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  1. #1

    Suction running in vacuum, high side pressure not high, 404a freezer

    I have a freezer truck with a Copeland condensing unit (TJAL-030Z-CFV-300) and cold plates inside. It has one TXV for each cold plate. The issue is the suction line quickly runs into a deep vacuum after the compressor starts so the pressure switch does its job and shuts it off. After not finding any leaks, I bypassed the pressure switch for a short test run and it ran fine except for pulling almost 20 inches of vacuum. The high side pressure isn't climbing up like I expected (more familiar with car A/C). The condenser is clean and the fan is working. The pressure in the system isn't equalizing after the compressor is shut off. It does have a CPR valve but when I hook up my gauge before the CPR, it is also in vacuum. So it certainly appears there's a blockage issue. I tried to recover the 404a from the 'king' valve at the compressor, but it just wasn't flowing. At the receiver, it came out nice and fast to my recovery tank and pumped out nicely too (I have an old Promax machine). So it would appear there's a blockage somewhere between the compressor and receiver. That would narrow it down to something internal in the receiver (dip tube maybe?), condenser, or small spun brass brazed-in filter between compressor and condenser. Any easy way to find out where the problem is? Is this a common issue?
    I recovered all the refrigerant and it wasn't low or overcharged... but had to recover it from the port on the receiver as it was just trickling out at the compressor, would have probably taken days to get it from there.

  2. #2
    Join Date
    Oct 2001
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    6,966
    the KING valve is at the condenser was it the suction or discharge service you couldn't pull from? might be the power element on the TXV is the cap tube worn and blew its charge,basically the unit is pumping down into the receiver! LL dryer or TXV power element is my guess
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  3. #3
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    Aug 2012
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    willowick ,oh
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    You have to see what actually operates the system. Does the tstat just turn off the system or does it pump down off of a liquid line solenoid on low pressure. If you are going in a vaccum then there is a 95 to 100 percent restriction. Make sure all isolation valves like on the receiver and so forth are open.

  4. #4
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  5. #5
    Join Date
    Oct 2008
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    Ohio, USA
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    I doubt you have a major restriction on the liquid line before the receiver. You would have some serious head pressure if you did, because you would stacking the condenser with all your charge.

    Also, if you ever DO have a restriction in the liquid line, e.g. filter drier, its very easy to tell because there will be a noticeable temp drop. Sometimes enough to frost.

    You mention it has 2 TXVs - Do they seem to be operating at the same temp?

    Are you familiar with rotolock valves and how they isolate?

    Do you have solid liquid through the sight glass? Is so ---> do you have solid liquid to the TXVs?

  6. #6
    Join Date
    Jul 2012
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    Western KY
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    First if your pulling into vaccume something is wrong with your low pressure stitch, what is its cut out setting? Cold plates take alot of refrigerant and you may simply be low on charge. Really need more info. If it is simply a charge issue you can tell by sticking your hear in the truck and have someone start the system if you hear gas hissing through TXVs your low. No hissing your restricted or a valve is closed somewhere. Good luck.

  7. #7
    Join Date
    Oct 2011
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    or small spun brass brazed-in filter between compressor and condenser
    ??? Could this be a muffler? Leaks are common on reefer trucks. If there is a restriction, it's more than likely in the drier or txv's. Loss of charge on the power head could also be an issue.
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  8. #8
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    Sep 2008
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    Quote Originally Posted by Jared Fetter View Post
    I doubt you have a major restriction on the liquid line before the receiver. You would have some serious head pressure if you did, because you would stacking the condenser with all your charge.

    Also, if you ever DO have a restriction in the liquid line, e.g. filter drier, its very easy to tell because there will be a noticeable temp drop. Sometimes enough to frost.

    You mention it has 2 TXVs - Do they seem to be operating at the same temp?

    Are you familiar with rotolock valves and how they isolate?

    Do you have solid liquid through the sight glass? Is so ---> do you have solid liquid to the TXVs?
    This is not always true.


    If it has reached the 'noticeable temperature difference' stage, it has been plugged for quite a while.

  9. #9
    Join Date
    Oct 2008
    Location
    Ohio, USA
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    Quote Originally Posted by jpsmith1cm View Post


    If it has reached the 'noticeable temperature difference' stage, it has been plugged for quite a while.
    I don't know if I'd say time is any way indicative.
    Perhaps a more accurate way to describe it, would be to say it is quite restricted to cause a very noticeable temperature difference.

    It could be a filter slowly plugging from sludged oil and contamination, or it could be a filter plugged within an hour from a large system breakdown.

  10. #10
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    If his restriction is bad enough, he may very well not read any temperature drop, because no refrigerant is flowing.

    Since he has multiple cold plates, I'm steering away from multiple bad power heads. And am going with he has a main liquid line solenoid valve not opening for whatever reason. T-stat, Time clock, bad coil...whatever it may be.

    OP: your head pressure isn't climbing like you'd expect it to, because your refrigerant isn't doing any work.

  11. #11
    Join Date
    Aug 2012
    Location
    Upstate, SC
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    With the box at outdoor temp, fire it up. Watch all the lines closely, if you see any line between the compressor and the TXV's frosting or even sweating, there's your restriction. that is if you know that the charge is right. if you don't see anything pretty quick, check inside and see if it's getting cool at all. if not then your restriction is prob in your suction line.

  12. #12
    Join Date
    Aug 2012
    Location
    willowick ,oh
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    261
    I agree with phaseloss. we need more info on this setup.If the sysem operates off of a LLS then the low pressure cutout is either waaaay too low or it is bypassed or it failed,therefore causing the unit to constantly pump down. You may have multiple issues but we dont have enough info.If it doesnt have a LLS then it may be low on charge, possibly but that is when you take your sh and sc

  13. #13
    Join Date
    Apr 2004
    Location
    NJ
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    155
    Since he has multiple cold plates, I'm steering away from multiple bad power heads. And am going with he has a main liquid line solenoid valve not opening for whatever reason. T-stat, Time clock, bad coil...whatever it may be.
    Solenoid closed most likely, but were the txv strainers checked? If one clogs, they both will. Since the system is recovered, open the solenoid and remove the "guts" (diaphragm, plunger etc). Put the plate back on, check the txv strainers and see what happens. Of course, check the solenoid electrically 1st!

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