Jd44A_1

Member
The other day I had posted here on info about the AC on a 4450. It has the original Nipendenso compressor R12 fittings but I have a conversion fitting to use my 134a gauges. I had found a leak and corrected that. Pressurized the system with my shop air to 100 lbs from a adaptor that I had made then snapped on my AC gauges and closed the LOW pressure valve and watched the gauge for almost 2 hrs. No movement on the gauge. So, I assume no leaks right ? This is all with the tractor not running. Should I have it running or will the compressor run with just shop air pressure ? I'm thinking it shouldn't but I've been wrong before. Any insight on this subject? I want to make sure that all leaks have been corrected before I charge the system with 134a. I had tried to vacuum the system for a hour but it would go down to negative five psi for a short while then the gauge would go up to a positive 7-8 then repeat. It would still hold 100 psi for 2 hrs tho...
 
You are correct for pressuring up the system looking for leaks,, but you should not be using shop air,, there is too much moisture in shop air. I use compressed nitrogen, it is an inert gas with no moisture,,I pressure up to 250 psi and use soap and water in a squeeze bottle to look for leaks,, then draw the system down to recharge with 5 small cans of Freon.
 
Thanks Tim, Do you think I still have a leak somewhere because my AC gauge will hold 100 psi for 2 hrs but I cannot get it to vacuum down to neg 5 or below then my gauge will raise back up to almost 8 psi then hold for a minute thego down to negative 5 hold for a minute or two then climbs upto 8 again...I'll get a different set of gauges and try it again later today.
 
A leak can show up more under vacuum or pressure. Your problem now is you blew moisture into the system. You aren't going to boil all that water out quickly with a vacuum. It's saturated. Let the pump run for a day at least with new oil. If it doesn't pull down to -29 and hold it's still leaking.
 
My gauges or pump which is a HF $20 red air vacuum pump cheap pos but works may be leaking when it's running trying to get a vacuum.
 
I almost chimed in on your other post telling you to charge it with 134A to check for leaks if you do not have nitrogen available. The 134A is not that expensive and you are
doing this for a neighbor so pass the cost on to him, definitely better than introducing all that moisture into the system from shop air. You apparently have not had any training or studied much material on AC repair. After an hour on a vacuum pump there should be nothing that raises the pressure in the system back up to 8 psi all refrigerant should be boiled off. What do your gauges read when unhooked and the hose ends and hand valves open? Should be zero and if not reading zero they need to be ..zeroed.. If they are quality gauges they should have zeroing screws on the faces behind the dial covers. The thing about pressure checking using the ..hold method.. with air or or compressed gas is that a small leak can go undetected because the expand gas is like a spring in a way, that can have some minute movement yet hold basically the same pressure. Sure it checks for major leak but that is about all.
 
Shop air is a bad idea because even a little bit of moisture in an Au statrt/C system is a lot. When running the vacuum pump, watch the color of the oil, if it becomes the slightest bit milky, you need to change is as water laden oil will reduce the pump's efficiency. If the oil does not turn milky, but you cannot pull a deep vacuum, you still have a leak. You also need to zero out the gauges before you start because a leak should not cause a vacuum reading to go to 8# or so of pressure.
 
Yes, it does seem like you do have a leak,,the higher pressure that you can achieve with compressed nitrogen (up to 250psi) would probably make the leak show up,,and I know not every one has a compressed nitrogen tank on hand, but it is useful in many ways to test high pressure lines and the like .
 
I found the leak. Last year the HP hose was replaced and the HP switch didn't get tighten up. As for the gauges going wacky it was caused by the Schrader valve in the suction hose on my gauge set. I removed that and now all is well. It pulled a vacuum down and held at -28ish for a hour and half...I replaced the drier and charged it with refrigerant. A nice 42F....Thanks for the help...
 
I found the leak Tim. It was the HP switch that didn't get snugged after the HP hose got replaced last year. Pulled a vac on it at -28ish yesterday and it held for hour. Replaced the drier and recharged with 5 small cans of refrigerant and got a chilly 43F at the vents....All is well. Thanks for your help...
 

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