sigh, retard AC question.

nickademus · **Joined:** Mon May 09, 2011 2:15 pm **Posts:** 54

i cant get out to the jeep to look, since its on the road with someone else, otherwise i wouldnt ask.

http://www.jeepair.com/ac/2-8-liter-4-cylinder-diesel-358.php

which one is the low pressure switch, im pretty sure mine died.

Thanks as always guys.

geordi · **Posted:** Mon Aug 22, 2011 9:42 pm

The cheaper one. The more expensive one sits on the high-side tube, just next to the alternator body. The low side switch is on the drier canister by the firewall on the passenger side.

nickademus · **Joined:** Mon May 09, 2011 2:15 pm **Posts:** 54

cheers.

crackher · **Posted:** Tue Aug 23, 2011 12:30 pm

how do you know it is the low side?

geordi · **Posted:** Tue Aug 23, 2011 1:08 pm

Are you asking me?

I know b/c I have completely rebuilt my AC system due to that high-side tube breaking internally. The replacement came with the more expensive sensor.

The connectors on those two sensors are different. The high-side sensor has a round connector with 3 wires, the low-side is a 2-wire rounded-square connector with obvious flat sides.

In basic AC theory, the safety switch is located on the low side to cut off the compressor power when the low side pressure drops too low. The idea is that the compressor is sucking from the low side, and if there isn't enough gas left in the system to expand and maintain the pressure against that suction... The compressor will completely evacuate the low side, and damage itself. The safety switch is typically about a $15 part, they are all the same design - pressure above 20 psi, the power is connected.

Putting the safety switch (if there is only one) on the high side is not practical, as the compressor can make high pressure with very little gas in the system. Once it is compressed, it flashes to a liquid and cannot be compressed anymore. Thus, the pressure increases rapidly unless there is a vent somewhere - the orifice tube back to the low side. On our CRD, the more expensive sensor is on the high side as a max pressure safety. It probably relates to the operation of the electric fan to cool the system and reduce the head pressure, because both the high and low pressures vary with outside air temperature.

geordi · **Posted:** Tue Aug 23, 2011 1:11 pm

Also, you can know for certain which is which by clicking on the description link under the images on that page - Both items have a full (and very good!) description not only of what they are, but what they DO, and where they install.

That's a good site to have stuff like that!

sigh, retard AC question.

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