Automotive Air Conditioning Information Forum (Archives)

yorled on Sun May 15, 2011 2:29 PM

Year: 97
Make: toyota
Model: corolla lx
Engine Size: 1496
Refrigerant Type: 134a
Ambient Temp: 87
Pressure Low: 120
Pressure High: 125
Country of Origin: Japan

ozsI have added oil and vacuumed the system to 38 and 3/4 of negative pressure and after adding 8 0zs of refrigerant I noticed my
gauge was reading 120 (retard) with both low and high side of the gauge closed and engine off.

My problem is that i do not know why the gauge should be reading so high.

N:B When the engine and the AC is on the high side reads 160 and low side 70 .

GM Tech on Sun May 15, 2011 2:52 PM

Air in the system will do that- it is a compressible, not a condensable, as refrigerant is. So you must have let a bunch in after your vacuum- never heard of negative 38 pressure-- the best vacuum you could ever do is to overcome atmospheric pressure- which depends on where you are at and is usually near 28 In Hg.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

mk378 on Sun May 15, 2011 3:10 PM

With the engine off and enough of a charge to have some liquid in the system, both gauges will read the saturation pressure for the refrigerant at the car's ambient temperature. If it's higher than that there is air in the charge.

NickD on Sun May 15, 2011 4:10 PM

If I read this right, perfectly normal if the blue and red hoses are connected to the respective ports. Because closing the valves closes between the gauges and the yellow hose, not between the gauges and their respective hoses. When first connecting the gauges to a charged system, have to be darn sure both valves are closed first to check pressures. Or else all of the refrigerant will be blown out the yellow hose or its port if not connected.

No units of measurement are given, but if measuring in psi, reading 120 psi would be perfectly normal on both gauges with the valve closed and the blue and red hoses connected to the gauge ports and the the AC ports. This is static pressure and at 120 psi, the refrigerant temperature would be at about 98*F.

If the AC port hoses are disconnected, most of the R-134a gauges have check valves in them, to read zero, have to disconnect those hose from the manifold. But not good to that that until you remove those hoses from the AC ports first.

There is a whole host of units of measurement for pressures, USA sticks with pounds per square inch, pascals are the international standard with numbers in the millions. Also metric measurements in either grams or kilograms per a unit area such as a square centimeter or even a meter for extremely low numbers. British like using atmospheres, bars, or tors to add to the confusion.

For vacuum, we use inches of mercury, how many inches a column of mercury will rise in a vertical glass tube. Really would get a high number by switching that mercury to water, but we use water for very low pressures. For inches, can use millimeters or centimeters of change. Noah, in the Bible used cubits when charging his ark. Bet you didn't know his ark was air conditioned.

yorled on Sun May 15, 2011 9:39 PM

Quote
Originally posted by: yorled
I have added oil and vacuumed the system to 28 and 3/4 In Hg and after adding 8 0zs of refrigerant I noticed my

gauge was reading 120 (retard) with both low and high side of the gauge closed and engine off.



My problem is that i do not know why the gauge should be reading so high.



N:B When the engine and the AC is on the high side reads 160 and low side 70 .



Edited: Sun May 15, 2011 at 9:45 PM by yorled

NickD on Mon May 16, 2011 7:29 AM

Sounds perfectly normal 28.75"/Hg, only 8 ounces of refrigerant, engine off, both high and low side gauges connected, both valves closed. You are reading static pressure!!!

Even surprised when you started your engine with only eight ounces your compressor even engaged, very marginal. Must be at idle for your high side to go up to 170 psi and your low side dropping to 70 psi. If you increased your speed to 2,000 rpm, your low side would drop close to zero. But not good to run it that was, not enough refrigerant to adequately lubricate your compressor. Have to bring that low side quickly up to at least 24 psi by adding refrigerant, and at 2,000 rpm.

NickD on Mon May 16, 2011 9:11 AM

On second thought, if your engine was cold, measuring 120 psi static pressure is quite high. Sounds like when you switched from vacuuming to charging, you got a lot of air in the system, if this is the case.

yorled on Tue July 05, 2011 8:06 AM

I am in the process of revacuuming the system and after four and a half hours(4 1/2 hrs) it's at 27 in Hg. I think the time is a bit too long so is there a way which i can speed up the process so i can get 29 in Hg?

mk378 on Tue July 05, 2011 8:58 AM

Pull vacuum on just the manifold with the hoses disconnected from the car. It should go to full vacuum almost immediately. If not, the pump is not working very well or there is a leak in the manifold / hoses. You are using an electric mechanical pump not an air-powered venturi device, right? The air-powered ones never develop sufficient vacuum, don't use it.

yorled on Wed July 06, 2011 7:56 AM

There are two access ports on the pump but only one is used at any time so i found out that the cover on the unused port was not closed tightly so i did the obvious thing and within ten minutes(10 mins)the gauge was at twenty eight and a half in Hg(28 1/2 in Hg) ,this is a much better result but is it good enough and can it be better ?

Thanks in advance.

yorled on Wed July 06, 2011 8:07 AM

Please note that the new measurement was obtained after removing the hose/s from the car.

yorled on Sat July 16, 2011 6:00 PM

What is wrong when the sightglass has a milky white /or creamish look ?