2001 Pete 379 A/C issue

Discussion in 'Peterbilt Forum' started by GrapeApe, Sep 19, 2014.

  1. GrapeApe

    GrapeApe Road Train Member

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    We have a 2000 Pete 379 with a C15 that blew the A/C compressor and filled the system with metal trash. Condenser was looking rough, so we just replaced it, the front evap core also looked rough, so I said the heck with it and we replaced both. The front evap core came with a new orifice tube, the rear came with a new expansion valve. New compressor and accumulator obviously.

    So all we were left to flush was the hoses, which we flushed with the A/C flush solvent and air (Robinair flush machine). Everything else in the plumbing is new. Compressor came precharged with 300cc's of oil and the manual says 300cc's is the whole system charge. Our Robinair machine defaults to a 15 min vacuum, but I set it for 30 min to make sure and charged to 5.00 lbs like the manual calls for.

    OK, now the issue. Low side pressure, 35-40, high side will not go over 150 psi, it just stays right at 150. It was 65 degrees out today. Front A/C is cold, but not as cold as it should be (38 degrees), rear A/C is not working (63 degrees). All of our other Petes will slowly build pressure to about 300 psi, then the fan kicks on and pulls the pressure back down. The other truck we had in today was blowing 27 degrees.

    My first thought was maybe we didn't get the lines fully clean and something got in the expansion valve in the bunk, it's acting like it was stuck open? So I recovered and checked both the expansion valve and the orifice tube screen, clean as a whistle, no signs of any debris. That was then end of the day, so I put it the lines back on, pulled a vacuum on the system and went home.

    So now I'm wondering what to do tomorrow. We stock expansion valves, even though it's new, should I swap it out? Am I thinking in the right direction? The rear evap core was cool to the touch, not cold. The high pressure line to the bunk was warm, the low pressure line was cool, not cold. The blend door flap is working correctly. On the front, the high pressure line was warm, the low pressure line was much colder than the bunk.
     
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  3. baha

    baha Road Train Member

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    Pull the screen and see what is caught,? again
     
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  4. walterjacobo15

    walterjacobo15 Light Load Member

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    Aug 23, 2014
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    Pressures are normal for 65 deg. temp...


    [​IMG]

    I would re do orifice tube (BTW check for proper orientation) I might also blow some compressed air, high side to low side just to make sure nothings is stuck in there. Dryer OK?
     
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  5. QUALITYTRUCK

    QUALITYTRUCK Road Train Member

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    you have blockage for sure.those # are not normal.after removal of parts, I think some shop air blasts are in order.good luck.
     
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  6. GrapeApe

    GrapeApe Road Train Member

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    Thanks for all the replies. It seems that the expansion valve was stuck closed. I double checked the orifice in the front, the screen was squeaky clean. I disconnected all the hoses and blew through, the expansion valve in the back would flow very little compared to a new one. I didn't see any debris in it, but it was not full open at room temp. Replaced the valve and just in case it was debris, I replace the accumulator....again. On break now while it's under vacuum...again.

    Honestly, I have very little experience in the dual system and still getting a grasp of it. I've done plenty of day cab work and cars. They are either expansion valve or fixed orifice, not both. Not that it matters for a blockage diagnosis, but still not 100% confortable working on them.

    With fixed orifice up front and expansion valve in the rear. If a driver say has the front fan on low and turns the rear up to max, how does the front not freeze up? The compressor would be running enough to feed the rear on high, but you can't slow refridgerant through the front.
     
  7. GrapeApe

    GrapeApe Road Train Member

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    Running cold now front and rear, 27 degrees up front and 30 in the rear. I'd have to guess that a small left over chunk plugged up the expansion valve. Slowly builds up to 300 psi, the engine fan kicks in and pulls it back down to about 175, it cyles like that every 6-7 min.

    Thanks for the help.
     
  8. QUALITYTRUCK

    QUALITYTRUCK Road Train Member

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    Good job.This time of year we are all a little tired of the a/c work performed all summer.It is the only repair that has electrical,hydraulic and mechanical aspects that have to be working.
     
  9. tw1005tx

    tw1005tx Light Load Member

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    I found this a good post I drive a similar tk and wondered about what was happened when the rear unit wasn't being used, didn't know that the rear was a expansion valve where is the orifice tube located for the front. I would think the front evap would have temp SW to cycle the clutch if it got too cold.
     
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