Don't know this one.......?????

[skippy]

Well I can try the soap trick, what do you figure, about 4 drops of detergent to 16 oz spray bottle? I know on vacuum leaks on the engine I use about 2 drops of dish detergent to 16 oz spray bottle of water.

yeah,try it.we actually buy a solution at the a/c parts stores called big blue.buy the spray bottle and i gal refills.we use it for natural gas leak detection too,works like a charm.if you got a leak,and you still got system pressure it will work.don't be afraid to put a little more soap in the bottle.

 

[MAKG]

100 PSI with the engine off?

This thing is WAY overcharged. Recover the refrigerant, then fill with 80% of R-12 capacity. NEVER top it off. My guess is, that's what the previous owner did.

If you want to be thorough, flush it out (to get all the crappy stop-leak out), and replace the orifice tube and accumulator/drier.

 

[thegoat4]

100 PSI with the engine off?

This thing is WAY overcharged. Recover the refrigerant, then fill with 80% of R-12 capacity. NEVER top it off. My guess is, that's what the previous owner did.

If you want to be thorough, flush it out (to get all the crappy stop-leak out), and replace the orifice tube and accumulator/drier.

Could be that, but depends on ambient. Here in Texas, 100psi static is about right out in the damned sun.

http://www.csgnetwork.com/r134apresstempconv.html Chart at lower part of page.

You'd have to cram a LOT of liquid freon in there before the static pressure would rise.

He probably just has some air in it.

 

[MAKG]

That can't be right.

Static absolute pressure at a given temperature is inversely proportional to the charge by weight. You don't have to cram a lot in there; just in proportion.

And you can't make a PT chart without an assumption of volume. You can show RELATIVE changes, but not absolute. What's the assumption in that calculator? There is no standard charge volume; it's all over the map.

 

[skippy]

That can't be right.

Static absolute pressure at a given temperature is inversely proportional to the charge by weight. You don't have to cram a lot in there; just in proportion.

And you can't make a PT chart without an assumption of volume. You can show RELATIVE changes, but not absolute. What's the assumption in that calculator? There is no standard charge volume; it's all over the map.

mike,do you weigh in your charge,or put it in by guage pressure?

 

[MAKG]

mike,do you weigh in your charge,or put it in by guage pressure?

I weigh it. That's what the spec is.

 

[skippy]

I weigh it. That's what the spec is.

check your pressures when charging complete?

 

[MAKG]

check your pressures when charging complete?

Yes, but with the engine running (i.e., not static). Once again, that's where the specs are. This is to check the pressure switch adjustment and verify that high side pressures are not excessive.

Even if I did check it when charging is complete, a freshly charged A/C should be very cold due to adiabatic expansion (and really nonuniform -- though the compressor side of the condenser will still be cooler than normal operation even if it is hot to the touch), so that PT chart will be quite difficult to read. Of course, one could wait a bit... but without a spec, I don't see the point.

 

[skippy]

Yes, but with the engine running (i.e., not static). Once again, that's where the specs are.

Even if I did check it when charging is complete, a freshly charged A/C should be very cold due to adiabatic expansion, so that PT chart will be quite difficult to read. Of course, one could wait a bit... but without a spec, I don't see the point.

the guages are a pt chart.

 

[MAKG]

the guages are a pt chart.

No, they are the "p". They don't care what the temperature is. And they are at least somewhat dependent on the temperature far away from the test ports (the total weight of gas-phase vs. liquid-phase will strongly affect the pressure).

I'm afraid I'm not seeing where you are going with this. A PT chart would be useful to verify correct charging volumes, but to do so, it would have to be independent of the gauges.

 

[skippy]

they are p/t,notice the corresponding temp scale on the faceplate of each guage.thats why the temp scale is there,cross the pressure on a independent p/t chart and see if the guage p/t isn't fairly close.

 

[thegoat4]

That can't be right.

Static absolute pressure at a given temperature is inversely proportional to the charge by weight. You don't have to cram a lot in there; just in proportion.

And you can't make a PT chart without an assumption of volume. You can show RELATIVE changes, but not absolute. What's the assumption in that calculator? There is no standard charge volume; it's all over the map.

That calculator is crap, just look at the chart.

Static pressure is just the freon's vapor pressure. That depends only on temperature, not volume. A 1lb can, a 30lb bottle, or a 100lbs tank all have the same static (vapor) pressure at a given temperature regardless of how full they are. Within reasonable limits, anyway. That's why I said you'd need a LOT of freon in the system to upset the static pressure.

Keep in mind there's a phase change going on in there and it does quite a lot to negate volume differences.

So, you look at a system's static pressure when it's at ambient temperature, compare it with what the static pressure should be at that ambient, and you can determine if there's air in there. Some of the fancier AC recovery machines use that same rule to periodically purge air from the storage bottle.

 

[MAKG]

they are p/t,notice the corresponding temp scale on the faceplate of each guage.thats why the temp scale is there,cross the pressure on a independent p/t chart and see if the guage p/t isn't fairly close.

OK, I happen to be home sick, so I went downstairs and peeked at my R-134a gauge set. I stand corrected.

Though I don't know why anyone bothered with the high side scale. It's not going to work unless the whole system is at ambient (so high = low).

 

[skippy]

OK, I happen to be home sick, so I went downstairs and peeked at my R-134a gauge set. I stand corrected.

Though I don't know why anyone bothered with the high side scale. It's not going to work unless the whole system is at ambient (so high = low).

we use the hp scale alot in my trade,and the p/t chart as well.the p/t chart was recommended in this case as a learning tool,and they are free at a/c supply houses.

if ones guages are close to accurate,they can be used as p/t charts.the average shadetree mechanic is not wanting to know saturated evap/condensing temps,saturated suction/discharge temps,etc....