Air Conditioning Pressures?

[RTillery]

I have a set of R134 gauges available and would like to check my 04. The AC seems to be functioning ok, but the cooling is marginal. It only seems to get somewhat cool after maybe a half hour of running and I am thinking my refrigerant charge is incorrect. Can somebody give me the high and low pressure operating ranges. Thanks.

 

[frijole]

Supply Air Temps

Per the '03 service manual, the system is designed for a leaving air temp, (supply air temp) @ diffusers of 45*F. Gone are the days of 38-40*F air, although my '03 does get close to 40*.

Suction pressure should correspond with refrigerant temp in the evap which should be 7-10*F colder than actual leaving air temp. Head pressure runs a little higher than R-12 @ any given ambient. Depending on design criteria of the condenser, (20* delta is +/- is "normal"), you take entering air temp @ condenser, add 20*F, go to head gauge and read temp, then read directly to pressure. Your needle should be right there. There are variations on automotive applications though. It depends greatly on what the radiator fan is doing. If it's just spinning, expect the head to be somewhat higher than you calculated. If the fan is engaged, head will be lower. Clear as mud, eh? Hope I didn't confuse you too much. Ron

 

[radar doctor]

Thanks

for the info.

 

[CumminsBu]

I got this from A/C Forums www.ackits.com



R-134a Pressure Temperature Relationship



Pressures shown in the charts are provided as a general guide and may not represent your exact readings. Ambient temperature is measured 2 inches in front of the condenser.



Low Side Readings

(PSI) Evaporator Temperature (Fahrenheit)



16-29 psi/ 33-50 F

19-39 psi/ 33-60 F

25-43 psi/ 40-65 F

37-51 psi/ 48-65 F



High Side Readings

(PSI) Ambient Temperature (Fahrenheit)



115-200 psi/ 70-80 F

140-235 psi/ 80-90 F

165-270 psi/ 90-100 F

210-310 psi/ 100-110 F



Hope this helps

 

[RGardner]

My a/c doesn't seem to be cooling like it should. Has anyone else noticed and had the dealer check to see if that is as good as it gets or maybe a low freon problem?

 

[txhawg]

I complained to the dealer, and it turns out I was 1 pound low on Freon. They charged it up, but it is still not as cool as I would like it to be

 

[C Schomer]

I haven't done much auto AC for over 30 yrs. but most cars since the late 70s have an orifice tube and I've charged them just like any other AC with a fixed expansion device - by superheat. Read the saturation temp on the low side gauge and compare it to the suction line temp that comes out of the firewall, before the accumulator. If the suction line is 10* warmer than the low side saturation temp. - it has 10* superheat. If the temps are the same, it has 0* superheat - the evap is full or could even be overcharged. A full or nearly full evap is ideal. I like to charge to 1-2 degrees superheat as long as the head press. is staying in the ballpark. I don't know why the auto mfgrs don't train on any of the old methods that are used in the non-auto AC world. Craig

 

[kaprice]

MY AC WASN'T COOLING AT ALL UNLESS YOU WERE DRIVING DOWN THE ROAD. THEN WHEN YOU STOPPED IT WOULD GET WARM AGAIN. I TOOK TO DEALER AND THEY SAID THE SYSTEM WAS LOW. THEY EVACUATED THE SYSTEM AND CHECKED FOR LEAKS. THEY SAID NO LEAKS AND REFILLED IT. IT STILL DOESN'T SEEM TO WORK ALL THAT GREAT. GONNA HAVE IT LOOKED AT AGAIN WHEN IT GOES IN FOR NEXT SERVICE.

 

[Kilby]

Funny... my father in law is an ex Ford AC mechanic (now works for me) and he was just checking out my '03 last Friday. Mine can get as low as 38* but on occasion, it won't cool down while sitting still and idling. I can't duplicate the conditions at will but it does happen. The compressor clutch starts cycling faster than normal indicating a low freon condition but the 38* temps say otherwise. I think I'll have him add some R-134 anyhow to see what the outcome is.