when I cut the old one open, it looked just fine.

Edited by trailmug
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23 hours ago, trailmug said:

I second the recommendation to take the compressor apart. If it overheated due to lost charge or lack of oil, the center ball would probably be welded to the gear. Sanden has a public service manual to help diagnose common failure modes. Knowing what I know now, I'd measure the amount of oil in the old compressor, and also cut open the old receiver/dryer and see how much crud is in it.

https://www.sanden.com/objects/Failure_Analysis_Web.pdf

image.png.a7016f529ec900a316155de90251d1af.png

The binary switch which servess to turn the compressor off on high head and lockout the compressor on lost charge, in my experience, isn't that reliable. I evacuated my system and it still took some time for the switch to open (reasonably new switch). Especially since there's no sensor on the low side, if the charge is lost while the compressor is running, the system won't shut down until the high side goes <28 psig by which point everything would be pretty well cooked. Was there still a charge in the system when you went to replace?

Looking at the factory oil charge on the 4420, it comes with 6.75oz. My 4475 came with 10 oz and I still ended up adding 4 oz to it to get the crankcase level right (long suction lines tend to pool oil and these guys come filled for semi tractors). I wonder on the original replacement how much oil was installed. PAG 100 is the right stuff (Sanden calls it SP-15).

Edit: the Sanden procedure for measuring oil was updated to run the compressor at a given RPM and then make sure a given quantity of oil was in the system by taking it off and draining it into a container. Mine is not easy to install, so I used the legacy dipstick. I flushed ours with 2 gal of naptha and it took about 2 hrs with a single stage vacuum pump to reach a stable vacuum (700 microns). Replaced the condenser out of paranoia, but when I cut the old one open, it looked just fine.

I like that Sanden compressor diagnostics article.  Good stuff.  Sucks when one sees that on your own RV, but at least one then knows what happened.

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