GTM stage 2 Air Conditioner Problem?

LafitteZ

cool thanks

hindi1973

hi guys can anyone post their expereince in hot states above 110f regarding the low side and high side ac pressure results ? i am limited at the time being for the high side pressure gauge and most shops around me only can see the low side which is approx 32 to 35 psi , but the ac still gets hot in stop go traffic . so before i take action with bigger than fans , i am doing sams advise ac 101 , i have a feeling the high side is either too high or too low , or the 32 psi low side is also too low for our 130f weather or gets too high when the compressor kicks in .

all your help is appreciated

brand new 2012 twinturbo 370z nismo , approx 40's row oil cooler ,csf radiator , distilled water with water wetter , coolent temp is either half exactly or one dot below , oil temps is usually 210 to 220 in our 130+f weather

jm1fd

I don't have experience with R-134a systems in ambient temperatures that hot, but I do have experience with R-134a systems in general. It wouldn't surprise me a bit to see high side pressures of 300-350 in 130 degree ambient temperatures. Low side under those conditions would probably be in the neighborhood of 40-50.

A/C getting hot in stop and go traffic sounds like it is cutting the compressor because the high side pressure is too high. If it is only in stop and go traffic, then you have insufficient airflow through your condenser, or the air you're getting into your condenser is too hot.

I assume you have one or more intercoolers in front of the condenser? Where are your air filters located? Are they pulling in cool air or hot air from the engine bay? If they're getting hot air from the engine bay, the intercooler(s) are dumping that excess heat straight into the front of the condenser, and that is suboptimal to say the least.

hindi1973

well i have an appointment at one of shops that have the gauge for both low and high side , i sat in the car for 45 min in 120f weather infront of the house and it was cold as hell till the oil temps reached 220 and the dots are in the middle and most it reaches is one dot past middle , so i guess when i go there i should wait till it starts reaching those temps and test it , because if they test while its cold it might not be too hig or too low , its a twinturbo setup so i yes their is a big as% intercooler and the filters are on the sides behind the bumper , the solution which alot agree on and its a fact twinturbo setups,turbos,superchargers on those cars need bigger fans period , stock ones are not doing the job so spal fans will be replaced soon with high cfm and another fan behind the cooler , all will be with a thermo swtich .
thank you for ur sharing and help , finally someone shared or said something .

hindi1973

jm1fd, wht pressure do u think the compressor will start cutting off if its too high or too low on the high or low side ?because from my knowldge the low should be 32 to 40 max and high side should be doublt the ambient temp the car is in so if its at 130f , the high side should be 260 to 300 max , but the qustion is wht pressures should we avoid leavin the car in

jm1fd

Shop manual says:

- Approximately 3,120 kPa (31.8 kg/cm2, 452 psi) or more (Engine speed is 1,500 rpm or more.)
- Approximately 2,740 kPa (27.9 kg/cm2, 397 psi) or more (Engine speed is less than 1,500 rpm.)

You can't just say "double the ambient" because the P/T curve of R-134a is non-linear, rather it is somewhat parabolic in nature. Pressure increases faster as temperature goes up.

The factory shop manual calls for a high side pressure of 185-227 psi at 104F ambient. This indicates a condensing temperature of 125F-140F, so the factory is saying your effective condensing temperature is going to be ~25 to 40F over ambient. 130F + 25 to 40F comes out to 155 to 170F which works out to 281psi to 340psi.

Systems should not be charged by pressure. They should be charged by refrigerant weight. Do not decrease the charge below the factory spec, if you do, you'll get poor oil return to the compressor, and eventually it'll trash it.

hindi1973

thank you so much for the info and feedback

jm1fd

What you're describing makes it sound like the heat coming off the back of the oil cooler is what is just enough to push things over the edge. Fans with more airflow should help.