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Low side had frost on it. Help

concretefire on Fri June 03, 2011 12:39 AM User is offline

Year: 1995
Make: Dodge
Model: Dakota
Engine Size: V-6
Refrigerant Type: R-134a
Ambient Temp: 90
Pressure Low: ?
Pressure High: ?
Country of Origin: United States

So, here's the deal. I need help. My local auto shop wants $90.00 just to evac the system, inspect the system, and recharge the system. Now...that's not too bad. I understand that. But I KNOW they are going to find a problem, and then charge me out the ying yang for the repair when I feel very confident I can fix it myself......at least to the point where I can then take it to the auto shop and let them do their thing and charge it properly.

I have done all sorts of repairs on my truck myself. Changed water pump. Changed intake manifold gasket, even took the bed off my truck myself and got to the fuel tank and fixed the sending unit to the dash because the dash always said I was empty on gas. My point is, I can figure things out and fix things as long as I know where to look first. That's why I am here.

You can rip me all you want (I can take it), but I decided to at least "try" one of the autozone R-134a refill cans. It came with a guage. I had the A/C on full blast, and set on the coldest level. I had driven 15 miles to the store, so the engine was at operating temp. The directions said to set the dial to the outside ambient temp which was close to 90 degrees. I did that. I then hooked it up to the low side and started to charge it slowly. The guage got real close to being at the "correct" level for the outside temp and I didn't want to over fill it. When I say real close, I mean within 5-10 psi. It was close.

The can was empty. I jumped back in the truck (it was running by the way) and right away, I was getting cold air. What a relief!!!! It wasn't super super cold, but it was at least MUCH BETTER than what it was. I knew if I had a leak in the system, in a few days, it would be blowing luke warm air again. Sure enough, about 3 days later, it went from cold to not cold at all.

Returning from a trip I left the truck running. I popped the hood. I was going to hook the guage up to the low side to get the reading of pressure...and to my shock, the WHOLE LOW SIDE LINE had white frost on it. All the way from the front of the radiator all the way back to the firewall.

By the way, I did hook up the guage just for kicks and it read maybe 5 psi, I mean it was pathetic. Here's the kicker.....*IF* I have a leak, I have read that it leaves an oily residue on the hoses somewhere, usually at the joints. My hoses look brand new and I can't find ANY "residue" anywhere. Not from the compressor, following every line, as far as it will go, there is no oily residue or tell tale signs of leaks. It looks clean. I even took a white towel and ran it all the way along the hoses especially at the joints and came away with very little dirt, but it wasn't oily at all.

1) What would make the low side "frost" like that.....after only 3 days of what I considered to be "decent" cooling after the refill from autozone?
2) Obviously, I have a leak somewhere...correct? Or could it be something else?
3) When I refilled it with R-134a from autozone, I WAS SATISFIED for a day or two.

I don't mind spending the $90 to get it properly recharged and what not, but I do not feel comfortable spending that kind of money only for them to tell me I have a problem. DUH!!! I KNOW I have a problem. I'm trying to find it and fix it myself BEFORE I let them recharge it correctly. ANY HELP Would be appreciated. Thank you.

mk378 on Fri June 03, 2011 1:04 AM User is offline

It could be overcooling and icing up due to a bad pressure switch or electrical problem. (An iced evaporator will make the vents go warm because there is no airflow possible through the ice). You should get accurate readings with real gauges first. Compressor should not be engaged at 5 psi.

Edited: Fri June 03, 2011 at 1:05 AM by mk378

concretefire on Fri June 03, 2011 1:37 AM User is offline

I found a free A/C systems check from AAMCO with a coupon. I'll bite the bullet and go there, turn in my coupon, get it checked out and tell them DO NOT FIX ANYTHING....just tell me what's wrong. Can't hurt right?

tomw on Sat June 04, 2011 12:24 PM User is offlineView users profile

There is a LPCO switch that should have de-energized the compressor when the pressure in the evaporator fell below twenty-something. It is supposed to prevent the evaporator from freezing into a block of ice and preventing air flow, just as mk378 said.
You stated it went from cooling to not cooling, but not clearly.

Was it cool when you started out, and slowly got warmer as you drove, and then when you checked the line was frosted? If so, your compressor is working as is your condenser and evaporator. But. The LPCO is not, and you are likely low on refrigerant. If AAMCO tests it, they should find a leak. They should not offer to replace any parts until they can justify that it indeed doesn't work with no leaks and a MEASURED proper charge. They should note the LPCO failure, IMO, and it would make sense to check or replace that.
tom

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