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Discussion Starter #1
What are typical good freon pressures at 85F ambient for our cars (mine is an 05 Elise)? I think my low side may be too low. At 85F outside temp (and cold engine so no heat soak) I am getting 32/240 and a outlet discharge temp of ~60F. That is at idle with blower on high and recirc on.

I'm wondering if I have a bad or clogged expansion valve. I've tried adding freon, but it doesn't raise the low side much, mostly the high side and cooling didn't really improve.

Tom
 

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32 psi is not too low at all, but having the system at correct refrigerant weight and stabilizing it would allow you to better judge the performance. An evacuation and recharge to factory spec (1.25 lb) would be the first step. Get the engine up to operating temperature with the A/C on, then run it at about 1500 RPM's. Take pressure and a center vent temperature readings. Let it drop down to idle and check the same readings. Now you have a better idea of operational performance.
 

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It depends on the humidity as well, but 32 psi / 240 psi would be about right for 85F and 60% humidity. Discharge temp should be just over 50F, but 60F would be within the range of normal if there is no airflow over the condenser (only the fans).

On mine the evaporator design was horrible - lots of blow molded plastic riveting together with crumbling foam. The flapper doors did not seal well too. There were a lot of leaks, and since the heater core gets hot water all the time, hot air coming over from the heater was reducing the effectiveness of the AC.
 

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My trinary switch, which I tracked down to a 78 land rover part, failed, so I guess I took that out of my system.
 

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Discussion Starter #6
Thanks for the good info. I was using an R134A chart I found on the www which said the low side should be around 45psi at 85F. I guess mine isn't so bad after all, especially if I can get 60F at the center outlet with no airflow over the condenser and at idle (not 1500rpm).

I'd love to check out the evaporator housing for holes and leaks, but it will have to wait for another reason to do a major disassembly.

Tom
 

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These are all low side pressure readings with the AC running on Max AC
Ambient Temp in F--------Low Side Reading
65 ------------------------------- 25-35 psi
70 ------------------------------- 35-40 psi
80 ------------------------------- 40-50 psi
90 ------------------------------- 45-55 psi
95 --------------------------------50-55 psi
100 ------------------------------50-55 psi
110 ------------------------------50-55 psi
Michael
 

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Generally speaking the high side should be 2-2.5x ambient temp with the car at high idle (~1500rpm).

So 85* would be around 170-210psi. Low side isn't so much a concern, if the system is working correctly and the high side pressure is correct they the low side will be fine.

To correctly charge the system, you need to charge it by weight after pulling a vacuum on the system.
 
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