AC accumulator

[Bitsyncmaster]

How this info relates to the desiccant in our AC accumulator.

I was under the impression that drawing the vacuum for a few hours would draw the moisture out of the desiccant in the AC accumulator. Well that is not the case. It takes baking in an oven at 220 to 240 deg. F for 24 hours with air circulating over the desiccant to remove its moisture.

I did some testing because I have electronic components that are required to be kept at less than 10 % humidity before they are soldered to my circuit boards. The reason is the component case can absorb humidity and when the component is heated that humidity can create high pressures inside the component and crack the case. If that happens the part works but with age it will fail because the case is not sealed. This requirement is more of a problem when the components are hot air soldered because that heats the whole component to the high temperatures required to melt the solder. When the component is hand soldered, only the leads are heated and the case does not get as much heat.

So I put the old desiccant into a vacuum chamber and left it evacuated at 27 inches (has a gauge on it) and heated it to 100 deg. F for two weeks. I then put that desiccant and a humidity indicator into a sealed glass jar and the indicator (greater than 10% humidity) turned pink in less than one hour.

So you really need to replace the accumulator if your AC has been left open or uncharged for much more than a day. Now how good are the new accumulator seals when they ship them?

[David T]

How this info relates to the desiccant in our AC accumulator.

I was under the impression that drawing the vacuum for a few hours would draw the moisture out of the desiccant in the AC accumulator. Well that is not the case. It takes baking in an oven at 220 to 240 deg. F for 24 hours with air circulating over the desiccant to remove its moisture.

I did some testing because I have electronic components that are required to be kept at less than 10 % humidity before they are soldered to my circuit boards. The reason is the component case can absorb humidity and when the component is heated that humidity can create high pressures inside the component and crack the case. If that happens the part works but with age it will fail because the case is not sealed. This requirement is more of a problem when the components are hot air soldered because that heats the whole component to the high temperatures required to melt the solder. When the component is hand soldered, only the leads are heated and the case does not get as much heat.

So I put the old desiccant into a vacuum chamber and left it evacuated at 27 inches (has a gauge on it) and heated it to 100 deg. F for two weeks. I then put that desiccant and a humidity indicator into a sealed glass jar and the indicator (greater than 10% humidity) turned pink in less than one hour.

So you really need to replace the accumulator if your AC has been left open or uncharged for much more than a day. Now how good are the new accumulator seals when they ship them?

You are correct about replacing the dryer if the system as been at atmospheric for any length of time. For a system that still has *some* refrigerant and pressure the answer is "not always". One way to test is to pull a hard vacuum. 400 Torr and see how quickly it goes up. If the system is tight and the vacuum is lost quickly it is because you are boiling the moisture out of the dessicent. One way to also check is to put a heat lamp on the dryer to raise the temperature. You really can't measure the vacuum properly using a compound gauge. You need to use an electronic one. When in doubt you should just replace the dryer. You should also replace the oil too because it also absorbs moisture and can turn acidic. For a system that has been "dead" for a long time you just replace:
All 3 hoses and seals
Accumulator/dryer
Oil
If necessary the belt and the 2 idler bearings and "O" ring seal
Refrigerant
If the system is contaminated (all black inside) you try to flush it out otherwise you have to replace EVERYTHING (both coils and the compressor).

[Bitsyncmaster]

One way to test is to pull a hard vacuum. 400 Torr and see how quickly it goes up. If the system is tight and the vacuum is lost quickly it is because you are boiling the moisture out of the dessicent.

The point I'm making is you cannot boil the moisture out of the desiccant without using high heat. You would need 240 deg. F at minimum for 24 hours and that would smoke any oil in the used accumulator. If you have other info that says you can do that please show me that info so I can try my vacuum chamber again.

[David T]

The point I'm making is you cannot boil the moisture out of the desiccant without using high heat. You would need 240 deg. F at minimum for 24 hours and that would smoke any oil in the used accumulator. If you have other info that says you can do that please show me that info so I can try my vacuum chamber again.

You use heat along with a hard vacuum. If you see the pressure going up even after using heat and vacuum then you have not gotten all of the moisture out. If you can't get all of the moisture out then you should replace the dryer (along with the desiccant inside). We do it all the time in routine A/C work. BTW, the dryer is considered a disposable item. In larger commercial units you can actually open the dryer up and clean them out and replace the desiccant package. You don't have to get the system 100% dry. Like most mechanical systems they can tolerate small quantities of dirt and moisture but the cleaner it is the longer it lasts. Remember, the desiccant is meant to absorb whatever moisture may be in the system. Over the life of the system it does attract and hold moisture so it is OK for it to have some in it to begin with. The less it starts with the more it can hold.