C4ProjectCar

Sorry to keep inundating you guys with incessant posts asking for help. This car just has lots of problems.
My AC wasn't working and had no freon pressure at all, so I decided to evacuate it and refill with R-134a. I cleaned out the lines, replaced the seals and Schrader valves, and evacuated the system. When I refilled it, I shorted the low pressure plug to cycle the compressor as instructed in the FSM. A few minutes in, the plug stopped sparking when I shorted it and the compressor clutch stopped engaging. Now the compressor won't engage so I can't finish filling it with freon.

Other applicable information:

• 1990 C4
• C68 Automatic Climate Control
• The light to indicate fan setting (recirculate, top and bottom, just top, just bottom, etc.) now blinks instead of staying solid. I found that this means there is an error code - the code mine had was low freon. I'm going to disconnect the battery to clear the code and see if it comes back.

C4ProjectCar

Okay, I figured it out. Not sure why this worked, but it did. After I disconnected and reconnected the battery, I started it and the compressor kicked on. Yay!
I hope this helps someone else.

DUB

Have you checked the fuse???

Now...that you have a 'blinking light' that it telling you that you have a problem and you can find it by looking in the service manual to manually pull up the trouble code. This usually has to be corrected.

Also...you MAY need to remove a battery cable to reset the system.

Remember to compensate the amount of Freon you put into the system...because you car had R12 originally...and you DO NOT put the same amount in. As I have been told by my A/C guy....80% of what would have NORMALLY been used should go in. For whatever that is worth to you.

DUB

cudamax

First you don't short anything. You most likely just took out a A/C Fuse. Pull the low pressure switch plug and see if you have 12 volts on it. This plug
http://store.the-electric-connection...witch-p96.aspx
Just use a small wire with the ends cut back or even a paper clip.
Make sure you have power at the plug and you should be good to go.

C4ProjectCar

I did check the fuse, but thanks for the tip.
According to the FSM (and my experiences) you do have to short the low pressure switch on my particular model. If you don't it turns off the compressor when the computer detects there isn't enough freon in the system. The battery has to be reset before it will start again. This means the freon isn't getting circulated into the high pressure side, so it can't accept a full charge.
I have about 27 oz. of freon in there right now. I'm not putting any more in without some more research. It's running about 40 PSI on the low side and 105 PSI on the high. Although earlier I think it was at 290 on the high side.
When I turn off the engine I hear hissing coming from, I believe, the evaporator. Is this indicative of a leak?

Cliff Harris

I suggest taking it to an AC shop and have them use a sniffer on it to determine if you have an leak.

C4ProjectCar

The purpose of me working on this car is to learn, so taking it in is a last resort. I appreciate the advice though, and I will end up doing that if I can't fix it myself.
When we had it on a vacuum of 30" Hg the pressure gauge hardly decreased (well, increased I guess) over time. With a leak that small I thought adding some leak-stopper would take care of it? It certainly wasn't a big enough leak to cause this hissing noise, I don't think.

active1951

How long did it hold the partial vacuum? A few minutes, hours or overnight?
I put the refrigerant can in hot water while loading it to system, even with empty system, never needed to "short" anything on any vehicle.

Blue Vert 91

"jumping" the low pressure switch fools the system into turning the compressor on. It should have some oil in it for lubrication but the whole point is knowing what the operation low side pressure is so you can get the evaporator to see 35-45 psi. Just adding a can might not get your pressure up above the low side pressure safety switch.

C4ProjectCar

It went down by 2" Hg in about 3 minutes.
I've heard of putting it in hot water before. That's probably faster.
I'm not sure if it's because I have the C68 automatic climate control, but I had to short the low pressure switch to get the compressor to run.

Blue Vert 91

In the residential world we use a micron gauge and the gauge might bury itself in 30 seconds but it still might take an hour or 4 to clear itself. If there is moisture in the system it has to boil off and clear itself out and we shoot for 500 microns. Point is the longer you pull a vacuum the dryer/cleaner the whole system is.

C4ProjectCar

That.

C4ProjectCar

That makes sense. I'm not sure the conversion, but I believe the boiling point of water is around 29.9" Hg, right?

Blue Vert 91

gosh I have no idea, obviously in a vacuum water is going to boil more rapidly and there is a glide as the vacuum increases it takes less temp to make it boil but what those numbers are I have no idea. I'm sure someone has a chart on it LOL.
I'm surprised the auto world doesn't use a micron gauge at all.
It will let you know if you do have a leak because you will watch the microns go down then the system will gulp some air and the gauge will pop back up. Then you get angry and realize you have to go the other way with NTG and soap bubbles.

C4ProjectCar

I'm guessing the professionals use a micron gauge but I'm just using a manifold gauge set I have. You can still see if it's leaking because the needle will move up over time (which it slowly did in my case).

desertmike1

The boiling point of water is Altitude (pressure) dependent, at 29.92 HG [730 mmHg] water boils at 212°f

C4ProjectCar

It appears I've introduced some confusion. I meant 29.9" of vacuum, not 29.9" of pressure.

whalepirot

My local A/C expert says leaks in C4 condensers are common. unless you have the proper tools, NO procedure can be accomplished properly, so either a sniffer of some visual indicator (dye) can properly find a leak.

FWIW, I learned recently that R12a is superior to and compatible with both 134 and R12, while costing much less. My shop, tho, recharged my system with R12.

cudamax

A system needs to be sucked down to -25 to -30 and the longer the better. So as to pull out as much water as possible. Then the gauges need to be closed, tight and you need to wait a good hr or more to see if it comes up towards Zero. If it holds down there then, it shouldn't have a leak. Then and only then should it be recharged.
Sucking it to only 1 or 2 is not good enough.

Blue Vert 91

Ya 29.92 is a perfect vacuum, gauges show deep vacuum but rarely does anyone actually achieve perfect vacuum , even on home systems. They are kind of like unicorns