'94 A/C Overcharged!?!?!

[TedJ]

I bought my truck back in September and when I bought it the A/C worked slightly. It acted like the system was low but it was not hot out and I figured I'd mess with it in the summer when I needed it. It got warm a week or two ago and when I turned it on I got nothing at all. I figured I'd get some r-134a and charge it up. So i went to charge it and hooked up my gauge set. I looked to see if there was anything left and the low side gauge was off the scale. High side reads about 92psi. Compressor will not engage.

At this point i felt like I was in lala land and decided to check the system on my parts truck (which has working a/c dof!). With it off i had 65 PSI on both sides, and 28-30 on the low side and 100-110 on the high at idle with the ac on. So I know its not my gauges.

But then what is it? Is 92psi with the system off too high for it to engage? (its a lot higher than the other truck) Or is that right for this system and one of the pressure sensors is busted? Whats going on here?

Thanks Ted

 

[shamaal]

Clearly a number of things wrong.

1. What are the pressure with the truck off? Pressures should equalize, if not suspect obstruction, usually orifice.

2. Pressure switch is on accumulator and closes at 47 psi, engaging compressor. The compressor should be running.

3. I guess overcharge is possible. I don't remember what the at rest pressures are and it's too late for me to go out and hook up gauges, maybe someone else will recall. Too much refrigerant increases danger of liquid in your compressor; liquid is non compressible. I'm reluctant to recommend jumpering the switch to start the compressor.

If it was me, I'd give serious thought to replacing the orifice and accumulator (good practice), evacuating and reloading.

On the plus side, it doesn't sound like a leak. The pressure switch doesn't look good though, take the connector off and measure the resistance, it should be short at >47 psi.

Keep us posted.

Wear eye protection.

 

[TedJ]

My reply here got wiped out by the database problems so I'll repost it...

To Clarify:

...the low side gauge was off the scale. High side reads about 92psi.

The pressures on both sides are equal, but the scale on the low side gauge doesn't go up to 92psi, so I said it was off the scale.

Also, is there a high pressure cut out switch somewhere that is keeping the compressor from engaging? What is the standard at-rest pressure for an explorer (with R134a) that is correctly charged? I want to make sure that its not overcharged before I start troubleshooting the electrical.

Thanks Ted

 

[Glacier991]

I doubt overcharge....As you noted at rest the system pressures will equalize.... the resultant pressure will be dependent on ambient temperatures... and really not tell you much about overall charge. My guess is your low pressure cutout is bad. I'd hook the gauge set and start it up with the low pressure switch jumped... see what happens.

 

[TedJ]

I finally got some time to look at my a/c yesterday. I unplugged the connector on the low pressure switch and it was full of oily goo and this green stuff. So I cleaned it out as best I could and plugged it back on. The a/c started running and I took it for a short test drive and all was well.

Then today I flipped it on during my drive home and it got cold and then crapped out totally. Nothing. So now i'm back to square one.

I think I'm gonna replace the pressure switch first since it looks crappy. If I take it off, is there a valve that will keep the refrigerant from coming out? I think there is but I want to be sure before I get a little surprise when I take it off

-Ted

 

[Glacier991]

yes. There is a schrader valve behind it. I'm betting your switch has failed.

 

[TedJ]

There IS a schrader behind that thing, but nothing says that it has to close properly. I did the nascar version of low pressure switch replacement. Unscrew, then OH, S@&T and rip open the package and get the new one on as fast as possible.

After that bit of fun, Glacier you got it right on. Switch was shot. I added a can of R134a (mainly to make up for what got out) and now its cold and frosty. Now hopefully it will stay that way...

Thanks to everyone...yet another problem solved by help from this board.

-Ted

 

[91explorer1009]

Where can I purchase a new pressure switch? Is there a site online that sells them for a 91 ex?

 

[TedJ]

I got mine at pepboys. It was like $9.00. They have a different name for it in the computer though... something like cycling switch or the like. Its the only switch they have listed under the A/C section though. Its not worth ordering it online b/c the shipping will like double the price.

-Ted