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AC 101

Posted: Wed Jun 15, 2011 11:46 pm
by bromodragonfly
Saw the locked sticky and it bugged me. I'm not a journeyman HVAC guy (I'm serving an apprenticeship), but I can make a few corrections and hopefully contribute something to the forum. I've done some work on my 2.8L 1987, which pretty much included replacing everything except the evaporator and condenser coils... so I'm somewhat familiar with the system.

System components. In relative order.

Compressor: Some refer to it as a pump, but the sole purpose of the compressor it not to move refrigerant, but to compress it from a low pressure gas into a high pressure gas. The high pressure gas will be high in temperature, due to the heat of compression (your discharge lines should feel hot when the compressor is running). The compressor is belt driven, although the clutch to engage it is electrically activated.

Condenser: The high pressure and high temperature gas flows from the compressor into the condenser. The condenser is either part of your radiator (but separate from the engine cooling loop), or somewhere nearby, where it is going to get ample airflow. The air moving past the condenser will take away the heat from the refrigerant. It is converted from a superheated gas, to a saturated liquid, to a subcooled liquid. The pressure in the condenser is constant.

Orifice Tube: It basically creates a large pressure drop as the refrigerant prepares to enters the evaporator. This pressure drop enables the liquid refrigerant to boil. The boiling of refrigerant enables it to readily absorb heat from its surroundings.

*Some later models use a TX valve (thermostatic expansion valve) instead of an orifice. The purpose of the TXV is the same as the orifice, but a TXV is able to regulate the amount of liquid that it passes to the evaporator. Both will be installed BEFORE the evaporator. There is a bulb and capillary tube that contain a gas, which runs from the TXV to the outlet of the evaporator. The warmer the gas leaving the evaporator, the more 'open' the valve becomes. I have read that the evaporator core (and TXV) is contained within the dash, near the heating core, but have never had to work on mine myself. On my 87, the orifice tube is under the hood - there is a flange near the outlet of the evaporator which can be disassembled to give access to the orifice tube. Other vehicles have an orifice tube that looks like a "bulge" in the piping.*

Evaporator: Contains boiling refrigerant. Fans will direct air over the evaporator coils, and the boiling refrigerant will absorb the heat from that air. The now cold/cool air will be blown into the interior of your car. Refrigerant leaving the evaporator will be a low pressure, low temperature gas.

Suction Accumulator: A cylinder shaped vessel. Its primary purpose is to prevent any remaining liquid coming from the evaporator (hopefully there isn't any) from slugging into the compressor and causing damage. It gives any liquid from the evaporator the chance to boil off into a gas. The accumulator also contains a filter-drier, which will absorb any moisture and filter any debris.

Re: AC 101

Posted: Thu Jun 16, 2011 9:05 am
by 3X00-Modified
We need to also have someone verify what year the design changed so people know if they should be going after an orfice tube or TX Valve.