AC Recharge

[Venturer]

Sorry Ivan, my cans were 12 oz and not 16, so 48 oz added. After 30-40 minutes, the low pressure is up to 40 and the high is down to 75. Am I correct is assuming they will equalize when the compressor is not running??  

[Ivan K]

I'd just go by the high pressure readings to tune it up. 4lbs/64oz is just a ballpark. He static pressures will equalize in time. If they did not, it would indicate some sort of obstruction but they are moving so should be good.

[Venturer]

Thanks. I'll pick up another few cans tomorrow and top it off. We only have a few trips planned this summer before we go back to Havasu in Oct.  If any leak becomes bothersome, I'll just rely on the generator and roof Air and have the shop there locate the leak. 

[cbr046]

30F differential is fantastic.  I wouldn't add any more.  4 cans / 48 Oz is about all the system will hold - mine holds 52 oz total.  @jacwjames posted a chart of temp vs hi & low pressures.  Mine was 124 / 24 at 66F when I got it back from the shop. 

Too much freon and you could be crying all the way to the bank.  Too little freon and you might sweat a little - Take your gauges and freon with you this summer.

Just MHO

- bob

[Happycarz]

My 2¢ worth. I haven’t seen it mentioned so I am just verifying:

1.) You have a huge fan blowing on the condenser. The bigger the better. Use what you have, on high speed.

2.) You have the engine running on high idle, at 1200RPM.

[Venturer]

I do not have a fan blowing on the condenser

I have been charging it on high idle @1000 rpm. Tomorrow, if needed, I will top it off @ 1200 rpm.

Edited May 11 by Venturer

[CAT Stephen]

@Venturer (Doug),

 

Your understanding is correct that your high side and low side will eventually equalize.  The equalization can take up to 12 hours in some cases and less than 10 minutes in other cases.  These static pressures (i.e. pressures when the system is not running) are not useful except when both sides are at zero pressure.

Here is the official R134a universal Pressure / Temperature chart to use when charging your dash AC:

• 

Here are key procedures for you to follow when charging your AC properly:

- Before starting the recharge process,

• Insure that you have quick access to a minimum of ~ 5 gallons of hot water from your RV or home water heater. This water should be ~120F-140F.  
• All automotive and truck/bus dash based HVAC systems are checked and charged at engine idle speed.  Thus, there is no need for high idle. 

- Don't attempt to charge your system below 75F degrees as it is much more time consuming due compressor frequently cycling on and off  which makes it difficult to stabilize systems pressures.  

- Set your dash AC to "Max"

- Set your dash AC temperature to the coldest setting

- Check your pressures only after your compressor has engaged for 15-20 seconds to give ample time for the high and low pressures to stabilize

- Start adding R134a refrigerant SLOWLY while watching your low pressure gage, keeping the can upright to prevent the compressor from ingesting liquid refrigerant ONLY when the compressor is running.  You will notice an initial spike in pressure on the low side which will begin to trail off as the refrigerant is transferred from the canister.  When the spike decreases significantly, lower the refrigerant canister into the hot water.

• NEVER risk destroying your compressor by turning the can upside down as that WILL inject liquid refrigerant on the low side which may, in some cases result in AC compressor destruction.  Take heed of the warning from @cbr046 and I.
• While adding refrigerant, lower the refrigerant can into the hot water mentioned earlier to help the remaining refrigerant vaporize while the canister is upright.  Be prepared to change out your hot water 2-3 times per canister to completely evacuate all remaining refrigerant from the canister

Please share your pressure differentials and ambient (outdoor) temperature in this thread.  If they are vastly outside the ranges (i.e. 80F ambient temperature with 25 PSI Low and 200 PSI High), there are other issues in your system.  What is common with diesel pushers is some variation from the standard R134A P/T charts due to the vast lengths of the refrigerant lines between the engine's AC compressor and the dash evaporator.

As @cbr046 also mentioned, a 30F differential between ambient and you dash air output is excellent.   

 

Edited May 11 by CAT Stephen

[Venturer]

I'm probably going to put my AC project on hold till the OAT gets up into the upper 70's which will be awhile. I have 48 oz into the system, however, over night the high and low pressures are lower than yesterday. I either have a substantial leak or the colder temp is affecting it. Warmer temps will help.  

