Why does Tesla recommend replacing the A/C dessicant bag as a maintenance item?

[zroger73]

I was very surprised to learn that Tesla recommends replacing the "A/C dessicant bag" every 2-6 years (depending on year and model) as a maintenance item.

I understand the purpose of dessicant in a refrigeration system, but once the dessicant absorbs any moisture that may remain in the system after the initial charge, it should have no further function since no additional moisture can get in unless the system loses its charge due to a leak or is opened for repairs.

So, why is this recommended in a Tesla, but no other refrigeration system that I've ever seen or heard of?

 

[MobileClimate]

All Oems recommend changing the drier every 3 years …there is a filter in there and it’s important for it too remove compressor contaminants so they don’t plug up expansion valves and allow Poe oil to flow thru the system to return back to the compressor clean . The desiccant inside does break down over time.

 

[zroger73]

All Oems recommend changing the drier every 3 years …there is a filter in there and it’s important for it too remove compressor contaminants so they don’t plug up expansion valves and allow Poe oil to flow thru the system to return back to the compressor clean . The desiccant inside does break down over time.

I've worked on mobile A/C systems in ICE-powered automobiles since the 1970s and I have never replaced or heard of replacing desiccant as a maintenance item. Tesla is the first automaker I've seen to specify doing so.

Can you point me to any other manufacturer's instructions that specify replacing desiccant as a maintenance item? I'd like to see this from the manufacturer.

 

[240vPlug]

I am not an HVAC pro and have limited knowledge of these systems. However I will say that this is a heat pump system and with the supermanifold I would think the system might be a little more sensitive to any contamination. What is the cost of the maintenance vs the cost of replacing a contaminated system?

 

[MobileClimate]

There just making sure the system doesn’t have any moisture in it ..unlike the drive motor which doesn’t reach over 170F and doesn’t need an oil change or filter change the discharge temperature does get high on the AC pump on hot days up to 240F and higher and it if it has moisture in it it will create an acid and Poe oil breaks down ….but if it was me I wouldn’t change the drier on this scroll unit because the design of it is very simple and it doesn’t have pistons or a front compressor seal that breaks down with excessive heat .so .no I wouldn’t change the filter on a sealed factory system that doesn’t have a leak. Hopefully tesla evacuated the system to 100 microns at the factory on every car with all the valves open so no air is trapped ..I would hope tesla did that on every car don’t know of they do

 

[zroger73]

I am not an HVAC pro and have limited knowledge of these systems. However I will say that this is a heat pump system and with the supermanifold I would think the system might be a little more sensitive to any contamination. What is the cost of the maintenance vs the cost of replacing a contaminated system?

"Regular" air conditioning systems are heat pumps, too. The refrigerant cycle is the same - whether the system is heating or cooling, low pressure gas refrigerant enters the compressor and high pressure gas refrigerant exits the compressor. The only difference is that a heat pump has a reversing valve that exchanges the roles of the evaporator and condenser. A Tesla has a reversing valve for this purpose just like a heat pump for a building. What makes a Tesla's thermal management system different is the Octovalve, but that switches the flow of coolant, not refrigerant. The desiccant is in the refrigerant system - not the coolant system.

 

[MobileClimate]

And having no front compressor seal makes that compressor better than any ice vehicle period ..the comp seals leak all the time on ice vehicles especially after they get over heated..I wouldn’t have the money to purchase a model x if it wasn’t for the high failure rate of compressor seals on systems with a low charge

 

[stopcrazypp]

I was very surprised to learn that Tesla recommends replacing the "A/C dessicant bag" every 2-6 years (depending on year and model) as a maintenance item.

I understand the purpose of dessicant in a refrigeration system, but once the dessicant absorbs any moisture that may remain in the system after the initial charge, it should have no further function since no additional moisture can get in unless the system loses its charge due to a leak or is opened for repairs.

So, why is this recommended in a Tesla, but no other refrigeration system that I've ever seen or heard of?

From a quick search the C8 Corvette also recommends replacing the desiccant every 7 years:
AC Desiccant replacement - MidEngineCorvetteForum.com
As does a bunch of other GM models:
https://ownersmanuals2.com/chevrolet/malibu-2021-owners-manual-78161/page-308
https://ownersmanuals2.com/gmc/sierra-1500-2022-owners-manual-83988/page-418
https://my.gm.ca/content/dam/gmowne...evar25=ch_bolt-recall_owners-manuals_bolt-euv

The 2014 Volt had a 10 year recommendation for a full flush and desiccant replacement:
https://www.dezosmanuals.com/wp-content/uploads/2021/09/2014-Chevrolet-Volt-OM.pdf

The VW ID.4 also has a 7 year interval for desiccant change:
https://www.vwoaklawn.com/service/service-parts-information/do-electric-cars-use-oil/

There are articles suggesting they may break down eventually if not replaced:
How Long Does an AC Receiver Dryer Last? | YourMechanic Advice

 

[MobileClimate]

Those cars dont have 5 electronic expansion valves like the tesla heat pump system so your not comparing apples to apples

 

[stopcrazypp]

Those cars dont have 5 electronic expansion valves like the tesla heat pump system so your not comparing apples to apples

I'm not comparing or making any comment on how long is appropriate, just giving some examples of desiccant replacement intervals in other brands, since OP asked for them.

 

[240vPlug]

Some good reading on supermanifold. Can it hurt to perform the maintenance? Seems like a failure would be more expensive. An ounce of prevention perhaps?

Tesla Octovalve analysis - E-Mobility Engineering

The engineering details at the heart of the model Y's heat pump, as provided by an independent stripdown

www.emobility-engineering.com

 

[Unclepaul]

It is not unusual for Tesla to be conservative with new systems. Later they may extend the service intervals as they learn more about it robustness.

