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HoustonPhotog
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 Posted: Tue Sep 10, 2013 1:44 pm Post subject: How Much Refrigerant for 87 Westy - 134a? |
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I had my AC system overhauled in my 87 Westy. New Sanden compressor, new drier, new expansion valve.
The AC currently cycles a lot. It kicks on, it cools then a minute or two later it shuts off and blow warm air. Then in a few minutes the compressor will kick back on and cool for another couple of minutes before shutting off again.
My VW mechanic thinks the compressor is at fault and is not working.
Although I have read here that overfilling the system with refrigerant could also cause the system to act like this.
I recall him saying he added charged the system with "like 3lbs of refrigerant" when he first did the install. Im wondering if he put the required amount for an R12 system in this R134A system instead.
Ive also noticed that the R134A would require considerably less quantity of refrigerant than filling it with R12.
Anyways... Any info is greatly appreciated.
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dhaavers
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| Posted: Tue Sep 10, 2013 8:04 pm Post subject: |
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Original spec for R-12:
Air & Water-cooled = 45oz (~2.8 lbs)
Diesel 1986 & newer = 50.75oz (~3.1 lbs)
I believe 134a requires about 15% to 20% LESS refrigerant by weight.
Exact amount is determined by balancing system pressure while charging
and accounting for ambient temp & pressure (ie: altitude, if extreme).
Please remind your tech that this is an R-12 system, probably converted
to 134a in the second decade of it's life. Consider the source of his "specs".
Overfilling could cause short-cycling & shorten the life of your new
compressor. Have him adjust & then look for a new shop (or DIY)...
Or your pressure switch(es) could be wonky... 
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Pchill2
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| Posted: Fri Feb 10, 2023 9:22 am Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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The R134 changeover TSB says 47.6 oz of R134 in the Vanagon.
http://www.gti16v.com/tb879503.htm
Can anyone confirm this amount is correct?
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vanis13
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| Posted: Fri Feb 10, 2023 10:41 am Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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It ultimately depends of setup of system - hose diameter, routing, compressor size, etc.
The link you provided is close but different than other Vanagon R134 conversion docs.
Many different approaches to getting it just right one being fill until cooling isn't getting any better (if it gets worse, suck some back out).. This takes temperature readings and patience.
That said, the 47.6 is 3.966 12 ox cans. It seems mine take right around 3.75 cans to get to a good place.
Bigger issue may be inadequate drying (vacuum) leaving moisture in the system.
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Pchill2
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| Posted: Fri Feb 10, 2023 10:52 am Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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Much appreciated.
All the lines have been open for almost a year but will be replaced with Aeroquip R134 lines. I have a new (still sealed) drier I plan on installing just before I put it under vacuum.
Can you use argon to purge the air out of the system prior to vacuum?
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vanis13
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Pchill2
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| Posted: Fri Feb 10, 2023 11:41 am Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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khughes
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| Posted: Fri Feb 10, 2023 1:58 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| vanis13 wrote: |
| If you were at higher altitude than GA boiling point of water even at vacuum would be an issue which would need a 3x vacuum/nitrogen purge. |
The altitude has no effect on the boiling point of water in a *sealed* system like an A/C system. Water at 1mbar inside the system with 1000mbar outside the system is the same as water at 1mbar inside the system with 700mbar outside the system.