[trailmug]

If the system sat overnight, your system pressure on both sides should be nearly equal to the vapor pressure at your ambient temperature (the R134a temperatures listed on the face of your gauge set). Resting pressure is hugely dependent on ambient temp. 👍

If the gauges read lower, the leak is bad enough that you have no liquid left in the system and the leak is enormous and shouldn't be that difficult to find. Barrier hoses have a solid nylon core so they really don't tend to develop leaks. 

Edited May 11 by trailmug

[Venturer]

When I checked on it this morning, the pressures were equal at around 65 psi which to me, indicates no major leak. When engine started and AC engaged, the high settled near 75 but the low was below 10. The OAT was near 50 degrees. It's supposed to be 77 tomorrow and will check it then.  

[trailmug]

With an ambient temperature around 66 F, that makes sense, but the engine running pressures sound low.

[CAT Stephen]

11 hours ago, Venturer said:

When I checked on it this morning, the pressures were equal at around 65 psi which to me, indicates no major leak. When engine started and AC engaged, the high settled near 75 but the low was below 10. The OAT was near 50 degrees. It's supposed to be 77 tomorrow and will check it then.  

@Venturer,

Thanks for the pressure and ambient temperature report Doug.  Now the troubleshooting begins:

• Recharge your system with one (1) can of UV Dye then add R134a refrigerant
  • https://www.amazon.com/ZeroR-Leak-Detector-R134_-R12_/dp/B08BQFXNZ8/ref=sr_1_7?dib=eyJ2IjoiMSJ9.8pxgDbr3uxRBd8-rKi1j6bQouIp1DV9f4zQEhMhjgkuRvZcvbNM0xcZ1JpRjYVBuUkgElUEl3Klpr93dyA6hUreBTA2ObdbugcMLIV_1LcXQCHFsTpQKAYtrvQzKFV5SuIYdbXwst2YvXn65EZrFSL6mIZPFa2qdOzv536gYEKFj3hvsoNWNPI3uFtEwy8gQymWXoqYitTSYjPGnXuCg1SBdd4U-FlUUpr0ehhpWXq9c19Q1T6T7Hwuq5SoQ-N6bZkOd3vzhXGNPOQlhPMPP_QURQvL34npYySKfeBBuf3U.5oxoepYgVR84dyOFG6vpRtljRtbqK11XfHpiH-TGtCY&dib_tag=se&keywords=r134a+with+dye&qid=1715483320&sr=8-7
  • Run your Dash AC for ~15 minutes to thoroughly disperse the UV dye throughout your dash AC system:
  • Thoroughly clean your schrader valves that you just used to refill your system with refrigerant so that they have no visible UV dye using your UV Blacklight kit and goggles specifically for  illuminating UV dye:
    • https://www.amazon.com/Uview-413010-Battery-Powered-Detection/dp/B000NBWCFC
• Wait until it is dark outside for a minimum of 24 hours since you refilled your system with UV dye refrigerant specified above
• Using a UV Blacklight kit and goggles specified in the previous link, inspect the following components for UV dye which indicates leaks:
  • Every schrader valve in your entire dash air system.  Most coaches have a minimum of four schrader valves for refilling at both the coach rear and the coach front
    • My coach has eight (8) schrader valves for the dash HVAC system (leakapooloza)
  • Every fitting in your your entire dash air system such as the inlet and outlet of your AC filter, the inlet and outlet of your AC compressor, and the inlet and outlet of your dash evaporator (if the evaporator fittings are accessible without substantial disassembly)
    • 80% of coach dash air refrigerant leaks are due to faulty schrader valves.  These valves are infamous for leak failures.
    • Don't be concerned that you can't see / check the full length of the refrigerant lines running from the front to the rear of your coach as they are typically inaccessible and typically have no fittings except at each end of your coach
    • If you CAN'T find any refrigerant leaks through the inspection of the above components, proceed with the task of disassembly to access and view your dash evaporator and its inlet and outlet fittings

Edited May 12 by CAT Stephen

[Venturer]

The OAT has reached 77 degrees, so I gave it another try. Standing pressures were 65 on both high and low. Once started, the high went to 125 and the low was at 15. I added most of another 12oz can for a total of 58-60 oz. The high came to 155, but the low is still around 15. I'm going to stop with it here. With the OAT @77, the vent temp is 43 for a 34-degree drop. That's good enough for me regardless of the pressures so I'm stopping here. I would think the pressures would be higher with a new compressor, but being new today doesn't guarantee it's working as designed.  I know what I 've done is only a temporary fix, as any leak is still there. If it doesn't leak when not in use, I'll check and add if necessary when we need the cooling. Until we get back to AZ in Oct, I can use the generator and roof air if necessary. Thanks to all who offered suggestions. I'm a little more informed now than I was a few days ago. Owning an older Monaco is like going to school again, except I have more teachers. 🙂 

