Question about the necessity of replacing evap core...

[rch10007]

Hi all,

 

I am in the process of a complete teardown of the dash in my '87 Brat and I need to know the truth about evaporator cores.

 

I have always been under the impression that once I "open" the system, you must replace the evap. Is that true? Can I just reuse the old one? Would that be wise considering I have the dash completely apart anyways?

 

I mean, to recharge the system and test for leaks, you vacuum the system before filling it. Wouldn't the vacuum eliminate the humidity, or whatever, in the system before the charge?

 

Am I missing something? The more I think about it, the more it seems ridiculous to replace the evap just because you opened the system. What's the real deal?

 

Thanks!

[DaveT]

 

I have always been under the impression that once I "open" the system, you must replace the evap. Is that true?

 

I don't see why. The evaporator is the heat exchanger under the dashboard. Vacuum for 30-60 minutes should remove any moisture. The thing to replace is the filter / dryer. Small black cylender in the high pressure line from the compressor.

[rch10007]

Thanks Dave. I will check into that!

[nipper]

I think you have it confused with the reciver/drier. That used to be replaced if the system is left open for any length of time. You can proberly get away with reusing it as long as no contaimenets get in it. If the desicant absorbs a lot of humidity, it just means your going to have pull a vacum on the system longer.

 

nipper

[daeron]

If the desicant absorbs a lot of humidity, it just means your going to have pull a vacum on the system longer.

 

nipper

 

 

So the desiccant itself CAN be "dried" in a sense? I wouldve figured once it reached a certain point, it would be saturated and no good..

 

Obviously, I am still trying to learn about car AC systems :-p

[nipper]

http://www.aircoparts.com/1driers.htm

http://www.drivewire.com/replacementparts/acreceiverdrier.html

 

desicant never goes bad, it can always be dried out by heat or by a vaccum. The desicant in a car is of a differnt type, and may break down with time. I dont by thier replace every 3 years things, but do agree about when the system is opened up.

 

nipper

[rch10007]

Thanks nipper! I will definitely get a dryer then! I will also take the cores to a radiator shop for testing before I put the dash back together. I've thought about just replacing them anyway but as soon as I do, I will get the one bad core and end up taking the entire dash apart again!!!

[GeneralDisorder]

On the other hand, my 86's AC system got a bit low and no longer cooled. I replaced all the o-rings at each fitting with new AC rated stuff, and charged it with some old R-12 I had around. Didn't replace anything, and didn't pull any vacuum on it, and it's working fine. If I have to charge it up again with R-134 in a year or a few years so be it - the stuff is cheap. These old AC systems are simple, and frankly the whole receiver/drier setup isn't that big of a deal. Older refrigeration and home AC systems don't even have them.

 

Make sure you have it setup properly to come on with the defrost, and that the idle up solenoid works - this circulates the oil in the system durring the cold season, and prevents hoses, rings and seals from drying out, and the pump from eating itself. It also dries the air for better defrost action.

 

GD

[samneric]

I am about to work on my 256k GMC's AC because the compressor is making very scary sounds.

 

I bought the Haynes techbook to learn about how the system works - useful if you want to get the basic principles. They recommend using AC flush on the Cond & Evap coils definately if a compressor fails (remove metal shards) and as a performance booster to clean sludge and oil build up if desired.

 

I went ahead and bought replacements for all the components due to age/milage. That's a matter of budget though.

 

I hope you bought a recovery system and didn't just let the freon discharge into outer-space

 

Steve

[samneric]

Didn't replace anything, and didn't pull any vacuum on it, and it's working fine.

 

If I understand the system properly, it would work properly whether you pulled a vacuum or not. Pulling the vacuum (evacuating) causes the moisture in the system to evaporate - its a preventative measure that attempts to remove as many foreign substances as possible from the system before recharging with freon.

 

I'm not sure if the dryer would clear out any excess moisture left in there or not.

 

I am neither sure whether even small amounts of moisture going through the compressor would reduce its life expectancy. (We all know you can't compress water right )

 

I'd rather hook up the $10 vacuum pump (Harbour Freight ) to my compressor and let it purge for 10-20 mins just to be on the safe side.

 

Besides, this way, you can also check to see if your repaired system holds a vacuum and therefore doesn't have any leaks....

 

Steve

[idosubaru]

'ive pulled a vaccuum with those harbor freight air compressor tools, works fine the few times i've used them.

[PonchoCatalina]

Another great source for a vacuum pump is Autozone. They loan 'em out for free (as long as you return them - I think the deposit is like $200). They pull a much stronger vacuum than the Harbor Freight venturi pump is capable of, and they don't require that you have an air compressor. The one thing I may caution you about, however, is that every time I've borrowed one from AZ, the thing is virtually empty of oil, and Autozone doesn't sell the stuff. I bought a quart of it at NAPA (ask for vacuum pump oil) for less than $10, and I still have at least half of the container left.

- Ian

[DaveT]

See this thread for a low cost vacuum pump:

 

http://www.ultimatesubaru.org/forum/showthread.php?t=59115&highlight=compressor

 

To be effective, the vacuum has to be strong (hard) enough to boil water at room temperature. An air powered venturi pump won't do this.

