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  • Compressor cycling frequency

    Hello all, first post. I have 2016 dodge grand caravan with the dual ac (front & rear) setup. My question is how often should the
    ac compressor cycle on and off during normal operation? My ac is blowing about 42 F out the vents but compressor
    cycles every 15 - 20 seconds. I have no idea if this is excessive or normal. I had a local shop pull the freon, vacuum the system and
    put the right amount of freon back in. But the compressor still cycles as indicated. Need to know about that. If there is a problem, what
    might it be? What might be a solution? Thanks for the help. Tater John

  • #2
    Does it stay blowing 42F or close out a center vent? If a CCOT (think so for now) set up that's as cool as it would or risk freezing so is normal.

    It's been to a shop did what is suggested if they thought it was within norms keep live watching outputs also know real air temp outside will run longer the hotter normally and less if cooler too.

    A possible 8 years old watch it when it's not putting out expectedly go back to find a likely leak hope there's now dye in it helps.

    It's controlled by lots of sensors, fan speeds vs many other inputs. To me the most common issue is leaks first if this lasts the season it so slow isn't easy to find,
    Last edited by Tom Greenleaf; 06-22-2023, 09:11 AM.
    Tom
    MetroWest, Boston

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    • #3
      Rockauto shows it to be a Tx valve system, with a pressure transducer to control it. (Looking up on R/A is a quick way to find what type of system)
      You could try throwing a transducer on it, under $40, or you can take it to someone with the correct tools to diagnose. A transducer as about as much as I'd risk if you go the "throwing parts at it method".
      A Tx valve system will cycle the compressor, just not that fast. The only one that don't are the systems with some sort of evaporator pressure regulator. They were common in the 60's but went way when fuel economy became paramount.

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      • #4
        Just note a hyperlink I didn't add was in post #2! I re-wrote it????
        While here to taterjohn, what prompted you to complain and seek help? I think I hear fine usually don't hear cycling while inside driving anything so asking,
        Tom
        MetroWest, Boston

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        • #5
          Sorry so late to respond, some unpleasant dental work has delayed me.
          I appreciate very much the replies regarding my question, but must confess I'm somewhat ignorant to understand all the questions asked of me. Regarding hearing the compressor cycle, I am referring to when it is at idle. I cannot hear it cycle when driving down the road either, my hearing is very bad anyway. When I posted previously I forgot to include a thing or two. At first my A/C was blowing 60 degrees. A buddy came over with manifold gauges and we put in freon based on the temperature chart and the low / high pressure settings, and got it to blowing 42 degrees out the vents. However, the compressor was cycling about every 15-20 seconds, and the high side was getting up to 300, the low side to 30, didn't seem right. So that's when I took it to a shop to pull all the freon and run a vacuum and put in the right amount. They did so but compressor still cycling the same. ALSO it is only blowing 60 degrees instead of the 42 degrees as when I took it to the shop. I don't know if they put in the wrong amount of freon or what. The sticker on the front of the van shows two amounts of freon, one for the single A/C and a larger amount for the dual A/C system, which I have. I have driven it about 80 miles since the visit to the shop and it is consistently blowing 60 degrees. I'm not sure what to do now except since the shop supposedly put the right amt. of freon in the system, I think I will have my friend hook his gauges back up to just see what the readings are for future reference, and go from there. Any suggestions? Sorry so long a post.

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          • #6
            If you are a gambling man, I would buy a transducer and replace the one that is in there now. It is just a guess, but not an expensive "guess".
            No way to get the amount correct pressure charts, especially if there is something wrong with the system. They can help if the system is KNOWN to be charged correctly, they can point to other problems, but can't be used in reverse to measure when the system has the correct charge.
            The correct way to diagnose would be to operate with gauges on and look at what temps are doing at the condenser and evaporator and look at the pressures at the same time.
            $30 or so for a transducer is a cheap alternative. May be all it is, or may not, but it is what sends the signal to the HVAC controller, which in turn controls the compressor. It IS NOT a switch, don't go jumping terminals!

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            • #7
              Is rear A/C in play when observing things? Pleading IDK right now many use or used to CCOT with rear on expansion valve would hog the bounty.

              Pressures aren't going to help without knowing temps coming in thru grille at that time AND should shut off rear A/C.

              60F outputs are too high if you asked for A/C adding refrigerant especially a dual system has one compressor can be too much now??

              It's hard without all temp factors and time A/C has been on. Super hot interior it has a battle to overcome lots of airspace in these.

              I still maintain that leaks are the first cause of issues next is improper messing with the charge amount if not vacuumed totally and put back exactly listed amount count what came out helps a lot is costly equipment to know that.

              If lacking all of it pressures - use just front. Take temp coming in 1 foot in front of grille takes some work. I've used a household wired thermo on a stick if nothing better for the guess.

              Presumably sitting still air under fan power could blow out front so it's not so easy long time high pressure switches can cause shut off hotter than you thought.

              No jumping things let it do it's thing take fast accurate observations even try to close hood if you can airflow with it open isn't reality. Just noting not to just go adding now if how much was added hurt performance should consider starting all over fill from empty/evacuated then things should make more sense with performance.

              Leak finding if active is still hard sometimes I won't expound now on how,
              Tom
              MetroWest, Boston

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              • #8
                Tom,
                For what it is worth, Rock Auto shows a block type Tx for both front and rear. I have no personal knowledge to say it is or isn't correct.

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                • #9
                  OK, Not strong on what Mopar will do. Found a Mitsubishi engine in one lots older that this used the block Tx also ages ago. Issues seemed always a challenge to control heat transfer for engines and of course A/C just made it harder yet lots of stuff jammed in a small area. Popular things from the get go,
                  Tom
                  MetroWest, Boston

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