[trailmug]

👍 keep in mind if it happens to leak down to atmospheric (say 4PSI or less), as Vito mentioned, you're gonna be exchanging air and moisture into the system. A little air is mainly an efficiency/capacity hit, but moisture is a sworn enemy. PAG oil is hygroscopic and as far as I know, can't be dried with a vacuum pump. Moisture + refrigerant + heat makes hydrofluoric acid, which eats compressors and coils.

[Venturer]

6 hours after topping it off, both gauges have settled @78 psi with 82 degrees ambient. I'll check over the next few days without starting it to see what I have. It supposed to be cooler, so I expect the numbers to be slightly lower too.  

[cbr046]

On 5/11/2024 at 9:30 AM, CAT Stephen said:

• 

What is common with diesel pushers is some variation from the standard R134A P/T charts due to the vast lengths of the refrigerant lines between the engine's AC compressor and the dash evaporator.

When I got the RV back from the shop the ambient / static pressure was perfect - 66F and 66 psi on both high and low sides.  The compressor had been off for hours.  When I engaged the compressor the high and low pressures were low according to the chart - 124 / 19 at 1200 RPM.  or very low 103 / 24 at 600 RPM

So I started thinking about this . . . . There's a LOT of volume in those lines, much more than an auto (which almost every website is targeting).  Adding more freon (and more and more freon) will get pressures in range but now there's A LOT MORE FREON in the system, which (in my case) was a very bad thing.  Expensive, too.  I suspect the static or equalized pressure would now be out of range with the corresponding temperature. 

But on the other hand . . . . I had just gotten home so the freon in those long lines was probably 5-10F higher (on average front to back) than ambient temp, being up high in the chassis bays and heated by the engine, so that might skew the static charts.  Still, "they said" they put in the right amount of freon per a sticker somewhere (52 oz), which I've never run across.  They may have added freon by volume and not by pressure.

I haven't had a chance to compare intake and discharge air temps but I was cool enough driving home out of FL yesterday (Max AC, fan on high, blowing on me).  Until it "just quits" I'm rolling with it . . . . and when it does quit I'll add just enough.

Thoughts?

- bob

 

[Venturer]

Today, 30 hours later, I have 70 and 70 @ 72 degrees. I'm not going to start it for a few days to see is the leak is only at running pressure. Like Bob, I also have lower running pressures when I know the system had to be full.  

[Venturer]

After checking the static pressures for four days, the values seem to be 4-5 psi below the ambient temperature. A 52-degree morning saw 50 psi static. Later in the day 67degrees saw 62 psi. I think this means I do not have a serious leak when not running. The temp should get to 80 on Saturday. I'll start it up then and see how much temperature drop I get. In the back of my mind, I'm suspecting my new compressor might be the culprit. It couldn't build to the expected pressure after I had close to 60 oz in the system even though it was bringing the temp down 33 degrees.  

[CAT Stephen]

17 hours ago, Venturer said:

After checking the static pressures for four days, the values seem to be 4-5 psi below the ambient temperature. A 52-degree morning saw 50 psi static. Later in the day 67degrees saw 62 psi. I think this means I do not have a serious leak when not running. The temp should get to 80 on Saturday. I'll start it up then and see how much temperature drop I get. In the back of my mind, I'm suspecting my new compressor might be the culprit. It couldn't build to the expected pressure after I had close to 60 oz in the system even though it was bringing the temp down 33 degrees.  

Doug,

 

What is key is that your system is yielding a 33 degree temperature drop which is good and means that your compressor is currently sufficient.  Using static pressure to troubleshoot or to reveal leaks is inconclusive.  Inject the UV dye that I specified above into your system and follow the procedure to reveal leaks.

[Venturer]

7 hours ago, CAT Stephen said:

Doug,

 

What is key is that your system is yielding a 33 degree temperature drop which is good and means that your compressor is currently sufficient.  Using static pressure to troubleshoot or to reveal leaks is inconclusive.  Inject the UV dye that I specified above into your system and follow the procedure to reveal leaks.

That sounds like my next step. Need to gather some items and find the time to search further. Thanks for the help.