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Freightliner A/C diagnosis
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Jon Hagen
Posted 6/7/2008 15:32 (#392467 - in reply to #392438)
Subject: RE: Freightliner A/C diagnosis

Hagen Brothers farms,Goodrich ND
almarti1 - 6/8/2008 13:41

I then got in the bunk and heard a hissing noise where the compressor/condenser (not sure which) is located. The hissing noise occurred every 30 sec or so which leads me to believe it has something to do with the loss of pressure. What is the problem here...possible solutions? TIA

I reread your post and what you hear in the bunk is the refrigerant gas expanding in the evaporator, this is normal, but may also be where your leak is if you have one.
Get a set of both low and high side gauges on there and try adding more refrigerant, as with only 30-45 psi in there with the compressor off , you have no liquid refrigerant in there only a little gas. normal charge with the compressor off should read at least 75 psi on both sides with liquid refrigerant in the system.

Add more and read pressures only when the compressor is running.
With a proper charge, you should have 28-30 psi on the low side and 125 or more psi on the high side. The high side pressure depends on air temp, the warmer it is, the higher the high side pressure will go.

I like to charge by vent temp, with a vent thermometer in an ac vent.
Add enough refrigerant to get the system working, then slowly add refrigerant a few ounces at a time until adding a little no longer lowers the vent temp. Stop there, that is the sweet spot that will give max cooling with minimum high side pressure.
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