Engine Size: 5.0 L
Refrigerant Type: R12
Ambient Temp: 97
My friend's '93 mustang isn't cooling at all, so we hooked up a gauge set and took a look at the pressures.
At about 97 deg F ambient with blower on high and A/C on, we were getting vent temps of 95. Static pressures were about 64 psi (low), and 62 psi (high). When we ran the engine at idle (about 700 rpm), we noted that the compressor was cycling every 4-5 seconds. Whenever the compressor would cycle, the low side pressure would drop to about 23 psi before the compressor would shut off. At this same point, the high side pressure would go as high as 125 psi.
I suspect the low pressure cutoff switch was activating due to hitting the ~23 psi on the low side, and suspect that there is a restriction in the low side - my plan is to evacuate the system and check the orifice tube for restrictions. Is there anything else I should be looking at? Does the accumulator ever tend to clog in that kind of fashion? Thanks.
As an aside, the engine cooling fan clutch felt like it free-wheeled a bit - At the same ambient with a cool engine, the fan blade would spin a good 1/2 - 3/4 revolution when I flicked the blade. Is that a reasonable assessment? This is my first A/C repair. Thanks.
Edited: Sun June 15, 2008 at 10:03 AM by webbch
It's very low on refrigerant. I think that car uses a liquid tube that holds the orifice tube. Gotta cut it open to inspect the tube. Don't bother with the repair kit. Buy a new liquid line.
Thanks. So you're saying there's no non-destructive way to evaluate the condition of the orifice tube. Does it seem reasonable to suspect the orifice tube in this situation, or were you saying that it's most likely due to low refrigerant?
Should my first round of attack be to instead evacuate the system, and see if it holds vacuum, then recharge (with dye) if it does and check for proper operation and leaks before throwing any parts at the problem? Thanks.
You were right - low on refrigerant. I went to evacuate the system and pulled out only 0.2 lbs. I pulled a vacuum, and noted that it dropped off very quickly after closing the valves on the gauge - about 6 in. Hg in about a minute and a half.
Now I need to pressurize with R134 and find where the leak is coming from. Not sure which are the most probable areas, but will start in the engine compartment.
If that system held for over 10 years your friend was lucky. These systems leak badly from the o-rings in the snap-together garter-spring connectors. You may very well be able to simply R&R the garter springs and O-rings (coat with Nylog), vacuum and be all set. Stick with R12 !
Good luck, Dan
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