A/C techs, Need Help

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by TurnAndBurn, Jun 4, 2020.

  1. TurnAndBurn

    TurnAndBurn Bobtail Member

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    I have a 99 379 EXHD 3406E 63" sleeper. The AC used to blow ice cold for 3 or 4 years without issues. Chain of events. We hit a deer, body shop puts in new condenser and dryer. A few months later it's low on freon. Found a leaky Schrader valve, and replaced. Gets low on freon again and the compressor locks up. I bought and installed a new compressor. At that time I also found it's leaking around the low pressure switch, I ended up replacing the switch and oring. I also added some oil to the system. from that point on the air conditioner has never worked well. A year later it's still holding pressure and it seems like all the leaks have been found, but it does not cool well at all. Took it to our local diesel mechanic who is a very knowledgeable reputable truck mechanic. He pulled the orifice tube and found aluminum shavings on it. He said it should have been flushed after the compressor locked up, which I should have thought of that and dropped the ball there. So he figured it would be best to flush the lines and condenser, install a new orifice tube, dryer, and compressor in case any shavings made it to it. After doing all this the pressures seem pretty normal, and the fan kicks in and out with high side pressure like it should, but the coldest it will get is around 65° with just the cab on and idling at a thousand rpm, and 68° with cab and bunk on at a thousand rpm. It has that musty feeling as well. The cab and bunk both are the same temps. He filled it with 5 lb and has a brand new snap-on AC machine. It's been evacuated and filled four times in the last week. He also tried overfilling it one of those times just to see if it made any changes and it did not. The heater core is shut off, and the blend door is closing all the way. I'm almost at the point I just throwing parts at it but it's a pain having to evacuate and refill every time. Have considered new high side lines and condenser. Possibly even evaporator. But this was all working great before the compressor locked up and I installed the new one and added some oil it's never been the same. He did blow oil out of the lines when he flushed it and then reinstalled the new compressor, dryer, and orifice tube. Is there a separate orifice tube for the rear bunk something I just thought of and was wondering myself? I would still think if there was and it was plugged, the front would work well since it is new. Any help is appreciated, thanks.
     
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  3. Rideandrepair

    Rideandrepair Road Train Member

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    It’s impossible to fully flush the condenser and evaporators, once they’re contaminated. Because neither is usually a closed loop. I flushed my evaporators quite a bit, they never did run clear. I wish I would have changed them, since I did condenser and expansion valves. But it was still pretty good. Compressor never seized up. New drier helps pick up trash, so I’ve been told. No telling what’s wrong with yours. You could try flushing everything again. Evaporators are labor intensive, sometimes. Might want to just replace them. Flush lines, orifices, and new condensor and drier.
     
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  4. McMahons Trucking

    McMahons Trucking Light Load Member

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    Seems like 5 pounds might be high. I had a 377 and it seemed like that took 3.5 to 4 pounds.
     
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  5. Rideandrepair

    Rideandrepair Road Train Member

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    I’m going to guess the bunk has it’s own orifice, simply because my Freightliner has its own expansion valve. I hate to suggest wasting money. But the only things you didn’t do, is flush bunk lines, replace orifice and at least try to flush evaporators. The condensor is definitely suspect. Lines can be flushed easily. Condensor, cannot. I’d say at least a new condensor, flush all the lines again. Flush evaporators, see if they’ll run clear, I doubt it. Orifice only needs a tiny piece of trash,or a piece of ice, the size of a pinheaded to block it up. They’ll Usually freeze up, when bad, or blocked. Turn a/c off let it thaw, and it works again sometimes, till it freezes up again. Sure sign of a bad orifice, or moisture in system. And a new drier again, if going through all the trouble. The only other thing that can affect performance, I’ve learned, is too much oil. It displaces refrigerant. And can actually cause compressor to run hot, and shorten life. I’m not an A/C Tech, so you may want to get more info, before proceeding. Just my experience with my A/C.
     
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  6. Rideandrepair

    Rideandrepair Road Train Member

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    It does sound like a lot. Might be a tag near drier, stating capacity. Too much, will definitely cause problems, usually the compressor will short cycle, staying off longer than on. On the hottest most humid day, Compressor should stay on considerably longer than off. Roughly.
     
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  7. TurnAndBurn

    TurnAndBurn Bobtail Member

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    Appreciate the fast replies. There is a sticker stating 5lbs. Also called Pete with the VIN to confirm. I'm thinking just replacing the condenser, evaporator and dryer. Should a person add any oil when replacing all those parts? You know some oil is in them. But I don't want to put to much in either. Capacity is 300cc. Any good ac flush recommendations.
     
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  8. Rideandrepair

    Rideandrepair Road Train Member

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    The only way to know for sure, is to drain compressor. Measure oil, I think the procedure assumes 1 Oz remains in compressor. Then if hoses are flushed. And new parts.
     
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  9. Rideandrepair

    Rideandrepair Road Train Member

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    4A46DC6D-586D-4771-9E13-E4A0D6996C9F.jpeg Here’s some info I found. I like to use oil with green dye. Makes finding a leak easy. No need for infra light. It shows right up,
     
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  10. Rideandrepair

    Rideandrepair Road Train Member

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    I usually drain compressor, add the proper amount to compressor, minus 1 Oz. Plus add 2 maybe 3oz.at most to accommodate the extra long hoses to bunk.After charging, a little shot from the low side port, and you can feel the oil in the refrigerant. That’s about as close to exact science, I’ve found.
     
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