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AC PSI question 740 R134

C

chronicrhythm

Member
Joined
Sep 28, 2012
Location
Colebrook, CT
I got my ac working recently but had a question about its operation. At idle it sits just below 40psi and then when the fan kicks on drops to 30-32. The question I have is that when I’m accelerating it seems to be short cycling. I tested this in park and had someone hold the pedal to around 2.5k rpm’s and the pressure of the ac dropped to about 18 and shuts the compressor off. Is that normal or is it technically short cycling?
 
What is the static pressure (engine off) with the engine cold? Please also post the ambient temp in degrees f. (to be more accurate, shoot the compressor with an infrared temp gun).
With R-12 and also with hfc134, the static pressure should be close to ambient temp in fahrenheit. It’s a coincidence that can help you see if it is under-charged or over-charged.
Usually, fast clicking is undercharged.
 
And if convenient, include the high side pressure when the low side hits 18-20psi, and whether the entire engine area is cool, medium, or hot.
 
mikep said:
What is the static pressure (engine off) with the engine cold? Please also post the ambient temp in degrees f. (to be more accurate, shoot the compressor with an infrared temp gun).
With R-12 and also with hfc134, the static pressure should be close to ambient temp in fahrenheit. It’s a coincidence that can help you see if it is under-charged or over-charged.
Usually, fast clicking is undercharged.
Click to expand...
I’ll try to check that tomorrow. Is there a way to check the hi pressure on the 740’s? I didn’t think they had a port for that. I’m not sure I have anything to check the high pressure as well. Think my gauge is only for low pressure
 
All systems should have a high side port on the smaller line or compressor, but if you only have a low side fill hose, don’t worry about it. If it’s cooling and not icing up the evaporator, let it ride.
 
mikep said:
All systems should have a high side port on the smaller line or compressor, but if you only have a low side fill hose, don’t worry about it. If it’s cooling and not icing up the evaporator, let it ride.
Click to expand...
Yeah it’s cooling pretty good. I just notice when the torque converter isn’t locked that it fluctuates on and off quite a bit and isn’t as cold but it is doing the job. Pretty hot the past few days where I am
 
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