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vanis13
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| Posted: Fri Feb 10, 2023 3:15 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| khughes wrote: |
| vanis13 wrote: |
| If you were at higher altitude than GA boiling point of water even at vacuum would be an issue which would need a 3x vacuum/nitrogen purge. |
The altitude has no effect on the boiling point of water in a *sealed* system like an A/C system. Water at 1mbar inside the system with 1000mbar outside the system is the same as water at 1mbar inside the system with 700mbar outside the system. |
That would be true IF one could draw a perfect 29.92 inHg vacuum at any altitude...But since higher altitudes only allow for lower vacuum the evaporation of water happens at a higher ambient temperature....where the whole AC system is in the engine bay the solution is to run the engine to get underhood temps high enough. with the Vanagon system so much of the system is not in the engine bay - all the hoses to the front and the condenser on the other side of the heat-generating engine - one can't get the system hot enough....There a discussion and table on this in the hard-copy AC book I have (which I don't have access to right now)
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djkeev
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| Posted: Fri Feb 10, 2023 3:23 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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Here is an old post with a quantity exchange chart in it......
| cellerdoor wrote: |
Finished installing all of the rest of my winter upgrades and put the battery back in. Always very nervous when I hit that starter for the first time after 5 months of hibernation. Once again she started right up and all of my new devices work as they should (stereo, ignition switch, belts, etc).
I unplugged my compressor since its not charged yet but was able to test out the evap. fan. Everything running quietly.
I've been reviewing vacuum pump and gauge sets and have been looking on craigslist to see if a quality unit came up for sale, but no dice. Ended up buying some Mastercool equipment since that manufacturer seems to be a good fit for limited occasional use and should resell for a decent dollar should I decide to get out of the AC business.
Vacuum pump is Mastercool 90062-A single stage deep vacuum rated at 75 microns. Dual stage would be better but at double the price I didn't see the real benefit. Should pull the system down to boil off any moisture. $100.
Manifold Gauge set is Mastercool 66773 which is a good basic set $80.
I'm going to order my redtek on Monday and should need three cans. From the redtek site and Bentley showing a need for 50.75 ounces of R12:
When I order I need to determine if I need any additional products. Since I have all new components I'm going to skip the sealants and have already placed the required compressor oil and other component oil in the system (around 8 oz, all PAG 46) but don't know if I need the "Line Charge" in addition to this.
I also need to get the required adaptors for the charge lines. Since I mounted my compressor sort of sideways I need 90 degree quick connectors for clearance, but want to get my gauge set in my hands first. I also need to get something to measure duct air temp.
Equipment coming in a week, in the mean time I'm going to re-study charging procedures. |
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djkeev
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Pchill2
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| Posted: Fri Feb 10, 2023 3:47 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| djkeev wrote: |
There are oil type and quantity concerns also when swapping refrigerants.
Most reports are that 134a dies not cool as well as r12 or r12a.
Dave |
Can you run redtek in an R134 compressor?
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djkeev
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khughes
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| Posted: Fri Feb 10, 2023 4:02 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| vanis13 wrote: |
| khughes wrote: |
| vanis13 wrote: |
| If you were at higher altitude than GA boiling point of water even at vacuum would be an issue which would need a 3x vacuum/nitrogen purge. |
The altitude has no effect on the boiling point of water in a *sealed* system like an A/C system. Water at 1mbar inside the system with 1000mbar outside the system is the same as water at 1mbar inside the system with 700mbar outside the system. |
That would be true IF one could draw a perfect 29.92 inHg vacuum at any altitude...But since higher altitudes only allow for lower vacuum the evaporation of water happens at a higher ambient temperature....where the whole AC system is in the engine bay the solution is to run the engine to get underhood temps high enough. with the Vanagon system so much of the system is not in the engine bay - all the hoses to the front and the condenser on the other side of the heat-generating engine - one can't get the system hot enough....There a discussion and table on this in the hard-copy AC book I have (which I don't have access to right now) |
If you are meaning to say that the efficiency of the vacuum pump decreases at higher altitudes, causing the ultimate vacuum level to be impacted, that's a different situation. No matter where the components are installed, engine bay or elsewhere, it's hermetically sealed and totally isolated from atmospheric pressure, so altitude has no effect. Obviously the hotter the system the easier it is to evaporate the moisture, but there's no *necessary* correlation between altitude and temperature. If you have a source for your contention I'd like to read it, 'cause I don't see how it comports with physics.
