I am looking to figure out why my a/c isn't working this year. It has worked perfectly until this year. I first noticed the problem this winter when the defroster wouldn't clear the glass, but I shrugged it off, hoping it didn't have to do with the a/c system.
Now that the temps have been in the 70s, I have had a chance to try out the a/c, and it doens't change the air temp coming out the vent at all, not even a little.
I can hear the compressor cycle, and can tell when it places a load on the engine, so possibly the compressor is still good?

I picked up an R12 pressure gage that is able to test high and low pressure sides of the system, but didn't come with any instructions. I need to know how to test. Should the engine be running with the compressor engaged, or off?

I think the static pressure, engine off that is, has to be over 80-90 PSI or the compressor won't operate. (You can take this reading on whichever port is easy to reach.)

An easy check on f12,put your gauges on after the car has been sitting for a while so all temperatures are the same.The temperature and the pressure will be about the same with the car not running.When you start the engine the suction pressure will drop and the head pressure will rise.If the pressure gets to the shutoff point of the low pressure cutout and cycles at that pressure,then you are low on freon.If the head(output)pressure rises too high the high pressure cutout will shut off the compressor.(This not likely)I don't usually work on air conditioning,but I believe GM cars have 1/4 inch flares on the suction port and 3/16 flares on the discharge port.If I can help,email me your phone number and a time to call and I'll help over the phone.

Static pressure is right at 80psi. The schreader valve on the accumulator is leaking too. Once the plastic cap is loose/removed I can hear the valve hissing slightly. Is it possible the pressure is too low to kick the compressor on?

yeah, that's entirely posible. That's allot of why those caps are on there. The pressure is probably below the low switch pressure and now the compressor won't activate.

You have a couple choices.

purge the R12. fix the valve. recharge with R12 after fixing that valve.

Purge the R12. replace the seals. replace the accumulator/dryer and recharge with R134.

Keep in mind ACC/Dryers are only rated at a 7 year life. you should replace the ACC/dryer not fix the valve.

Total cost of conversion at this point isn't a whole lot differant than just fixing the valve at the current cost of R12.

Also keep in mind Fiero has the cooling capacity of a much larger car. Any loss of cooling you get will with R134 probably not be noticable.

Good info Ogre. I've spent this entire week at book stores, all the local libraries, the net, everywhere trying to research automotive a/c systems. Even the big blue GM books by MOTOR that I use for referenece quite often at the libraries, have very little a/c info, and most of that info was useless.

You touched on my next question. Is it worth the added costand work of switching to 134? I know it is safer for the environment, can be legally handled by untrained people(like me), but I wonder which of the two is more "efficent". Meaning, does one blow colder than the other, or does one somehow sap more driveline power? I've seen a lot of people on here switch to 134, but I have wondered if that were the best idea.

I will probably replace the accumulator and drier, since I figured if I had an a/c leak I would replace them with new, glad to know what the expected life span for them is.

Is there a way for me to test to see if the compressor is activating or not?

My son's 88GT was converted to R134a and believe me there is ample cooling.

You can legally work on the system after is is purged of R12 by a licensed tech.

you need to replace the ACC dryrer, the orifice tube, and preferably all the O rings.

I checked pressure this morning after letting the car sit overnight. Pressure at 68F is right around 61psi. Pressure must be too low to kick on the compressor.

Do compressor hoses have much of an expected life? Or do they typically last forever. Should I leave my compressor alone? If I open this system up, I don't want to do it again for another 13+years.
Should I play with the evap core or leave it alone?

Lots of questions, I can't find this info anywhere else.

According to the photocopies I made from the MOTOR books at the library, at 70F ambient temp, pressure readings should be near 126psi. A significant difference from my readings.

One last question for you guys. I stopped at AutoZone and got pricing for parts. For the "orifice tube" they had two listings for my compressor. One was $2.00, and one was $25 and it was listed as "optional automatic adjusting orifice tube". Which do you recommend I use. I have decided that price is litle object with this car since I have no plans to get rid of it ever.

[This message has been edited by fiero56 (edited 04-07-2001).]

I believe that the 126 psi reading at 70 deg is with the system running not static.

You caught me fill. I just double-checked my poor quality photocopies, and that is at 1,750rpm with system running.

Bringing this back up from the spider-webs of second page .

I am going to try and set up an appointment at my favorite dealership on Monday to have them evacuate the system.

Is there anything else I should replace while I have the system open? I am planning an accumulator and expansion valve replacement along with o-rings. Is there anything else I should play with? Compressor, condensor, evaporator core, etc? Also, any recommendation on which expansion valve to use mentioned in earlier post above?

I used the $2.50 expansion valve when I converted to 134 and it cools great! Take your time and replace all the o-rings. Some are a pain in the rear, but after 13+ years they need to be serviced.

You can get replcatment caps for the fill valves that have o-rings in them to seal leaky shraeder valves. I got by with this band-aid for several years on one car until the compressor finally let go. I got a pack at AutoZone for a couple of bucks. It was one of the HELP Blister Packs.

I've converted 4 of my cars to R-134 without any problems or noticable difference in cooling capacity. The largest car is an 89 Bonneville. After 4 years it will still freeze you out of the car. This is with a rebuilt a/c compressor also.

R-134 is not as effecient as R-12 but most systems are so over-designed you can't tell the difference. I believe a typical car a/c compressor is equivalent to about a 5 ton home unit. Think about it. A house seldom has to cool a 120 degree interior (as you might see in a car sitting closed up in the bright sun) in a matter of minutes to make a car comfortable.

Good luck,

Carroll