AC too cold?

[davepl]

Hard to say because we had to run it indoors (it's like 40F out) to check the AC. After filling, the top tube on the evaporator under the hood (the tube that goes into the core) frosts up and turns white, so it's darn cold. But is that a symptom of too cold? Discharge air was 38F or something very chilly.

I just don't know a lot about AC and wonder if there's not an adjustment that's supposed to be made to prevent icing. If it's icing on the exterior, I worry about inside the housing.

[cleszkie]

I don't believe that it should be icing on the exterior. Do you have the correct pressure differential between the high and low pressure sides? Correct pounds of refrigerant? What was the ambient temperature of the garage you were testing it in?

[davepl]

Ambient was probably 65-70. I was not present to read the manifold gauges but the guy that filled it presumably knew what he was doing (famous last words).

I'm told he only added about 2.7lbs while the reproduction label on the compressor indicates 4lbs. What made him stop at that lower number I don't know.

I know low refrigerant can cause icing, I wonder if maybe he saw too much pressure diff and stopped adding refrigerant for some reason?

The AC tech is a stop-by service, my shop isn't EPA certified, so I have to ask the shop that brought him in second hand. He was, however, well recommended by people I trust, for what that's worth.

[cleszkie]

Just for clatification, is is your system a stock Harrison set up? Has it been modified to use 134A or do you still use R12? Was the reproduction label intended to indicate pounds of R12? If so, and if you are using 134A, then the poundage of required 134A that the tech installed may be correct.

[davepl]

Originally Posted by cleszkie

Just for clarification, is is your system a stock Harrison set up? Has it been modified to use 134A or do you still use R12? Was the reproduction label intended to indicate pounds of R12? If so, and if you are using 134A, then the poundage of required 134A that the tech installed may be correct.

It's a stock Harrison setup; it had the 134 fittings on it when I got the truck, but I used all new components from the expansion valve forward, more or less (compressor, dryer, hard lines, etc).

We were indeed filling it with 134A but made no modifications other than new parts and whatever was done when whoever in a previous life installed the 134A fittings.

Thanks for the 134vs12 and poundage, that makes me feel a little better!

[FirstOwner69]

From a previous thread it sounded like you were going with R12. So, my response is based on that.

Below are 2 pictures of compressors that may help answer your question about how much R12 refrigerant should be in the system. The 1st pic showing 3.75# is of my original 1969 compressor. However, when new, it had a sticker added showing 3.25# as seen in the 2nd pic. I peeled the label in the 2nd pic off a 69 or 70 truck in the junkyard. My original hoses were shorter than those on the later trucks which were the same as the reproductions. The extra hose length may account for later systems requiring 3.75#.

EDIT: Given everything I said, I just checked the 70 and 72 service manuals. Both say capacity is 3 lbs. 4 oz. AND now I see that, while I was typing, you stated you went with 134A.

[1972RedNeck]

Originally Posted by cleszkie

I don't believe that it should be icing on the exterior.

Mine did. Blew ice cold but never seemed to ice up on the inside enough to block air flow.

[FirstOwner69]

Originally Posted by 1972RedNeck

Mine did. Blew ice cold but never seemed to ice up on the inside enough to block air flow.

Same here.

[leddzepp]

Originally Posted by FirstOwner69

Same here.

X3, and still does (using R-12)

[motorcritter]

The frost on the hose isn't a big concern, unless you've got really cold port temps- which you don't. Thirty-eight degrees F is right about where you want it. Much colder and you can freeze the evaporator, and that is not good.
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[Andy4639]

If he did this sitting inside a shop did he have any kind of fan blowing air through the radiator while servicing it. If not that could be why it was icing up.