JD 3720 Air Conditioning line pressures?

   / JD 3720 Air Conditioning line pressures? #11  
Most R 134a systems use a low pressure cut off switch and a high pressure cutoff switch. If you are low on freon, they will tend to cycle on and off. So if it is shutting down, may be over charged, or condensor/ radiator dirty. Blow out and wash out, condensor and radiator cores. Also check evaporator core and cab filter, blow out if dirty. You can check an auto repair manual, for guage readings. R134a works best at exact charge, too much or too little makes a big difference. If you are low it is best to reclaim, evacuate air and moisture from system and add the exact charge. Look for a decal on or near a/c with charge amount, or check your manual.HF has cheap air powered vacuum pumps, evacuate for atleast 15 min.
 
   / JD 3720 Air Conditioning line pressures? #12  
hizoot and Dr Dave both make good points imo. One of the common problems I see is overcharged systems because lots of junior technicians seem to misdiagnose and add freon. I agree with using guages to watch the low and high sides and use clamp on Fluke thermometers but not everyone has the tools and know how to accurately diagnose their ac system. So unless you have the tools and skills needed and have 44F air at the ducts I would leave it alone.
 
   / JD 3720 Air Conditioning line pressures?
  • Thread Starter
#13  
I bought a set of gauges, hooked them up, ran the tractor up to 1500 RPM. The low side held at 50 PSI......and the high side climbed, climbed......and then the compressor cut off.

Plugged system? I bought a new drier and expansion valve. Hoping its not the compressor (tractor is a 2007).

Am I headed down the right path?

Thank you
 
   / JD 3720 Air Conditioning line pressures? #14  
JDneophyte said:
I bought a set of gauges, hooked them up, ran the tractor up to 1500 RPM. The low side held at 50 PSI......and the high side climbed, climbed......and then the compressor cut off.

Plugged system? I bought a new drier and expansion valve. Hoping its not the compressor (tractor is a 2007).

Am I headed down the right path?

Thank you

Generally, if the compressor on a 134a system is cycling on and off rapidly, I've almost always found it to be an overcharge condition... Usually, undercharge will prevent the compressor from cycling on at all, though not always. Bleed off some pressure(environmentalists scream here) you might be surprised.
 
   / JD 3720 Air Conditioning line pressures? #15  
you low side pressure is good, but as far as the head pressure rising could be a good number of things. be sure your condenser is completely free of dirt and debris,if its plugged you can give it an acid wash to clean it out. sounds to me like its all in your condenser, whether it be a bad fan or dirty condenser. the good thing is there is nothing wrong with your compressor if that were the case your pressures would be equlized. good luck bud! P.S. dont dump any refrigerant thats not a good idea unless you know you overcharged it but it doesnt sound like that to me with 50lbs suction. If idid that it would cost me 10k and jail time and lose my career.
 
   / JD 3720 Air Conditioning line pressures?
  • Thread Starter
#16  
I thought about that, though the low side is holding right at 50psi....about where it needs to be. The high side is where the pressure is ever increasing until the sensor cuts out the compressor ( takes about 15 seconds until cut out from turning AC on)...that leads me to believe there is a plug in the system somewhere. The gauges read 50 PSI with the tractor shut off (about where the A/C charge should be).

Any thoughts?
 
   / JD 3720 Air Conditioning line pressures? #17  
what is the temperature coming out of the vents? did you take a temp reading yet. Unless i missed it somewhere in this thread. Just saying becuase obviously we dont have windows that open and close wondering if this cycling is becuase of the temp reading and you are just now noticing the cycling. Maybe a normal condition. I have blacked out windows so even last week in 100 degree temperatures, my machine was on fan setting number 1 and freezing cold. Doesnt take much with these machines with small cabs and cooling capacity to get to temperature and start cycling a/c compressor
 
   / JD 3720 Air Conditioning line pressures? #18  
with your system running what does your head pressure climb to before tripping out? when the unit is not running your pressures should eqallize and be the same on both sides of the system. i dont believe its a plug in the system, but not able to get rid of the heat in the condenser. not sure how your system is set up but do you have an independant condenser fan
 
   / JD 3720 Air Conditioning line pressures? #19  
AC is all about thermodynamics and pressure/temperature relationships. If you do not understand the principles involved you are just stabbing in the dark and changing parts hoping for a solution; gets expensive. Refrigeration/AC is a complex trade that does not fit into the DIY realm. Yoy have already spent as much as a professional diagnosis would have cost and not done yet. In my younger days refrigeration was my trade. Been away from the nuts and bolsts for 30 years and it has not gotten any simpler. I would even be leery of a tractor mechanic as a diagnostition unless he has extensive training/experience on AC. We always hated following the part changer mechanics as it was hard to collect any more money from the customer when he had already broke the bank and still no fix. Bite the bullet and take it to an expert.

Ron
 
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   / JD 3720 Air Conditioning line pressures?
  • Thread Starter
#20  
If this small fix doesn't do it.......I'll take it in to an AC shop. Any recommendations in the Milwaukee area/Elkhorn Area?

Thank you for the excellent input
 

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