Charging A/C System with 134a - Pressure Swings when Compressor Clutch Engages

[DavidProehl]

I had a fitting on my A/C system that was leaking, I know this because I could clearly see still wet and oily UV dye present. I have since tightened the fitting and am crossing my fingers that it is no longer leaking. As a result of the leak, my A/C clutch now frequently engages and disengages (engaged 2 seconds, off 2 seconds). I bought a pressure gauge and a couple cans of 134a to top it off, but am noticing when I hook it up the pressure swings wildly: about 25 psi when the compressor is engaged and 60 when it isn't. My target pressure is about 35 psi given the current temperature here. I'm sure I need to add more 134, but am scared to do so with such a high pressure reading when the clutch isn't engaged. Am I ok to continue to add more? Am I doing something wrong? This is my first time charging an A/C system.

I am following the instructions on the package:

Turn on car and A/C to Max
Connect gauge with 134a can attached
Check pressure
Open valve and add 134a into system
Close valve and recheck pressure reading

[DavidProehl]

Ok, scratch that. Apparently that behavior is normal. Found YouTube videos with that happening. The rule of thumb is to only use the low reading. Good to know. That high reading can be a scary one. I continued charging and found that the high reading became lower, and the low reading became higher. Now, the system is fully charged and blowing cold once again. So far, no sign of a leak where it was before. It might actually be a sealed system now!

[David T]

If you have a leaky connection the only proper way to fix it is to take it apart, remove the "O" ring, clean away any corrosion, replace the "O" ring, oil it all up with some refrigerant oil, put it back together and leak test. Mix up some soapy water and spray it over the connection while the A/C is running and look for bubbles. You added -134, how did you know there is -134 in the system already? It is not good to mix different refrigerants. Over tightening connections can strip the threads. These connections do not normally loosen up by themselves.
David Teitelbaum

[DavidProehl]

I replaced my evaporator last year, and this is the connection going into the evaporator that was leaking. The rather embarrassing part of the story is that I replaced the evaporator myself, then took it into a shop to have the A/C charged (already converted to 134a). Didn't realize just how easy it was to do the charging. The A/C worked all last summer, but then I fired it up this season to find that it had leaked, apparently as a result of me not tightening down the connection enough because it was a challenge to access. Had a bear of a time getting any tools in there to tighten it, but when I did I got maybe a fifth of a turn out of it. I'm hoping that was enough.

[jawn101]

Hey David, hit up Clint- he still has all my A/C tools (pump and manifold gauges) - you guys can probably get a lot done with those! :)

[DavidProehl]

Good suggestion Jon, will do if needed. I think I'm ok though. I used the simple system with just the low pressure fill, will I have problems not having used a full manifold gauge set? What is the advantage there? I assume it removes more air from the system?

[jawn101]

Good suggestion Jon, will do if needed. I think I'm ok though. I used the simple system with just the low pressure fill, will I have problems not having used a full manifold gauge set? What is the advantage there? I assume it removes more air from the system?

Well the manifold gauge lets you watch high and low pressures at the same time while you add to the system. It's just a little more informative than a low-pressure only one. But if you're blowing cold, not cycling too frequently and don't see any leaks then it doesn't matter if you used a voltmeter and chewing gum! :)

[DavidProehl]

Ok, cool. TBD yet on the leaks, but it was fine after running for 20 minutes and sitting for a couple hours. Will run it again today and see how things look. Feeling optimistic.

Also, as long as we are talking A/C, does anyone else have the issue where the A/C only blows super cold when the engine is running above 2,000 RPM? Does that indicate a compressor on its way out (mine is original) or is that normal operation? It's cold below 2,000, but not nearly as cold as above 2,000.

[Ron]

Could be OK itself, depending on how hot the coolant is and the even voltage to the blower etc. for maximum performance. Or, you could have a bad compressor, poor engine coolant performance, blower performance, due to duct flaps/vacuum leaks, charge etc, etc....

Perform the pressure checks at N:09:01 in the Workshop Manual and go from there.
(Be sure to use a box fan in front of the radiator and take readings as clutch drops out ).

(Most of the older systems improved off idle...sounds like you may just need to tweak your charge and attack the next project ;-)

[David T]

A manifold gauge set gives you access to the low and high sides. It also allows you to monitor pressures. It is VERY important to monitor the high side pressure. From that you can tell if there is air in the system or if there is moisture and the system freezes up. An experienced tech can get by without that by checking temperatures of different parts of the system but measuring pressure is a lot more direct. You can also assess the condition of the compressor by watching the high side pressure. You will know when the high side pressure is way too high, the relief valve will pop. That is there just in case the system freezes or the cooling fans fail. The relief will pop before the high side safety switch will stop the compressor. If the relief doesn't pop then the safety switch should shut you down before you blow the hoses.
David Teitelbaum

[DavidProehl]

Thanks for the tips, sounds like a full pressure test is in order rather than just testing my low pressure A/C line. Not something I'll get to in the next week, but I'll add it to the ever growing list.