AC pressure?

[Ryan]

Just checked the AC. It was converted to 134. The pressure on the low side is around 44psi. All I have is one of those off the shelf cans. Seems to be running cool. Since it's hot as hell thought I check the system and put some refrigerant in the system and get it cooler..... I know the 134 is not gonna be as good as the r12 but seems to be working well. Think this is kind a high. Will it damage the system. If it is too high how can I bleed the system? Will the system get warmer if I lower the pressure?

This is measured with the engine running and AC on MAX.

 

[Nick Micale]

For the low side you should have a lower pressure, 20-25 psi, as that will provide colder air off the evaporator. At 44 psi on the low side , the system will not provide adequate cooling in a GN here on a hot day?

In the summer hot temps we can see hight side pressure well over 400 psi, and that we like to see lower for better cooling.

This is one reason that a GN must have an excellent cooling for summer cooling in the desert, and with 134a it is only possible unless some of the AC system components are also upgraded.

Be aware, if you over-charge the system it will degrade cooling system efficiency.

 

[earlbrown]

Before my dad became 'super CEO' and whatnot he was an HVAC tech in his 20's...

I remember him charging out family cars when I was a kid by 'chasing the frost'. Basically you'd have the hood up and the A/C running and watch the frost line. The trick was to have it end right before the firewall (evaporator). That would get you the absolute coldest heat exchanger without frosting over with an insulating layer.

Looking back it would have been kinda neat to know what the pressures were that lended to such results and how they compared to factory specifications.

 

[Raeban]

Your pressure seems high as indicted above. The pressures depend on ambient temp and humidity. This chart works well for a max target. High pressure relief is 410-450 PSI IIRC.

 

[Mike T]

Oil level in the system is often overlooked. Not knowing how much oil was or was not added in the past can be a real problem. Oil fowling (too much oil) will cause the system not to cool right or damage the compressor and too little oil will lock the compressor. This can go both ways with a recharge....if you keep adding refrigerant only to a leaking system the oil will eventually get low and if you keep adding the do it yourself kit that has oil in it the balance will go the other way.

 

[Mrneg9]

Here you go.

 

[49-blues]

I believe you re overcharged, at 90 degrees ambient outside temp your readings should be about 30 psi on the suction side and 175 on the discharge, higher pressures = higher temps , if you let some refrigerant out of the suction port down to 30 psi your temps will come down and your AC will get colder, licensed NYC refrigeration engineer.

 

[Ryan]

Current temp is 88 and 69% humidity. According to the chart....the pressure looks to be in range. Am I reading it right?

 

[49-blues]

You want your refrigerant temperature pressure to be around 32-35 degrees refrigerant temp to be able to take the heat and humidity out of the air.on the suction side. The discharge or high side is figured as an air cooled condenser by using the actual ambient temp and adding 30 degrees to it so apx 120 degrees on high side and then using a temperature pressure chart would give you about 175 psi on the high side and 30-35 degrees on the low side, take some gas out of the system and you will see the difference and be happy. I ve been doing AC work for almost 40 years.

 

[49-blues]

Look up Bitzer on the web and get a free chart for any refrigerant out there with correct pressures & temperatures

 

[Ryan]

Does it matter if I take out some refrigerant with the engine on or off? Know I have to read the psi with the engine on.

 

[49-blues]

You should run the motor with the AC on max.

 

[skidlid]

Just had mine converted to 134a and they installed 2.5 # instead of 3.2 # r12.

 

[Ryan]

Dropped the pressure down. Took a while. Had to purge, then pop the gauge back on and re-adjust the press switch. Not sure of the exact name. Thought it was the low press switch. Some threads call it a cycle switch. Had to chase it all around. Taped it with a screw driver a few times and it kept cycling on and off. Wonder if the switch is going bad? Is it a plug and play switch or do I have to purge the whole system? Looks like if works fine now, just drove around for a few hours and got down to about 45ish. It goes up and down when I'm driving around.

 

[49-blues]

It's the low pressure clutch recycling switch, the screw between the prongs can be turned to the left to lower the kick in pressure , it can be removed without any lose of freon. R-134 is 10% less Effecient than R-12 so it requires a 10% larger condenser to do the same cooling so by lowering the low pressure switch to the left you compensate for that 10% ineffeciency.

 

[Ryan]

Down to 30psi. Blowing about 39-50 degrees at the vent. I'm surprised it works so well. Thanks

 

[49-blues]

Lower pressures = lower temperatures, it may drop down alittle more once you get on a highway and get a good wind over the condenser!

 

[Ryan]

Yes, cruisin on hwy it drops to about 45ish....... once in a while it will touch 39.

 

[Ryan]

just tried to swap out the low pressure switch. refrigerant started to leak out. will i loose the whole system if I swap out the switch?

 

[49-blues]

There should be a Schreader valve in there like in a tire valve, it shouldn't loose the charge.