 

The receiver / drier could probably be restored by warming it while vacuuming. It would need to be held under those conditions for some time. Not sure how long though.

 

I had one A/C system that ran with air in it, didn't cool as well as it did before, but it did work for a number of years before loosing the freon again.

 

After pulling the vacuum, close the valves, shut of the pump, make sure the system holds the vaccuum for a good while. If it doesn't there is a leak. Cheaper than freon.

[rch10007]

Thanks for help guys!!! I think I will have to try my hand at recharging the system with the gear from Autozone. If not, I know a great mechanic here and I don't mind paying him.

 

I did let the freon out into the air. I didn't think the system had anything in it after sitting in the barn for over 9 years! I was wrong, but it wasn't much. The line hissed for about 2 secs and then the deed was done.

 

Does anyone know where I can get the foam that goes in the core boxes? Is that stuff really necessary. The evap box had a thin liner (padding type) molded to the box. I don't want to reuse - but is it necessary?

 

Can I use regular weather stripping? Will it stand the heat of the heater core. I know that I have to seal off the top and bottom of both cores to make sure the air travels through the cores and not out of the top and bottom reducing efficiency. I tried Napa and Advanced but all they have is weatherstripping. I will check with an AC dealer tomorrow, maybe he'll have the stuff I need.

 

Any ideas about the foam pieces and stripping? Oh, and about the orings?!? Is there a special type I need or size? Are all the orings the same size in the system? They are located where all the hoses connect to something, is that right? Thanks!

[DaveT]

I did let the freon out into the air. I didn't think the system had anything in it after sitting in the barn for over 9 years! I was wrong, but it wasn't much. The line hissed for about 2 secs and then the deed was done.

 

Not enough to worry about. I have always tried to catch the freon, because it is so expensive. So far, no system had a decent charge.

 

Can I use regular weather stripping?

I will check with an AC dealer

 

Weatherstripping would probably work. The A/C guy might have some better stuff. How long do you want / need it to last?

 

and about the orings?!? Is there a special type I need or size? Are all the orings the same size in the system? They are located where all the hoses connect to something, is that right?

 

For freon 12, Buna-N. Not sure about the other stuff, as I don't use it.

Each fitting has an o-ring. The high pressure side uses smaller ones than the low pressure side. A while back, I bought one of the assortments like they have in the store, so I can just match them up. http://www.mscdirect.com. $20- 30.00

 

Be careful when loostening the lines. Use penatrating oil, take time. You don't want to break them.

[rch10007]

I want it to last another 20 years, of course!

 

I've about got the core boxes cleaned up and ready for reassembly but I am stuck until I find the padding I need for the boxes and cores.

 

What do you call that stuff anyways? It's not really weatherstripping or padding. I just don't know what else to call it.

 

Oh well, I'm off to the AC shop and see if they can help. (crossing my fingers)

[rch10007]

I haven't found any of the original type of material to go around the heater core or the evaporator so I did some thinking while wandering around the auto stores.

 

Tell me what you guys think - I know y'all are kings of modification!

 

To go around the heater core:

Get a roll of metal tape and wrap the outside edges of that sucker. Or, I could use gasket material and use some high temp adhesive to stick it to the outside of the core. All this to increase efficiency and ensure the air flows through the core and not out of the top.

 

For the places where the boxes fit together, use regular weather stripping cut to fit.

 

For the doors inside of the boxes, use the same weatherstripping but in some cases, like the blower box - double and triple it up to get the same height as the padding that came off the doors.

 

For the evaporator core box, there was a liner inside. I suppose this was to control moisture and keep the outside of the box from having condensation form. I can take some 1/16 gasket paper and some super tack to make a new liner. Where the pieces join at the edges and could use some silicone.

 

What do you guys think? Sound like it should work ok?

[DaveT]

So you want to fix it once.

 

I *might* be able to get at one of my spare heater systems in a few days... Haven't studied the internals, just never had a reason.

 

The liner is probably insulation to prevent the outside of the box from getting wet with condensation. Maybe cork gasket sheet. http://www.mscdirect.com

 

Weather strip sounds fine for the joints and gaps around the cores.

 

The aluminum tape for ductwork should be good for cold and hot.

 

Look at all the types of weather strip at HD or GOOD hardware store. Look for Frost King X-treme rubber weatherseal.

http://www.frostking.com/windoorweather.php

 

EDPM seems to last a LONG time. I have some outside, exposed to sun part of the day for about 10 years. It only comes in the smaller sizes.

 

For the doors, I would worry about the adhesive un sticking. Mostly hot summer days when parked. RTV might help. Be sure that the surfaces are *clean*. Use something to prevent sticking to the plastic?

[rch10007]

Thanks for the reply Dave!!! I will check out home depot tomorrow. I didn't get there today.

 

And yes, I only want to do this once!

 

I have tons o' time since this is not my daily driver, but I want it to be and so once I am complete, I don't want to have any down time trying to correct a corner that I cut.