I thought the A/C was working really good and it was for 30 minutes or so and then the vent temp. began to rise. The fan was on 5 (no recirc). I checked the accumulator and it was frosty. The ambient temp. was about 75F and the low pressure side was 55PSI at idle and 40PSI at quite a high idle. The compressor never cycled (since the pressure remained too high?). I think the pressures are roughly correct??

This is a Copart car and I do not know the history.

What happens if a system is filled with R134a without evacuating the system? It seems to me the pressures could be high if the system wasn't evacuated and the system was just filled with freon enough to get the pressure up. So even if the pressure was about right, there could be too little freon which could cause frosting. Does this sound right?

Mine: 3-940s running, 2-740 and 1-940 parts cars, and 3 1959 John Deere 630s (1 for parts), dtr1:3-940s, dtr2:1-740, 1=940

Hello,

In very very low freon condition the metal line to the evaporator PLUS the accumulator would frost BUT the suction pressure would be below 30PSI.

Adding more R134a without knowing the current total charge would risk of blowing up the system.

Generally the pressure in the system correspond well to ambient temp with AC OFF. If the ambient is 70F then the pressure is around 70PSI. If the ambient is 80F then the pressure is around 80PSI. Just connect your gauges to the low side valve beside the accumulator to measure this (with AC OFF). If the pressure is way below the stipulated value then your system maybe low.

There's no accurate way to measure the available charge in the system VIA reading pressure ALONE as pressure goes up and down according to ambient temp. To only way to ensure accurate charge is the system must be evacuated and recharged with the specified weight.

Hope this helps,
Amarin.

Thanks Amarin, I put the gauge on the low pressure side this morning and it read 107PSI and the temp. in the garage was 67F. Would you recommend just bleeding off some R134a (I have an empty tank to capture some) or should I empty the system and recharge? I'm leaning toward emptying the system, drawing a vacuum, and recharging? Does anyone know whether the ambient temp.=low side pressure works with the R134a replacement (old R134a 30 lb container = R134a replacement 12 lb container)?
--
Mine: 3-940s running, 2-740 and 1-940 parts cars, and 3 1959 John Deere 630s (1 for parts), dtr1:3-940s, dtr2:1-740, 1=940

Hello Jd620,

Looks like the charge is way too high in your system. I'm leaning towards emptying the system, vacuum and recharge back. This is to eliminate further guessing as to what is the current charge after you've emptied some. Further benefits is that if the A/C still performs poorly after proper recharge it would be easier to suspect fault in other components.

Using R134a replacement is not recommended as per FAQ (Heating and Air Conditioning). It may give you more cooling but there may be some incompatibility issues with the system components (i.e seal leaks, compressor not receiving proper lubrication, etc).

The FAQ recommends use of smart orifice tube. I have tried this and yes there is much more cooling especially during idle. But my smart orifice tube gave 'farting' sound when the compressor kicks on and again when it kicks off. Tried empty, vacuum and recharge the system again. Same results. In the end I used back the fixed orifice tube and enjoyed a quiet drive.

Regards,
Amarin.