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Rawknees'Turbo Rawknees'Turbo is offline
Mighty Meatlocker Turbo
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Join Date: Apr 2016
Location: North TexASS
Posts: 10,461
A/C charging - vent temperatures and pressured method.

- If you have a suitable scale, weigh the cylinder and record the number in ounces. Weight doesn't mean much when converting from R12 to R134a and newly charging a now modified system, but it is nice to record how much refrigerant you added so to have a reference for future work (good advice from Charlie Griffith - the a/c big baller).

*** NOTE - run the engine for the last 20 mins or so of the vac procedure to allow some heat to build up - charging works better that way.

- following vac procedure from previous post, close manifold valves (leave service port valves open), shut off vac pump, disconnect yellow hose from pump and attach it to refrigerant tank's tap (tap closed, obviously).

* Note - you will leave the highside manifold valve closed from this point on - do not open it at all.

- purge yellow hose and manifold of air . . . remove brass cover from purge valve (located just above yellow hose fitting), open tap on refrigerant tank, depress the Shrader valve in the purge port for a few seconds (like 2-3) - gas will rush out and remove air along with it.

- statically fill system (engine off) . . . can upright (gas charging method), tank tap turned on/open, open manifold low side valve (both service port valves still open) . . . notice that pressure within the tank, and vacuum in a/c system, will cause refrigerant to rush into the system. Allow this to continue until the pressures stop increasing on their own. TIP - if you warm the tank with a space heater, heating pad, etc., more static charge can be accomplished.

- Place a large fan at the nose of the car and aim it rearword (helps prevent heat from building up under the car).

- Cabin windows up, doors closed, and engine lid open (do not need to charge with engine lid closed since you have a fan installed on the tail condenser) start engine, turn thermostat and blower fan settings to max and check to see if the compressor clutch is now engaged (if the static charge overcame the low pressure switch that's now in your system). If clutch not engaged, you will either have to continue with static charge using heat, or jumper the low pressure switch. Also check to make sure that all system fans are running, etc.

*** NOTE - many times you will see charging instructions that call for having the windows/doors open, but I was taught long ago that why charge the system that way when it won't be operated in that manner (aka - set up the system as you intend it to be used) - works for me, and is also Charlie Griffiths's approach, so a pretty good validation right there!

- With engine at idle speed, and clutch engaged, monitor high and low side pressures, and vent temperatures. The goal here is to find what are the lowest vent temps achievable within the lowest acceptable pressure ranges. For example, with your system, you will likely be able to get into the high 30s (if not even better), with highside pressure of about 220-240 and lowsider pressure of 28-33 depending on the outside temperature (high outside temps mean higher system pressures.) Don't pay much attention to the common pressure charts you see online - they almost all advise pressures that are too high for maximum performance - shoot for the numbers I posted if you have temps there in the mid-upper 80s or above (slightly lower numbers if outside temps are lower).

NOTE - you must periodically close the lowside manifold valve in order to check actual system pressures during charging - much higher numbers are seen with the tap open and the tank connected.

*** Obviously, this is all going to take some patience and experimentation on your part - if you "overcharge" and vent temps rise (which is what happens), don't be afraid to let some gas back out. You do this by turning the clutch off and depressing the purge valve on the manifold set (the tap on the refrigerant tank must be turned off when you do that). Do not push that valve with the clutch on or outside air will be sucked into the system and you basically have to start over with the process.

- When satisfied with pressures and vent temperatures, close lowside manifold valve and close refrigerant tank tap (leave service port valves open), and observe gauges with the system running. Are the pressures pretty consistent? Are the needles stable and not vibrating or bouncing around (a sign of air and moisture in system if bouncing)? If looks good, then close service port valves, re-open manifold valves and purge manifold and hoses of trapped refrigerant by using the purge valve. Once purged, all hoses can be disconnected.

- Weigh refrigerant tank and record how much you put in the system.

- Check for leaks at all fittings by using the tried and true, soapy water method . . . some water with a little dish soap mixed in applied to fittings with a paint brush. Any leaks cause tons of bubbles to form - just like checking for natural gas leaks.

Last edited by Rawknees'Turbo; 09-19-2017 at 08:23 PM..
Old 05-26-2017, 10:31 AM
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