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vanis13
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| Posted: Fri Feb 10, 2023 4:10 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| khughes wrote: |
| vanis13 wrote: |
| khughes wrote: |
| vanis13 wrote: |
| If you were at higher altitude than GA boiling point of water even at vacuum would be an issue which would need a 3x vacuum/nitrogen purge. |
The altitude has no effect on the boiling point of water in a *sealed* system like an A/C system. Water at 1mbar inside the system with 1000mbar outside the system is the same as water at 1mbar inside the system with 700mbar outside the system. |
That would be true IF one could draw a perfect 29.92 inHg vacuum at any altitude...But since higher altitudes only allow for lower vacuum the evaporation of water happens at a higher ambient temperature....where the whole AC system is in the engine bay the solution is to run the engine to get underhood temps high enough. with the Vanagon system so much of the system is not in the engine bay - all the hoses to the front and the condenser on the other side of the heat-generating engine - one can't get the system hot enough....There a discussion and table on this in the hard-copy AC book I have (which I don't have access to right now) |
If you are meaning to say that the efficiency of the vacuum pump decreases at higher altitudes, causing the ultimate vacuum level to be impacted, that's a different situation. No matter where the components are installed, engine bay or elsewhere, it's hermetically sealed and totally isolated from atmospheric pressure, so altitude has no effect. Obviously the hotter the system the easier it is to evaporate the moisture, but there's no *necessary* correlation between altitude and temperature. If you have a source for your contention I'd like to read it, 'cause I don't see how it comports with physics. |
When I find it I'll post it...the kink in your description may be that the vacuum pump one uses at altitude is working at the altitude not in the closed system...Once the system is closed, I would agree that altitude doesn't make a difference (unless the container changes volume - think square soda bottle expanding to round)
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djkeev
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khughes
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| Posted: Fri Feb 10, 2023 6:13 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| djkeev wrote: |
He is talking about pulling the initial vacuum before charging.
Vacuum readings at altitude change. |
Vacuum *gauge* readings change at altitude for sure. That has nothing to do with vapor removal however. At 7K ft elevation, you only have 23.09"Hg pressure to work with. But if the gauge is re-zeroed at local station pressure, and the system is evacuated to a gauge reading of 23.09"Hg, the pressure in the system is exactly the same as with gauge pressure of 29.92"Hg at sea level. Liquid evaporates the same in both systems, irrespective of the external atmospheric pressure.
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Abscate
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| Posted: Fri Feb 10, 2023 7:13 pm Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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| Quote: |
| But since higher altitudes only allow for lower vacuum the evaporation of water happens at a higher ambient temperature. |
Ooof. Nope.
Vacuuming purges air from the system much better than a flush gas. You want to pump on it for an hour, minimum , to desorb moisture from all the surfaces , too. You can test it by seeing if it holds vacuum overnight. Not a totally reliable test but works 95% of the time and always for. If leaks , like a rolled o-ring or forgetting to tighten the office tube union. Yeah, I done that.
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MarkWard
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| Posted: Sat Feb 11, 2023 6:26 am Post subject: Re: How Much Refrigerant for 87 Westy - 134a? |
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My advice would be to charge the AC system monitoring gauge pressures and vent temp. Not a predetermined amount.
I recall the a/c evaporator core temp cycles the compressor to keep the evaporator from icing up. There is also a high pressure compressor cut out switch. There is also a low pressure compressor cut out switch.
I revamped a 90 camper with factory air including a new dual pass condenser and charged with 134. Charged as I described above. Cools fine. Pay attention to the gauges when the compressor cycles. That should indicate which feature is cycling the compressor. I doubt the problem is the compressor, but a testlight or volt meter on the compressor clutch power lead will tell you if the compressor clutch magnet is the cause. If you have power at the compressor and the compressor clutch is not engaged, that would indicate a compressor fault. Otherwise it is being commanded to shut off.
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