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Orifice tube recommendation

TransAm525 on Thu January 05, 2012 6:01 AM User is offline

Year: 1978
Make: Pontiac
Model: SE Trans Am
Engine Size: 400
Refrigerant Type: 134a
Country of Origin: United States

Hi everyone. I'm new to the forum, but a frequent visitor to the site. I've finally decided to re-install the a/c system back into my 1978 Trans Am since first removed during the initial restoration. The full setup is listed below for your reference in response to my question. I need an orifice tube recommendation based on my system. The vehicle is driven in California (dry climate). Daily driving, the engine operates around 2000 rpm on the local area roads and 2700-3000 rpm on the highway. The crankshaft pulley is a March underdriven part, with a 17% underdrive, so the compressor will be running slightly slower than if installed on a purely stock engine.

- Vintage Air Sanden 508 compressor
- Parallel flow aluminum condenser (15.5 x 30.5)
- Aeroquip AC braided stainless AN-8 high side line and fittings (with charge port)
- Aeroquip AC braided stainless AN-10 low-side line and fittings (with charge port)
- New liquid return line
- New R-134a specific binary switch
- New GM evaporator core
- New receiver/drier and J-tube
- New thermal switch
- New blower motor relay
- New heater resistor
- New GM blower motor and fan wheel

Every single AC and heater related component inside the vehicle has either been replaced or refurbished. The system will run R-134a. The radiator has two 1,650 cfm electric puller fans mounted for engine cooling (no engine mechanical fan), serving to pull air through the condenser as well when stopped. Additionally, one of the fans will be wired to automatically to start when AC is selected, with the other (or both if AC off) delayed until 170° engine coolant temperature is achieved. With the given setup, what orifice tube would you recommend to provide optimum interior cooling? I am also interested in any compressor oil recommendations you may have.

TRB on Thu January 05, 2012 10:52 PM User is offlineView users profile

With that large of PF condenser I would stay with the OEM OT. As for oil, Sanden with come with close to 6 ounces. That should be close but with large evap core might add an extra ounce at the most.


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mk378 on Fri January 06, 2012 12:12 AM User is offline

Don't get fancy with the fans. You are going to need all the fan you can get-- both running at the same time with A/C on. Pressure switches on the high side are sometimes used to shut down electric fans when not needed (cold weather and/or the car is moving).

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