Low Pressure A/C reading

Hey all,

After the engine pull my freon was a little low, it could only keep up if garaged first. If it got hot after driving or was outside in the sun, it could not cool it down. At least not in a reasonable amount of time. So today I put one can of 134a in.

It seems to be working just fine afterwards, cold now but my pressure reading on the low side is now 40 PSI when I turn everything on full blast. I had read that 30 was normal so is 40 a problem? Or do I need to relieve some of that pressure?

Everything was working ok before, and it never got worse, it was just weak after we got everything back together.

Any comments welcome!

The temperature of the evaporator (and thus the lowest possible temp for the cold air) is determined by the low-side pressure. Approx 30 psig is the usual target, but for R-134a, 28 psig is about 32 deg F, 30 psig is about 35 deg F, and 40 psig is about 45 deg F. Goals include having the desired low pressure, but still having enough refrigerant and refrigerant flow to keep the return line to the compressor cold.

Having non-condensibles (air, water vapor, etc.) in the system lowers efficiency, as does too much oil.

Cool Wally, as usual you provide more than just a yes or no...I appreciate it. I have always had others look at A/C issues, so I wanted to get my feet wet on something simple.

If desired, can I just release a little to reduce the pressure?. From Low or high side?

By the way I am going to get a gauge manifold so I can see both pressures etc. this weekend, and then go from there.

It is illegal and a terrible environmental boo-boo to release refrigerants into the air.

If desired - sure.

Really, I figured there was a way to vent into something from a gauge set.....you mean there isn't? hhhhmmmm seems like there should be since I am sure this is not the first time it has happened to someone. I bet they do exactly what we are not supposed to do. ....sounds like a invention waiting to happen? I assume there are professional ways to do it, but why not something for the DIY? Probably won't get Gov approval though....but if they really cared...

Finally here are the numbers
Ambient temp 80
Humidity 80
Low side 25
High side 175
Engine warmed up from idle
Temp at vents 60+

Lost some pressure fiddling with the hi side connector, realized it has the r12 fitting still! So I had to go buys conversion connector. It is also by the receiver/dryer up front and not easy t get to for me.

Anyway it looks a little low now, the generic tables say at 80 it should be 40-50 low and 175 to 210 on high. But I thought 28 to 30 on r134 was good?
Yes, I am also assuming there is ware vapor or air in there making things less efficient. Next step will be to get it properly evacuated and recharged. But I still would like to come up with good target numbers (ignoring somewhat the temp it is blowing out the vents for now.)

Ps I deleted my previous post because it sounded more catty than funny sarcasm and did not add much value... Sorry about that.