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Ac system pressure gets to high

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  • Ac system pressure gets to high

    After I vacuumed my ac system and let it sit for 30 min to check for leaks, I introduced a 12oz r134 in the low side. The system took the can and the compressor kicked in, the pressure slowly begins to rise. The compressor appears to be working fine, however, the high side, which I had shut off at the manifold and was reading pressure only, kept rising. It went almost to 500psi before the compressor kicked off. The low side started around 40 psi and kept rising as well. Almost to 70psi. This was with one, 12oz can only. When I shut off the engine, the guage are supposed to equalize. The high side quickly dropped to 150psi and the low side shoots up to 300psi. I can only assume the orrifice is clogged. Has any one else experienced something like this? Not sure what is going on. Also, the ac blew cold air only for a bit. Once the pressure got high on the low side, it blew warm air only and I could never get it to blow cold again. 2004 Chevy Silverado 2500hd. Any help is appreciated. Thx.

  • #2
    Welcome Nate: First questions are what happened that you needed to do anything and which engine. I think two versions of a 5.3 V8 were used "HD" changes assorted things throughout these trucks.

    The pressures just are not in line with anything common to me wildly all over the place and seeing 500 ever stand away from this that's going to blow something out near impossible to see that with just 12oz of a charge?? A chart I have shows 25.5oz from empty can be wrong always go by under-hood info if still there.

    Pressures don't equalize with engine off? Are gauges working properly? IDK how this could lock up/seal off high and low side with system off in just a short time after shut down.

    Is this the compressor low under on a small belt manually adjusted just want to know. If those are down for a while in certain situations can collect oil being low and choke, bust that belt or lock it up.

    Has any sealer been used if you know? If so what type usually unknown are not fixes rather just cause problems or fatal to a system.

    IDK, you are only out the 12oz I think I'd get that out, remove "o" tube for a look and condition of oil or metal debris.

    So far it can't cool if this was all new on less than 1/2 charge so no surprise but the pressures are.

    Any other history of recent work on A/C on this?

    All questions, sorry but need to know. Pressure of a real 500 should shut down the system and you said compressor stayed on so info is wrong from gauges or it's been messed with.

    If using the cans with the failed "self sealing" top access with an adaptor I'm not having any luck they are just spraying like nuts losing refrigerant about to side tap those and skip the failed top not one has stayed sealed for me yet but not many tested either.

    Just some FYI, You need to know a full vacuum really did hold in line with your altitude. Yes it should hold but is not proof of no wild leaks just a basic such that you wouldn't continue if it didn't.

    Need lots more info on this see if we can get it going or on to a fix.

    More: HD should also mean coolers for all sorts of fluids in front of condenser, oils, PS fluid, trans fluid all can leak about ruin condenser just look for how much trouble thing could be with some oily mess and dirt up to a total clogged mess so I/we know,
    MetroWest, Boston


    • #3
      A lot is odd here. But generally when you see high pressures that continue to rise with system operation, it is an indication that the system has lots of non-condensable gas in it (air). As the compressor heats the gas, it expands and the pressure rises, the condenser is unable to cool the gas to liquid, (air doesn't liquefy) so the volume stay larger and the process repeats, gas continues to get hotter and pressure higher.
      I would 1st verify the gauge readings, either with another set of gauges or putting those gauges on a known working system and looking at the pressures.
      If truly reaching upper 400 psi, you have a bomb on your hands and a burst hose could leave you blind.
      Next I would draw the system down, pulling from both the low and high sides, until I got as low a reading as possible, then closing the valves and let it sit for an hr or more to look for any rise in pressure.
      Make very sure when adding refrigerant, that you are not adding a slug of air also, purge the lines of air they may have drawn in when you switched over from vacuum pump to refrigerant.
      I have no explanation why the high side would rapidly drop to 150 while the low side would rise to 300! It seams it would be impossible for the low side to exceed the high side, esp by that much.


      • #4
        Originally posted by Tom Greenleaf
        If using the cans with the failed "self sealing" top access with an adaptor I'm not having any luck they are just spraying like nuts losing refrigerant about to side tap those and skip the failed top not one has stayed sealed for me yet but not many tested either.
        Somewhat off topic, but interesting. I decided to buy some R134a cans about 6 month ago, $4.88 at Walmart. Just one can there was the traditional top, the others had that "self-sealing" top. A day later I was at a Walmart or Home depot 3 miles away, bought traditional R13a cans. But if an experienced person cannot get those to seal, sounds like a big SNAFU by industry/government.....


        • #5
          After purchasing a can tapper from Mastercool for the new cans, I haven't had a problem, but haven't use a whole lot of cans on it either. Adaptors are junk, as are a lot of the can tapper sold.
          Too early to tell if it is the cans or the tappers that are causing all the grief.