I'd start with some gages and my experience with the cheapo sets is that they're good maybe once - then a hose will break loose - usually just after pulling a vacuum so it sucks in a bunch of air and you lose a new Dryer.

Reclaiming is seldom necessary - you usually don't start working on it until it's empty (and all of your neighbors and friends will bring you empty systems). Go to a shop and have them suck out what's in it.

Buy a scanner instead (if you don't have one; if you do, hook it up and get the high side). Your system relies on a Pressure Sensor which is a thermistor screwed into the high side. The PCM sends it a 5 volt reference and the return is proportional to pressure (about 1 volt per 100 psi) and the higher the return, the higher the pressure. Anyway, the PCM expects that return voltage to increase when the compressor cranks on so you want to see what it's giving back and the only way to do that is with a scanner (or you could back probe the signal wire but putting a hole in insulation doesn't do much good on a device that relies on resistance to send a precise signal).

Scales are nice - better for the big jobs like the Central in your home. You'll need a different license for that and it's a sit down, proctored test - not the quickie online for your 609 - go here for more: www.epatest.com

There's a whole gamut of vacuum pumps. With a big enough compressor, you can get by with a $9 displacement pump from Harbor Freight Tools. More info and a reasonble starter kit plus a great board at www.ackits.com - it's where I go when I get stuck.

 

Atta boy......

 

After re-reading your last post, you may just have a bad connection at the Low Pressure Switch - fairly common for early to mid 90's GM's. A low gas code is generated when the PCM detects rapid cycling or on/offs at the Low Pressure Switch and you don't have that code. If it's just staying off (open) that just means it's too cold to crank on the compressor (low side below 25 psi) - no code is set. Wriggle the connector around - try holding it onto the switch - connect and reconnect it a couple of times (worked for me on a truck I use to own which would always quit when it was 100 or better) - check the wiring. Solution is usually the switch and since you replaced it (assuming you get it running with one of the above) it could just be the Connector or wiring.

 

You can find out everything you need to know about auto air conditioners on this web site. www.ackits.com I read this and ordered a few parts from them and changed my S10 over to 134a and I think it actually worked better than it did with R12. They were very helpful.

 

Tried the scanner auto xray 3000 and 91 coupe no data about ac pressure just on off stuff.. First thing I checked was the switch contacts as i have fixed a lot of things by fixing connectors rather than buying parts. The switch had 15 ohms across the terminals when closed and enough current to light a test light not enough to pull in the 3.6 ohm clutch coil. 14.99 later switch works. Real problem for me is it blows coler now but 55 on a 76 degree day does not seem that cold I would think sub 50 should be possible or am I chasing nothing?

 

I just wanted to comment that my low pressure sensor went bad within a few months of being converted to 134. Took me a while to figure out. I was told that these old style sensors have a problem with R134, but the new one I installed has been in there for a couple of years and is ok so far.

I believe there is an adjustment screw on it to help with the lower (or is it higher) low side pressures with 134?

 

Your scanner should spit out the Pressure Sensor reading in volts and/or convert it to pressure. A high side of 2.2 to 2.5 times the temp of the air across the Condensor is a good average. Design of most systems (cooling fans) keeps it around 200 psi at idle and low speeds.

You need to know the Evaporator temperature/pressure. R134 is 32 degrees at 28 psi. With superheat, the Evaporator is actually warmer than that, but you need to know what the pressure is; convert that to temp and then add 8 to 10 degrees for superheat to come up with a ballpark figure. Know that and you can add or subtract to make things better. And since pressures are dependent on ambient air temp, it's best to do this when it's 80 -85 degrees. Get it right there and everything else will probably be as good as it can be.

Low Pressure switch is adjustable and R134, because it freezes a few degrees less than R12, will perform better by reducing the cutout threshold to 22.5 psi. You do that by pulling the Blower Motor Connector while observing the Low Side Gage. A screw between the terminals can be turned counterclockwise to reduce the threshhold - clockwise to raise it.

 

I was wearing a White shirt when My a/c stopped working....I never wear white shirts anymore....I like my A/C working

I was listening to 95.5 KLOS when some guy rammed into the back of my RX7.......I erased 95.5 from my presets.....I'll never listen to them again......

 

As I am sure you know 1000 times at least more about ac than I do..LOL that ac site you directed me to has gage sets for sale would you be kind enough to pick one out for me that will last fine for the once a year or so use but has enough value to give good info to use reliably and not fall apart I want it to last as I am more of a quality vs price but don't want a pro setup for the tech that has to use it every day for the next tens years... i would really appeciate it.

