Regenerating A/C Dryer Desiccant

[Ian H.]

September 15th, 2003, 11:58 AM
Jack Humphrey (17100)

Default Correct....
plastic plugs to prevent atmosphere for entering and no special 'seals'. The active ingredient in receiver dryer isn't rocket science, fellas. It's simply silica (remember the old salt shaker lids that absorbed moisture, changed color and you baked the moisture out in the oven?).

The original receiver dryers were meant to be serviced. The sight glass was removable. You could pop it off, dump the contents, replace with off-the-shelf fresh silica (in sealed packets available through GM service), and completely rebuild the jar. In fact, that's what those offering 'restored original' receiver dryers do using scrap yard donors.

Heck, you can do yours yourself at home! Take it off, fill with isopropyl alchol, swish, and dump. Repeat as necessary until the effulent comes out clear & clean. Now, plug the holes and mask the sight glass. Media blast the exterior and lay down a fresh coat of paint. Pop the sight glass and lay in fresh rubber refigerant gaskets for the next 25-years. When all is done, put the finished receiver dryer in your kitchen oven on 'keep warm' setting overnight to force absorbed moisture out of the silica pellets inside and PLUG the inlet/outlet holes when you take 'er out of the oven to cool. You're done!

Found the above quote in the Archives.

I'm wondering if I should try this on my '67, since the dryer hasn't been used for very many hours, but my system has been depressured for about a month, with only plastic plugs inserted at the compressor fittings. Compressor is out for a seal and bearing change.

At oil refineries, driers are regenerated (or dried) by circulating heated air or nitrogen through them until the moisture content meets specs. So it makes sense to me.

But back to the Corvette's dryer.
- If you use isopropyl alcohol, would you use one with a high percent as shown on the label?
- If you dry it out in an oven, do you remove the sight glass and rubber seal first?
- Would a temperature of 250 degrees F. for 16 hours be OK?

[Kirk M.]

[Jack H.]

Re: Regenerating A/C Dryer Desiccant

"At oil refineries, driers are regenerated (or dried) by circulating heated air or nitrogen through them until the moisture content meets specs. So it makes sense to me."

Nitrogen as an air bath to dry is GREAT! The phone company also uses this approach to dry out underground cables that've been water-logged. But, few individuals have access to bulk N2...

"But back to the Corvette's dryer.
- If you use isopropyl alcohol, would you use one with a high percent as shown on the label?
- If you dry it out in an oven, do you remove the sight glass and rubber seal first?
- Would a temperature of 250 degrees F. for 16 hours be OK?"

(1) The last time I restored a dryer for my car, I used off-the-shelf rubbing alcohol from WalMart and simply ran it through in multiple passes until the effulent I dumped came out clean/clear.

(2) GM used to sell a receiver/dryer rebuild kit that provided the correct amount of fresh silica. I don't know if that item is still available. But, if it is, removing the sight glass and rubber gasket is the best way to get all the old silica out of the receiver dryer.

(3) I didn't remove/replace my sight glass + gasket and it withstood the oven bake nicely.

(4) Exact oven temp? Well, you want to be at/near 212F to 'cook' existing moisture out and anything above that temp is probably overkill...

(5) If one goes to this extent to rejuvenate a factory original receiver/dryer, I guess I'd say why not go and remove the sight glass, clean it up and install a fresh gasket too? Decent refrigeration grade gaskets are only pennies... BUT, there's some chance you'll 'fight' getting the existing sight glass out + you could 'crack' it in the R&R process. So, it's a matter of personal preference and I left my original alone....

[Ian H.]

Re: Regenerating A/C Dryer Desiccant

I assume by your description, you are then going to replace with fresh silica and reseal. Correct?

No. Since it doesn't have a lot of hours of usage, I don't plan on changing the silica.

Kirk and Jack; Thanks for your input

[Wayne M.]

Re: Regenerating A/C Dryer Desiccant

Jack H; others --- I bought this NOS Receiver / Drier back in early '80s from the local GM dealer, for my C2. Never used it, and now, when I tilt it to one end then the other, I hear a soft thump, as if the silica has formed a plug which is sliding to the low end. Does this mean that those screwed in fittings (which I've never removed) have allowed moisture to enter ?

Second question; is the silica (being inert in itself) compatible with both R12 and R134a ?

[Joe R.]

Re: Regenerating A/C Dryer Desiccant

Hi Wayne:

It is my understanding that a different dessicant is required for R134a, but at least one of the available versions is backward compatible with R12.

[Joe R.]

Re: Regenerating A/C Dryer Desiccant

Hi Jack:

I had the impression that the dessicant was held in some sort of cloth or fiber bag. One thing that would concern me about changing the dessicant in an old drier would be the possibility that the bag itself has deteriorated. I gather that one of the known failure modes for an AC system is for the bag to break, allowing dessicant to travel throughout the system and generally clog things up.

In your earlier post you said that the rebuilders simply change the dessicant, but that is not what Classic Auto Air told me they were going to do when I sent them my original drier for a rebuild. They said they would cut the drier open on a lathe, install a new dessicant bag with dessicant, and re-weld the housing back together.

I can not independently verify that they actually did this, but I have no reason to doubt them.