Help me decide on the AC system

[Eddie H.]

Originally Posted by davepl

I'm up against a few walls here: oil in the compressor, never flushed the lines, I think I got all of the o-rings but can't be sure, and the compressor is an old original (actually a 'new' rebuilt original from LMC, but how good that is I don't know).

Since I'm using all era-correct hardware, I think I'll stick era-correct R12. Especially the leak thing worries me (smaller molecules?)

But what is this "RED TEK" stuff that claims to be "both":

Amazon.com: RED TEK 12a Refrigerant 20 Lb Cylinder (60 Lb Equiv): Automotive

I'd buy a cylinder of R12 and haul it in with me, as $272 doesn't seem bad, but I can't even tell if it's real R12, so likely just leave it up to the HVAC guy to source it.

I think I would stay away from the Red TEK stuff as well, since Genuine R12 is still readily available. The last R12 AC system I rebuilt was on a 71 GMC. It had been open and inoperative with parts missing for 20 years. I just flushed out the evaporater and condenser, replaced the hoses and drier, put on a Delco reman A6 compressor, leak tested and charged with R12, and it has been operating perfectly for a year now.

[Davidf]

I should add that after I had the OE A6 compressor rebuilt (my a/c system was still intact when I purchased the truck and a slight amount of pressure when I opened it up), it held a vacuum (30") for hours. The compressor was leak free for a few weeks before it started slinging oil on the inner fender, fender, and hood. Yep, my halogen leak detector confirmed the shaft seal was leaking.

[Eddie H.]

Yep, it's rare to find someone who can rebuild a compressor properly. I have had pretty good luck with AC Delco reman parts, but a lot of the others are just pure junk.

[hdff]

How much r12 goes in a new system, fixing to put mine together and need to get some

[davepl]

I'd like to know also, since he's going to charge me for the fill obviously. You can buy "20lb tank, 60lb equivalent" on Amazon, as linked above, but I'd call that 20lbs.

What I don't know is do our systems take 10, 50, or 100lbs of it?

[Waldoe]

If it were 134a, mine held 2lbs 9oz. R-12 below. This is taken from a 1969 service manual

[leddzepp]

3.25 lbs of R-12 and 10 oz oil for a factory system.

[davepl]

That's CRAZY if it can really pull 120F air down to 48F. My house sure can't do that...

[Waldoe]

thats outside 120 air at condenser, not inside air.

[davepl]

Originally Posted by Waldoe

thats outside 120 air at condenser, not inside air.

Which is even more challenging because the house is usually in "recirc" mode where it's dropping ambient room temp. If the truck AC can take outside 120F air and chill it to 48F, I think that's pretty impressive.

Combine the tiny cab with a rocking, high-flow AC system and it must cool down very quickly on a hot day.

[Andy4639]

I did a couple of mods on my 71 and it will run at 40* weather moving are stopped.
First was I closed off the cowl vent outside of the passenger side completely. I sealed it up with metal. Then I placed black foam around the radiator to force the air through the condenser and radiator + I added the panels between the grille and support.
Something a lot of people over look also is the heater core water shut off valve. I put a manual one in the line opposite of the vacuum valve to keep hot water from entering the cab at all. This is good for a few * when it's 90-100 outside.

[davepl]

Why not let the cowl flap and heater valve work as they're supposed to? Mine doesn't leak much air (I used a new flap) if any, and there's a heater valve from the factory, so it sounds like you did what's already there???

Move the lever away from Recirc, the cowl seals. The heater valve is closed in any AC mode.

[Davidf]

Originally Posted by davepl

Which is even more challenging because the house is usually in "recirc" mode where it's dropping ambient room temp. If the truck AC can take outside 120F air and chill it to 48F, I think that's pretty impressive.

Combine the tiny cab with a rocking, high-flow AC system and it must cool down very quickly on a hot day.

I don't think that chart is saying what is inferred above. 120 degrees at the condenser is NOT the same as taking 120 degree air at the evaporator and chilling it to 48 degrees...doubt it will do that.

Also, you cannot compare automotive systems to home systems. Best your going to get from you home system is typically a 20 degree differential between return and supply air. The system is designed for electrical efficiency and it does not need to rapidly bring the temperature down like a auto a/c needs to...

[davepl]

If the condenser is in front of the radiator, isn't the temp of the air entering the condenser the same as the outside air temp? At least while moving?

I was as surprised as you at how I'm reading it, but I'm not sure how else to read it.

[Davidf]

Yes, but you are not cooling the air at the condenser, you are cooling the air at the evaporator. Which, will be much lower given test criteria...whatever that might be.

Still, this shows the how efficient R12 is at shedding latent heat. Need a much larger condenser to get the same numbers with R134a, if at all.

[hdff]

Originally Posted by leddzepp

3.25 lbs of R-12 and 10 oz oil for a factory system.

thanks for the info.... aren't most cans 12ozs so 3.25 would be 4 1/2 cans give or take?

[leddzepp]

Originally Posted by hdff

thanks for the info.... aren't most cans 12ozs so 3.25 would be 4 1/2 cans give or take?

Some are 12 oz, I think I've seen 16?, not sure. I picked up five of these 14 oz cans at a swap meet last summer. I'm going to use it in my 68 when I rebuild the factory AC next spring.