A/c proper psi

[jacobsen]

My can of 134a has a gauge on it with a trigger. It's the blue bottle with the NASA label on it with the trigger. I bought this one because it allows you to add and remove refrigerant if you need to. Obviously to remove you would need a bucket of ice water... I've been adding and removing here and there and trying to figure out what the optimal PSI is. Right now it's about 92 degrees in Minnesota and according to the gauge on the refrigerant can the PSI should be somewhere between 50 and 55 PSI. I've been experimenting to see how low I can go because I know that there's a sweet spot with a minimal amount of refrigerant gas making the evaporator coil work extra efficiently. I saw in another post old guy says anywhere from 25 to 45 PSI is optimal. But like I said the can suggest 50 - 55 in 92 degrees. But somehow that just seems a bit High.

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[old guy]

50 to 55 may work when the ambient is in the 90's but I suspect you will find that the A/C doesn't work in the morning at a lower ambient. I suspect you will have to bleed off a little refrigerant when the ambient drops.

BTDT.

[jacobsen]

I actually think my comparison from 55 PSI down to 40 PSI shows that 40 is better than 55 even in this temperature.

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[old guy]

I actually think my comparison from 55 PSI down to 40 PSI shows that 40 is better than 55 even in this temperature.

That appears to be my sweet spot as well when the ambient is in the 90's.

[jacobsen]

That appears to be my sweet spot as well when the ambient is in the 90's.

I'm down to 30 PSI and this might be better than 40

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[old guy]

I'm down to 30 PSI and this might be better than 40

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It will be interesting to see how that works when the ambient is in the high 70s or low 80s. I suspect you may find that you don't have enough refrigerant when the ambient drops.

[Audibot]

It's the blue bottle with the NASA label on it with the trigger.

It may say NASA, and was probably using technology originally developed by NASA, but I don't believe this refrigerant is any more special than others.

[jacobsen]

It will be interesting to see how that works when the ambient is in the high 70s or low 80s. I suspect you may find that you don't have enough refrigerant when the ambient drops.

This seems contradictory to what the gauge seems to indicate. Higher ambient should equal higher psi according to the gauge. So i would think it should work for lower ambient temps? Hmm

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[jacobsen]

With the motor off its equalizing at about 110 PSI on the low side port

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[jacobsen]

When I was running at 45 PSI the pressure would drop to 37 PSI when I applied the gas. I sucked the gas back into the can with some ice water and now I'm running 28 PSI at idle and about 26 when I hit the gas.

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[Kevin C]

When I was running at 45 PSI the pressure would drop to 37 PSI when I applied the gas. I sucked the gas back into the can with some ice water and now I'm running 28 PSI at idle and about 26 when I hit the gas.

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See if this helps...

http://aircondition.com/tech/questio...ith-Gauges-FAQ

[jacobsen]

See if this helps...

http://aircondition.com/tech/questio...ith-Gauges-FAQ

Good article... Looks like the freezing point of r-134a corresponds to about 27 PSI? 27 psi will cause the condenser to reach freezing in other words.

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[ryanj]

Ok so this is just my opinion / experience so take it for what it worth. I have an AC machine and have played around with charge levels on several cars to see what works best. I recommend sticking to factory charge levels for best performance in all conditions.

Low side readings on a good system should not drop below about 32 psi any lower and you are going to start freezing and having issues with the system cutting out. On a really hot day at idle with the engine compartment completely heat soaked you are probably going to see low side as high as 50-60 psi. Your low side reading is going to be pretty close to the temperature of the air right at the evaporator. If you measure at the center vents its going to be about 5 ish degrees warmer than your evap temp.

Running your low side 28-26 psi is going to cause problems not only with freezing , but you may not be fully utilizing the evaporator with it undercharged that much.

If you goal is to just experiment with different charge levels to achieve the best cooling I would not get hung up on the PSI numbers I would be more concerned about the actual temps coming out of the vents as there are so many variable to change the pressure readings.

[old guy]

This seems contradictory to what the gauge seems to indicate. Higher ambient should equal higher psi according to the gauge. So i would think it should work for lower ambient temps? Hmm

You are correct. The pressure is lower with a lower ambient. If you are already down to 30psi with a high ambient you may find system starts to freeze up at a lower ambient.

[seanf86]

to do this properly you need a manifold guage set to check your high side pressure as well, just using the low side is a recipe for problems as pressure changes depending on fan speed inside the car as well. The low side guages are great for getting the system working and cooling but to really dial it in high and low side pressures need to be watched as a slightly plugged orifice tube can really change the numbers.

[jacobsen]

to do this properly you need a manifold guage set to check your high side pressure as well, just using the low side is a recipe for problems as pressure changes depending on fan speed inside the car as well. The low side guages are great for getting the system working and cooling but to really dial it in high and low side pressures need to be watched as a slightly plugged orifice tube can really change the numbers.

I put a brand new orifice tube in about 2 years ago. But when I put it in it slid further past the indentation. I've got a manifold gauge set. What should the high side pressure look like?

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[jacobsen]

The a/c article says high side should be 2.2 - 2.5 x ambient.

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[seanf86]

high side is dependent on ambient temperature, you need a pressure temperature for chart for r134a
here is a pressure chart

here is high low chart



I use an infrared temp gun to monitor the low and high pressure lines on the car as well.

edit http://aircondition.com/tech/questio...ith-Gauges-FAQ

this is really helpful as well.

[jacobsen]

My psi suddenly jumped to 150 psi today! Pegging my lo side gauge... compressor would not turn on. I put a new restricter valve on 2 years ago and it got sucked past the indentation on the lo side pipe where it sits. It went thunk and i knew it slid in too far, i suspect its in or near the 90 degree elbow passed the indentation. Wonder if thats causing my issue?

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[seanf86]

with the compressor off and the system equalized it should be about 150 psi, you need to figure out why the compressor isnt turning on.

[jacobsen]

with the compressor off and the system equalized it should be about 150 psi, you need to figure out why the compressor isnt turning on.

Compressor came on when i restarted the car. Psi with compressor on is 100psi. It was 28psi last week. Is my coil freezing up? I'm still thinking restricter valve is an issue.

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[seanf86]

Compressor came on when i restarted the car. Psi with compressor on is 100psi. It was 28psi last week. Is my coil freezing up? I'm still thinking restricter valve is an issue.

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sounds like somethings restricted somewhere, I'd pull the orifice tube and check the lines under the car for bends or kinks, esp if you are running no belly pan, that line that goes under the oil pan is subject to getting crushed.

[jacobsen]

sounds like somethings restricted somewhere, I'd pull the orifice tube and check the lines under the car for bends or kinks, esp if you are running no belly pan, that line that goes under the oil pan is subject to getting crushed.

I have an aluminum panzer shield. Love it.

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[jacobsen]

I keep having to adjust the pressure down. It's like everytime it gets hot there's too much pressure in the system. So I keep having to use a coffee can of ice water and open up my 134a can to let some back in and relieve some pressure. I've done it every week I just did it now. But if I want my AC to work that seems to be what I have to do. It was over 90 degrees earlier today and it was blowing mildly cool air until I let the car run for an hour. And it began to get on top of the situation just slightly while parked in the shade.

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