2005 AC low pressure port way high psi?

Might check the inverter coolant pump.

Look in the inverter coolant reservoir for movement on the liquid surface, or feel for a vibration on the inverter coolant pump.

 

What is the low side pressure when the compressor is off; and what is the low side pressure when the compressor is on?

When the compressor is on, the low side pressure spec is 22 to 36 psi with ambient air temp at 86 - 95 degrees F, temp set to MAX COLD, fan speed high, doors open. Under those conditions, the high side pressure spec is 199 to 228 psi.

On my 2007, with ambient air temp 105 degrees F, I found the low side pressure with the compressor off was 105 psi, and 42 psi with the compressor on and the air conditioner running correctly. There is occasional, very slight bubbling in the high side sight glass which shows me that the refrigerant is not over charged.

I have found that very little added R-134a will swing the air conditioning functionality widely.

What could cause the low side pressure to be too high: someone overcharged the refrigerant; or the compressor is not working properly, The latter would be the case if you found the high side pressure was too low.

 

Patrick did a great job of summing up the a/c systems operation and pressures at the said ambient temperatures. That should give you a great idea of a properly functioning system and in general, what numbers you should see and when. Sligh variations in the numbers can be expected from one system to the next....

Your statement of "hearing that 55psi is what you should see on the low side" is too high. That is not a good number for proper cooling.....and remember, high/low pressures will change based on ambient, fan speed and humidity/load on the system. In general, at 80-100deg ambient, you should see somewhere between 25-45psi approximate on the low/cold side. 55 would indicate a problem to me. High side/hot side would be around 200-240psi.

What are your vent temperatures while running the a/c system on max cold, recirculate, windows up/doors shut and what is the outside temperature while you are doing this? Also, what is the high side pressure reading and what is the low side pressure reading at this time? Have you verified that the electric compressor is kicking on under the hood?

To further extrapolate.....

There could be so many things going on and from the O/P's posting, we don't have enough info at this point. I have done tons of auto a/c work and one of the first questions I would ask is... is your manifold gauge set working properly and are you reading it properly? Since you are blowing hot air with a/c on (I am going to assume you have verified that the a/c compressor is on)..... it seems there IS a problem. Verify that the a/c compressor is on when seeing the high read on the low side. The low side will have higher pressure when the system is static with no compressor engagement. If it is on, and you truly are seeing those high pressures, then you have a definite problem in the system. I pay no attention to what my static gauge readings are on the high/low side generally as it tells you very little. What matters is what are those numbers when then compressor is on, the blower speed will affect them as will the doors being shut and the cabin closed off. The ambient temperature and humidity will also change those numbers. Use Patrick's information to properly assess the operation with the compressor on. The number one issue with all auto a/c systems is refrigerant charge. You need to make sure that you have the proper amount of R134A in the system. Oftentimes, since I have the ability to do it.....I just reclaim and recharge a system myself quickly to ensure I am dealing with a properly charged system off the bat and get that out of the equation because loss of refrigerant or overcharge are the TOP reasons for a/c performance related problems. Has anyone worked on this system recently or did this just happen out of the blue after the system has been working fine?

Further into the troubleshooting, many times when extremely high pressures are experienced in either side of the system, outside of a refrigerant charge issue, you have a restriction issue. There are only a few places in the system that can cause this. Blocked up condenser with trash(uncommon unless you have had a compressor blow apart), blocked up evap(very uncommon) and most commonly, the orifice tube or TXV has become blocked up(very common because of the tiny tiny holes in the screen). The orifice tube is located in the system where the high side (discharge) meets the low side (suction). It is the point in the system where the high pressure gas refrigerant from the compressor which has gone through the condenser and cooled to a cooler high pressure liquid. Then it passes through the orifice tube OR TXV(expansion valve) depending on whether the car uses an orifice tube or TXV setup(it's one or the other, not both). After passing through the orifice tube or TXV, you have a low pressure liquid that goes to the evaporator and ices down the core, allowing the air from the fan blower to be cooled as it passes through this "radiator" style device. Once that warm air hits the evaporator, the low pressure liquid refrigerant passing though it becomes a low pressure gas and is passed back to the compressor to start the cycle again.

In order to understand air conditioning you must understand all of the components, their purpose, the chemistry going on inside of the system and the proper diagnostic techniques. It is quite ingenious of a design and not at all something the average person will understand. I'd recommend using this information and seeing what you can find out. Post your results and we will see where to go.

Cheers

 

I just bought a 2007 Prius. The previous owner said that the air conditioner just quit couple of days ago. The low side pressure is pegged and the high side pressure is about 120. I don't know if the compressor is on. Please help! It's about 93 degrees outside. There are no codes either by pressing the auto and recirculation button and turning it on or through the torque app.