Best would probably be to talk to an HVAC shop. They should have the required filling quantities for your A/C.

If a leak is suspected they can add a dye to the refrigerant which becomes visible under UV light.

Just cautiously wash down the A/C parts and engine bay around the A/C components. Else other contaminants could cover up the traces.

If the filling was still the original one it would mean it had not been refilled for 12 years then being low on refrigerant could be an easy fix. About the time I would expect it to be low but still do some cooling.

Good luck with the fix.

 

Low refrigerant typically causes excessive cycling of the compressor at higher engine speeds (not at idle). In the line on the inlet side of the compressor (at accumulator) there is a cycling switch that opens when the pressure drops below a certain pressure and then the compressor shuts off. This is a bit oversimplified, since in our Blazers the computer ultimately controls the compressor. However this cycling switch is there.

My 2001 Blazer was giving me intermittent fits of the A/C not working for a couple of minutes and then it would be OK for a while and then not, and so forth. Strange thing was that it cooled really well when it did work. Ended up replacing this cycling switch because it was closing (or not closing) at different odd pressures. The old switch was full of compressor oil when I took it off, and I suspect that was what caused the problem. Put a new one on and no problems thus far this Summer. Point is - you really need a set of gauges and some knowledge to effectively work on A/C. Dumping in a can of Freon is not always the solution.

 

I have just measured the temperature at all four vents. 54 degrees F at all vents.

 

Here is what you vent temps should look like. How long is the cycling on and then off at idle and do your temps meet this chart?

If the cycling is the cause of the problem then there are a number of causes: low, low side pressure (low refrigerant, faulty orifice device, weak compressor valves), high, high pressure (too much refrigerant or restriction), faulty low side switch, faulty high side switch, faulty PCM, faulty clutch, faulty cabin temp sense, .... I can walk you through any of these circuits to test if needed.

Les and others are right though, a set of gauges along with the vent temps will get you the proper info for a diagnosis.

The entire refrigerant circuit has oil circulating throughout so any device that is removed is greasy. As a matter of fact feeling around any connection point for an oily residue helps find leaks.

Again, adding gas might be the solution but there are many other possible causes and more gas can cause problems if not the issue. One of my last failures was a compressor not low charge.

George

 

The ambient temperature was 70 degrees at the time of measuring the vent temperatures, not sure of the humidity, but around 40% sounds good. The truck was sitting in the driveway idling when I took the temperatures and the A/C remained on set to Max A/C, it did not cycle off at all.

According to your chart, GeorgeLG, the vents are NOT delivering cold enough air, yet when the A/C is on, it cools quite adequately!

 

My bet is that the cycling switch is malfunctioning as happened to Les Myer. I have also read elsewhere that this switch was somebody else's culprit under similar conditions.

Any ideas?

Exactly where is that located and what is the part number and the procedure to replace it.

 

It's located on the accumulator, pointing towards the engine on mine. Just get one from your local auto parts store. They're cheap. Screw the old one off, screw the old one on. Don't have to discharge A/C system. Easy Peasy!

FYI the temps in the chart is for temp of air entering the A/C condenser in front of the radiator. For the pressures and vent temps to be valid, you need to set a fan in front - and temp of this air needs to actually be measured. Also the engine needs to be run at a specific RPM. But I will say that your system seems to be cooling if your air is getting down to 54 degrees.

 

Thanks, Les, I'll change it and report back the results.

 

you need to have the charge checked by someone that knows a/c systems. under charge=bad cooling. over charge= bad cooling. plugged orifice tube= bad cooling. are you seeing a pattern here? the a/c pro cans are a joke. oh , and by the way the front of the clutch has a plate that is sucked into the pulley magnetically when the compressor is engaged, so yes the front plate will move back and forth. getting the temps from the vent when the a/c is set to max and high fan will be telling. it should be 45-55 degrees plus or minus a few, depending on outside temp and humidity. good luck with your endeavor.