Another ac thread

[DosGatos]

gauge set at parts store was out on loan. go figure. system pulled in two small cans of 134. would have taken more but for now the air from the vents is cold. not a deep freeze but it's 100 out so not complaining. I'll read up on finding leaks to see what I can learn.
Found PT charts. That was good to know about so thanks for that tip iceman.

[smorgan87]

2 cans seems like quite a bit. Did ur can attachment have a gauge on it so u know what the low side is at?

[Rawze]

On my prostar with high rise sleeper(double bunk), after pulling a vacuum on the AC system, it takes 4 cans total to fill it up. I only ever put 3 in it because it runs colder.

[DosGatos]

(07-17-2018 )smorgan87 Wrote:  2 cans seems like quite a bit. Did ur can attachment have a gauge on it so u know what the low side is at?

Second can was to get dye in. Low pressure is in the range using a pt chart.
Ran the ac for about an hour. Went out at night with a uv penlight. Looked at everything except the sleeper evaporator. I'll open that today.

[DosGatos]

Couldn't find a leak and pressure is holding. Replaced missing linkage on recirculating damper. Installed hot water shut off to heaters.
Put a probe in the forward evaporator. With the engine fan on, temp drops just below freezing. 37f just before fan kicks on.
Lost some 134 checking the pressure and yes the temp dropped.

   

[iceman]

How are you checking pressure? When the system is off the you could lose a couple pounds of refrigerant almost to nothing before the pressure will drop. Pressures will stay at whatever ambient converts to on a pt chart. The best way to verify no leaks is with the system empty, fill it with dry nitrogen as that has minimal pressure temperature change and make sure the pressure doesn’t drop. If it does, find the leak with soap or introduce some refrigerant and use a leak sniffer. They actually work fairly well but should be used in a shop with minimal breeze. A system with a leak will be a never ending problem. Also, Fan cycling has mainly to do with High side pressures.

[smorgan87]

If the pressures r good and it blows cold then roll with it. If/when it gets low again. Id take icemans advice and test it that way.

[DosGatos]

(07-19-2018 )iceman Wrote:  How are you checking pressure? Fan cycling has mainly to do with High side pressures.

I'm running the ac with a gauge on the low side. From one day to the next, same ambient temp/ same pressure.
Understand fan cycling is driven by high pressure switch. Was just curious to see the evaporator temp change as the fan cooled the condenser. Wasn't sure if there is a target temp for the evaporator or do I rely on the low pressure thermistor to cycle the pump if it gets too cold. Still getting a sense of the thing.

[iceman]

Ok that’s a good sign. Really no exact target, the baseline numbers I gave will indicate a correct charge and clean evap and condensing coils, with good air flow across them. Not sure which system you have but when you say thermistor I’ll guesss it’s a thermostatic expansion valve (TXV). These have a capillary line with a bulb on the end that attaches to the outlet of the evaporator. The bulb has a cross charge of refrigerant in it so that when the outlet line of the evap coil gets cold, it closes the diaphram in the TXV thus reducing refrigerant flow and cooling capacity. This exact same thing happens if the low side coil is dirty- Low air flow does not let the refrigerant “grab” enough heat from your cab,thus lowering the temp of the refrigerant and causing the txv to pinch off. In a case like this no amount of adding refrigerant will help except to cause the compressor to shut off on high head pressure sooner. Most important thing is keep both coils clean for proper airflow and your system will work as intended.