A/C basics
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Tuned
Joined: Mar 2004
Posts: 400
Likes: 2
From: South Texas
A/C basics
I was searching the forums and after reading through hundreds of posts, I am a litttle confused. I read that the low side should read mid 30's to low 40's and high side should read between 225-250 depending on ambient temperature. If the low side reads high while the compressor is running at max a/c does this indicate too much fluid or lack of. If the high side reads high or low what does this indicate? How does the high side pressure reading depend on ambient temperature (higher outside temperature higher pressure reading?)?
Lead Driver
Joined: Jun 2004
Posts: 6,343
Likes: 588
From: Amarillo, TEXAS!
The higher the low side pressure, the more refrigerant in the system, and the higher the temperature of the evaporator. In other words, the an undercharged system will actually produce colder temperatures, but is more likely to ice the coils. The whole thing is a balancing act.
The high side pressures will increase as the ambient temperature increases. A basic rule of thumb is 2.2 times the ambient temperature for the pressure, but it isn't set in stone. If the high side reads high, it usually indicates lack of cooling across the condensor coils. If the low side reads high, it can indicate overcharge, or flow restriction in the system. Ideally, if you can get the evaporator down to 34F and keep the compressor from cycling on and off, that's perfect. It doesn't happen often, though.
The high side pressures will increase as the ambient temperature increases. A basic rule of thumb is 2.2 times the ambient temperature for the pressure, but it isn't set in stone. If the high side reads high, it usually indicates lack of cooling across the condensor coils. If the low side reads high, it can indicate overcharge, or flow restriction in the system. Ideally, if you can get the evaporator down to 34F and keep the compressor from cycling on and off, that's perfect. It doesn't happen often, though.
Junior User
Joined: Jan 2003
Posts: 79
Likes: 0
From: St. Louis
Engine rpm can also change pressures as the compressor sppeds up and slows a bit this is why it has the pressure switches and clutch etc. Under higher rpm the high side can rise a bit and the low side can drop a bit also pressures are different for r-12 and r-134
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