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high pressure surges in AC system with normal low side pressure

Tom, I do a lot of tech support for both Trane and Copeland and fluttering high side gages are not really a concern. Both a reciprocal compressor and a scroll will discharge gas in pulses. Some compressors have a built in muffler whih smoothes these pulses out but it is for noise reduction. You could have an internal crack of the hot gas system. As other said, many gages now have the needle dampened to eliminate flutter.

I would take the average of the flutter as the saturation point and check your subcool based on that. If charged properly, usually 10 degrees, check the superheat. Usually 8 to 12 degrees with a TXV. Some manuacturers have performance data on expected pressures and amperage with a given load, but that assumes airflow at 400 CFM per ton. Without that data, if you are able to verify the airflow, a wetbulb drop can be used with an enthalpy chart to determine the total capactiy which will help decide if the compressor is efficient or not.

To help further, I'll need to know the saturation pressures, superheat and subcool.


  • Tom_26
    Tom_26 Member Posts: 5

    Have cooling system that was low on R-22 added but high side flucuates very rapidly after running for short period and then will settle down and may do it again after running. Any suggestions ? Sorry Thermal Expansion Valve system
  • Frank_17
    Frank_17 Member Posts: 107
    what kind?

    tsv, cap system or fixed orafice?
  • ta finnegan
    ta finnegan Member Posts: 121

    Did you fix the leak? It had to go somewhere, didn't it?

    Recip. or scroll, heat pump or straight a/c, make, model, size, SEER, age etc.....

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  • Rob_7
    Rob_7 Member Posts: 12

    I would suspect air in the condenser, although that doesn't usually fluxuate much from my experience. Depends on TXV, cap tube, etc, too.
    Also, if you have a restricted cap tube it will normally look like a low charge. If enough refrigerant is added (it can take a lot to make this happen) you can actually fill the condenser up near the top with liquid and get some funny pressures. In either case, it wouldn't, of course, keep up with the cooling load like it's supposed to on a hot day.
    Need more info, but those are just some things to consider.
    Could be the internal pressure relief in the compressor blowing by, too. It's possible that would start when the added charge brought the head pressure up near normal when you added...but only if it was already going bad.
    Just some more things to consider.
  • Ben_3
    Ben_3 Member Posts: 71
    High side

    Tom, TXV systems will "hunt" for their setting until it can establish a load and run at it's set superheat. Air or non-condensibles will usually cause higher than normal head psig. How did you charge the system? With some systems it is necessary to charge by your superheat or subcool. By checking your superheat, subcool, amp draw, and delta tee you will find it gives you a much clearer picture of how the system is running. Much better than the "beer can cold" method.
  • Jack Smith
    Jack Smith Member Posts: 53

    time to recover, repair, evacuate, re-charge
  • Steve Bergerson
    Steve Bergerson Member Posts: 38
    It might be your guages

    How rapidly does your gauge fluctuate? Does it fluctuate so fast that it becomes a blur? If so, you may want to change the gauge on your manifold set to a liquid filled high side gauge.

    Especially on recipricating compressors, standard high side gauges will fluctuate VERY RAPIDLY. We use all glycol filled gauges.
  • ac unit

    air cooled condenser ? what is the outdoor temp and head pressure and indoor temp and suction pressure delta t across evap ie return air temp -supply air temp please read both liquid line temp and suction line temp at the same time as above temps and pressures are read .finally pump down system close suction and run condenser fan without compresser for a few minutes and look at pressure versus outdoor temp should match for r22 you are using r22 right.if pressure is higher than than pressure that would correspand to outdoor temp maybe non condensibles .also read pressure each side of liquid drier or measure temp of line each side do you have suction drier ? check that for pressure drop also.
  • jeff_25
    jeff_25 Member Posts: 110

    also check to make sure the condensor coil is spilt coil type the ones you have that apart and spilt the coil to clean yu could have dirt plugging the 2nd pass jeff
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