From your post I get the following I adjust low side pressure switch by disconnecting blower motor and oberving on low side pressure where compressure cuts off if too high greater than 22.5 psi I turn the screw on low side sw CCW if too low CW until it is 22.5 psi. Plug blower motor back in and do the check on temp vs high side psi and need to be temp times 2.2 to 2.5 equals high side psi if high side is too high I am assuming over charged aqnd lose some gas and if too low under charged add some and please correct me if i am wrong.. is omewhere around 2.35 the sweet spot or go a bit lower if not cold enough to get to 2.2 and if very cold or frosting get closer to 2.5??? At 2.35 an 85 degree day is 200 psi and 85 easy to hit here..LOL..
what is a 134 target number for good average cooling at the center duct? 45 50?

To throw a wrench into all of this I have realized I have an underdrive pully on crankshaft made a other post aboutit asking for stock L98 diameter for pulleys.. PO seemed to like to play with hop ups that might make some power cheap but at a comfort cost or just a waste of money.. anyone want an airfoil..LOL.. found that a while back by accident.. knowing that i will stick a matchbookcover between the idle set screw and lever so the idle is 1000 insead of 700 something seem reasonable while testing?

BTW found the screw for low side psi sw in plain sight...
Dave

 

As to gages, anything sold on the ackits site should be ok.

Underdriven pulleys puts a monkeywrench in everything - with the stock pulleys, compressor doesn't reach max output until at least 1200 rpms and knocking down the pulley speed at idle/low speed is going to muck up performance.

Low to mid 40's at the Center Vent on a 70 degree day would be a good number.

As to pressures, there's allways a slight difference between cars (at least all that I've owned and I've never owned one that had an a/c system that didn't break). Fine tuning is a juggling act but when I charge, I start with a couple of cans and then start monitoring things until it's right for me. For my Vette, that was 38 degrees at the vent on a 68 degree day with the low side right around the cutoff threshold of 25 psi (which is where it's set for R12). Once it's 70 or better, it's warmer and at 100 degrees, it's into the 50's - but a 50 plus delta on a 100 degree day still feels pretty good (and most charts put the vent at 60 on triple digit days). If I lived in the desert, I'd probably go with a slight undercharge. Undercharging isn't always wise - the gas carries the oil that lubes the compressor and it's going to cycle a great deal more once it's below 75 - 70.

The Low Side should never ice up - that's what the Low Pressure Switch is for. It cuts power to the compressor when the gas drops to 32 degrees. The threshold is set below the saturation pressure because the gas is superheated in the Evaporator so that it won't flash back into a liquid. If you see ice, the Low Pressure Switch is either misadjusted, faulty, or you've got something other than pure gas.

Trust you've checked that the Temp Door is completely shut? Might want to do that while you figuring out what gage set to buy.

Don't monkey with the Minimum Idle Screw (unless someone allready did!) No amount of vibration will cause it to change from the Factory Setting. Any air flow problems through the Throttle Body are always something else - usually because it's gunked up (or someone thinking it needs to be adjusted). Put a quarter or something else between the throttle linkage and stop to hold the rpms above 1200. Jumper the Low Pressure Switch Connector so that the compressor won't cycle off (if low, you'll see some ice). Make sure the fans are running and take a look at your pressures.

 

Not to but in but, what scanner is SunCr refering to? I to need to get tools.

 

I use an Auto Xray - one of the originals - and when the Vette goes it goes with it because it's the last of my OBD1 cars (and I seriously doubt I'll ever own anything else without a warranty anyway).

You can download software and use a laptop - go to Scan & Tune.

 

The final resolution to this problem. They did not get all the old oil out when doing the conversion to R134a and the combination of the two different ones plugged the accumulator. They did a very thorough flush changed accumulator and oriface tube did a comeplete evacuation and recharged with correct oil. 45 degrees at a 78 degree day at 1200 rpm.. Life is good and proved to me that while not as cold possibly quite acceptable for CT at least. I am going by what they told me so if BS it is but the system works correctly and my final goal. Another system on the car working correctly and can be crossed off the 'task list. The next 4 a tuneup, fix antenna, find out what the whining noise is from serpentine belt drive, get correct stock puley back on so it chages corretly and get better ac yet possibly though not in this order.

 

Paul; I'm having the same problem. Can you look at my 88? It's been converted to R134 and it's not blowing very cold air. PM me please with directions and I'll bring it in to your shop.

PM sent: sorry for the highjack.