They used to recommend a routine differential oil change every few years. Now they have the statistics to make it more of an extended service needs.

 

[zroger73]

Those cars dont have 5 electronic expansion valves like the tesla heat pump system so your not comparing apples to apples

There are 2 expansion valves in the patent diagram - the same number that's in many heat pumps (lower-end heat pumps use one expansion valve for cooling mode and one fixed orifice for heating mode).

Perhaps you're confusing the 5 positions of the Octovalve? Again, only coolant - not refrigerant - flows through the Octovalve, so desiccant isn't involved there.

 

[MobileClimate]

Yes you are correct there is 2 but this system is working with temperatures of the refrigerant at really low temps so moisture could freeze at the expansion valve. Other ac systems dont work at that low temperature ..this is more like a refrigeration system not an ac system . One more note that if the expansion valve had moisture freeze up the valve it would cause the scroll compressor to go in a vacuum which would be extremely bad because its using the refrigerant as the lubricant for the compressor ..but i'm sure tesla has a pressure switch to avoid that

 

[STS-134]

From a quick search the C8 Corvette also recommends replacing the desiccant every 7 years:
AC Desiccant replacement - MidEngineCorvetteForum.com
As does a bunch of other GM models:
https://ownersmanuals2.com/chevrolet/malibu-2021-owners-manual-78161/page-308
https://ownersmanuals2.com/gmc/sierra-1500-2022-owners-manual-83988/page-418
https://my.gm.ca/content/dam/gmowne...evar25=ch_bolt-recall_owners-manuals_bolt-euv

The 2014 Volt had a 10 year recommendation for a full flush and desiccant replacement:
https://www.dezosmanuals.com/wp-content/uploads/2021/09/2014-Chevrolet-Volt-OM.pdf

The VW ID.4 also has a 7 year interval for desiccant change:
https://www.vwoaklawn.com/service/service-parts-information/do-electric-cars-use-oil/

There are articles suggesting they may break down eventually if not replaced:
How Long Does an AC Receiver Dryer Last? | YourMechanic Advice

The claims in that last article don't seem right. There is literally NO way for new moisture to get into the system. It's a closed system, and it's under fairly high pressure. If there is a leak, the refrigerant will leak out, but nothing from the atmosphere will get in until the pressure equalizes, and by that point, you'll have lost so much refrigerant that the system won't work. If they're talking about oils for compressor lubrication breaking down or debris from the compressor clogging the dryer, that's different, but moisture? That's not going to happen. And the only one that really makes sense to me is oils breaking down because if you're getting debris (like metal shavings, etc.) from the compressor going into the refrigerant, your system is very close to failure already.

 

[stopcrazypp]

The claims in that last article don't seem right. There is literally NO way for new moisture to get into the system. It's a closed system, and it's under fairly high pressure. If there is a leak, the refrigerant will leak out, but nothing from the atmosphere will get in until the pressure equalizes, and by that point, you'll have lost so much refrigerant that the system won't work. If they're talking about oils for compressor lubrication breaking down or debris from the compressor clogging the dryer, that's different, but moisture? That's not going to happen. And the only one that really makes sense to me is oils breaking down because if you're getting debris (like metal shavings, etc.) from the compressor going into the refrigerant, your system is very close to failure already.

I think the article is implying the desiccant may eventually break down and then clog the rest of the system. Don't know how valid it is, just posted it given it came out during the search. The more important point is there are other manufacturers that have similar intervals, so Tesla is not alone.

 

[STS-134]

I think the article is implying the desiccant may eventually break down and then clog the rest of the system. Don't know how valid it is, just posted it given it came out during the search. The more important point is there are other manufacturers that have similar intervals, so Tesla is not alone.

But they basically say that the reason it eventually needs replacement is that it absorbs too much moisture: "The receiver dryer contains desiccant pellets that absorb moisture. Once they have absorbed a great deal of moisture, they will no longer serve their purpose, and the receiver dryer will need to be replaced."

That doesn't make sense, because all of the moisture they absorb should go in at the very beginning. Chemical changes that occur over time as a result of having absorbed moisture at the very beginning? Well...not really, because there's this:
"Unless you use the air conditioner in your vehicle a great deal, the receiver dryer will last a long time – about three years. At that point, the desiccant pellets will have deteriorated to the point that they will actually break down, clog up the expansion valve, and possibly even damage the compressor."

Maybe chemical changes that occur as a result of the refrigerant being hot and moving through the desiccant? In any case, what they're actually saying makes no sense. It may well be the case that something happens as a result of using the system that causes the desiccant to break down and need to be replaced, but their explanation of why it happens doesn't make sense.

 

[MobileClimate]

If a tech was to replace that drier he would have to remove the refrigerant and i can almost guarantee he would put the refrigerant in a contaminated recovery tank and would get air in the system somehow..SO you would have a new drier that would remove moisture that he just put into the system but then your performance would be low because of the air that got caught in the system because he didn't follow the procedure to open all valves during evacuation ..remember this system only holds just a little more than 2 lbs of refrigerant

 

[MobileClimate]

I was wrong 6 exp valves not 5

Electronic Expansion Valveslink​

In an expansion valve, refrigerant drops in pressure and temperature when expanding and transitions from 100% liquid into vapor/liquid mixture (coexistence). The supermanifold has 6 expansion valves on it, described in the sections below.

 

[STS-134]

I was wrong 6 exp valves not 5

Electronic Expansion Valveslink​

In an expansion valve, refrigerant drops in pressure and temperature when expanding and transitions from 100% liquid into vapor/liquid mixture (coexistence). The supermanifold has 6 expansion valves on it, described in the sections below.

View attachment 916872

EXV LCC? And expansion valve that goes to the LCC? So the LCC can act as a chiller?