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Old 08-27-2011, 05:59 AM
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Any AC experts around? Big problem...

I have a 97 F 350 CC. I have installed the 4th compressor and now have confirmed everything is good except the low side will not pull down.

This truck used to be the coldest one I had and then just all of a sudden got just okay cooling this spring. I have installed 4 different compressors from 3 different companies. The last one being a factory Ford one. 2 accumilators and 3 orfice tubes. The condessor and evaporator has been flushed and tested. Vaced it way down for a long time and recharged last night after the Ford compressor install. It is getting 20* of subcooling accross the condesor and the evap is working correctly. There is a 4* difference in the vent temp to the coil temp so that is good.

The only thing that is not perfect is that with the correct amount of charge in the sysytem the low side is not pulling down like it should. This is what has caused me to install so many different compressors because my AC friend was saying the compressor is weak. The low side will not pull down below 54. The high side is right at 200 in about 90 degree ambient.

The orfice tube is the red one but is from Oreilly's. Is it possible that the orfice tube is not working correctly and the ones from Oreilly's are not up to spec? I am thinking of getting one from the dealer and going through the whole process of breaking the system apart again. I have dropped about 1000 bucks on this so far trying to get it really cold again and do not want to waste any more money.

So looking to see if anyone has had this experience before. Please help... Thanks
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Old 08-27-2011, 11:03 AM
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Thats weird JJ
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Old 08-28-2011, 06:31 AM
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I have about 500 bucks in my AC system, and thats with a shop doing the work. Some things are best left to a shop. new seals, accumulator, sensors, and compressor.

However, that is strange. And yes, sometimes aftermarket companies sell inferior seals and such, so its possible that its the wrong orfice tube.

But your saying it wont take a full charge? Also, R134a works on weight, not pressure. If a refrigerant system calls for 2 oz's of refridgerant, then thats all it should take, add too much more and your going to blow the system. Also, the truck needs to be completely COLD when doing it. Let the truck sit for a few hours and cool off if your driving it.

AC is a bastard, and as mechanically inclined as I am, I wont touch one.
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Old 09-21-2011, 08:33 AM
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I purchased a 97 7.3L F350 Turbo crew cab which does everything well but blow enough cold ac. I had a shop test it and recharge it. It blows cold enough to cool the front seats but the passengers in the back seats don't feel a thing. Is this normal in these older trucks?

I can't imagine that it is but I thought i would ask in case the if anyone else has had similar experiences. Thanks
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Old 10-06-2011, 09:18 AM
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Do you have a intercooler? Is it possible you pinched a hard line coming from the evaporator to the compressor getting it around the boost tubes?
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Old 10-08-2011, 08:14 AM
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A restriction after the low side pressure tap, over charge, high load on the system or oversized orifice. Check the superheat of the evaporator not sure on a vehicle but you probably don't want much higher than 15*. What's the discharge air temp? Did you weigh in the charge?
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Old 10-08-2011, 08:21 AM
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Where it the lowside test port? +1 for restriction in lowside line or overcharge.
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Old 10-08-2011, 10:14 AM
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The low side test port would be the service port on the larger tube I'm probably just using a different term than you've heard. Typically if you have a restriction on the low side you will see low pressure at the low side gauge but if it were after the gauge you would see high pressure there could be some sort of strainer/filter dryer just before the compressor blocked causing something like this.
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Old 10-09-2011, 06:51 PM
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99% of the time i see dust, dirt, hair ect ect Blocking the evap channels and causing the evap to turn to a block of ice real quick which causes the compressor to cycle making it seem like a low charge and like there is nothing blowing out of the vents.
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Old 10-10-2011, 03:12 PM
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He said he's seeing high back pressure not low
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