Is there an A/C diagnosis procedure thread?

[TW97C1500]

A/C not working.  Compressor won't come on.

 

I hooked up one of those gauges that comes with the recharge kits and it was on the high side of the middle of the range (low pressure port).  I did it at work using a coworker's gauge.  I didn't think to try it at the time, and didn't have my stuff anyway, but that evening I jumpered the relay and the compressor came one.  The air did not blow cold inside.  (Yes, on max.)  I jumpered the pressure switch on the accumulator and the compressor came on.  The high pressure line from the compressor got hot pretty quickly.  The lines going to the firewall didn't get even cool, and one of them is supposed to be cold.

 

I didn't want to run it too long.  My Jeep cold line gets cold pretty quickly.  I'm wondering if the orifice tube is plugged up.  A/C worked last fall the last time I needed it.  I bought the truck in late June and the A/C worked, but wasn't the greatest.  The '98 I had would freeze you out.  I mean, it was only 4 years old when I got it, but I had it for 11 years and got it up to 484,000 miles.  My current '97 would get real cold at night last summer, but during the heat of the day in city driving I had to have it on max (recirc).  Highway driving it would get cold enough I would turn the fan down.

 

I guess there is a high pressure switch too.  I need to know what to look for with the voltages to see if it is reading high.  Or maybe where else to check to see if it is triggering the relay off.  All the A/C shops are booked up for several days and the hottest days of the summer are predicted tomorrow and Wednesday.  I might get a flush kit if indications are that a line is plugged.  Well, I don't think I can rent a recovery set-up anywhere.  AutoZone has a vacuum pump but it just releases the freon.

 

EDIT:  Oh yeah, this really ticks me off  too because earlier in the Spring I had the grill off and saw that a lot of the fins were bent down on the condensor, so I spent several hours straightening fins and washing out petrified bug remains.  I was looking forward to improved A/C this Summer.  Stupid Advance Auto Parts has a real good price on a "fin comb", but it's website only and they won't do ship to store so it ends up being ridiculous with shipping to only order that.

[bronyaur]

In regards to those gauges that come with the recharge kit, they don't really tell you anything except that you can see the pressure increase as you add (or not if there's a leak).

 

The only way to check for a blockage without opening the system and visually inspecting the orifice tube is to attach a proper set of manifold gauges.  After letting the engine sit for several hours, without starting it, a charged system will show static pressure that should be even between the high and low sides.  If they are uneven, there may be a blockage.

 

If the compressor runs after jumping the low pressure cutoff switch, it's likely undercharged and/or has a leak.  A set of manifold gauges will tell you what you need to know.  

 

Now, depending on what the gauges say, what you do from there can go many directions.