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jakb21599
11-02-2011, 04:06 PM
Hello friends, have a question about a 1 hp semi-hermatic compressor for a freezer display case. 401A *****. The question is this. You can feel and hear the suction line pulsating from the compressor all the way to the case inside the store. While the high and low side guages are attached. The low side is steady but the high side is bouncing around so much you cant tell what the high side pressure is on the guages. Is this because of moisture in the line ? It has been working fine for the past 2 years and no work has been done on it. In the past i have been told when the high side needle bounces it is because moisture is in the system. Is this true? Also what else could cause this needle bouncing so i can futher investigate. Thanks for your help

Tayters
11-02-2011, 07:22 PM
Maybe a dodgy discharge reed valve. As the piston goes up some of the gas squirts out the side of the faulty valve causing the pressure fluctuations. The net result would be less refrigerant compressed therefore lower head pressure. Perhaps it isn't enough of a leak to cause a noticable effect on the system performance.

Moisture causing it? Well, not sure on that one but I can't see it myself. More likely to cause ice blockage/acid formation rather than bad vibes I'd have thought. Is there a moisture indicator in the system that could assist you?

Andy.

Tesla
12-02-2011, 06:45 AM
Hi jakb
Like Tayters said first check the discharge valve - close off (back seat) the service port to restrict the pressure a little on your gauge to help dampen the fluctuation and check for decreased discharge pressure, feel for a warmer/hot crankcase, use a big long screw driver with handle on lower part of ear to help locate source. Also check if fitted discharge muffler or restriction in discharge line if the pressure is high. I have only had four cases where this type of noise resulted, liquid slugging (shook the whole store), discharge muffler removed (vibrated whole chiller and mech board), harmonic resonance at certain load (two big recips SOG) and a R404a rack which was someone else's problem. There could also be a dented pipe somewhere. Is the noise constant throughout the whole cycle or does it come and go?

jakb21599
13-02-2011, 01:08 AM
there is not a site glass in the system to see if any moisture is present. I back seated the discharge and pressure was about 150 psi. checked the piping and no kinks or restrictions. the noise is constant and does not come and go. so matbe it is what Tayters saying about valve ? another weird thing is that any where on the suction line in the line set you can hear and feel pulsating. Why is it only on the suction line and not liquid line ?

Tesla
13-02-2011, 03:54 AM
Hi jakb
It has been over a decade since I worked on a meat freezer case and cannot remember what the pressures should be but you should know if the head pressure is normal or not. The only other things I can suggest to check would be the basics like SH and SC and any control valves in the system like TEV, solanoid and Back Pressure Regulating Valve. Are the temps ok and if the reed valve is shoot what caused it - is there any flood back (hence SH check). It may even pay to fit a schrouder valve at evap outlet to check pressure and SH. I'm sure someone here could almost point you directly to the problem.

nike123
13-02-2011, 05:06 AM
You can feel and hear the suction line pulsating from the compressor all the way to the case inside the store. While the high and low side guages are attached. The low side is steady but the high side is bouncing around so much you cant tell what the high side pressure is on the guages.

This sound contradictory!!
What is the case? High side pressure is bouncing or low side pressure is bouncing?
High side could bounce if construction of compressor is such that no volume is present after discharge valve. I seen that many times and, especially when you have gauge which is not filed with oil to compensate/smooth that.
Compressor need to have some large volume to smooth his discharging action. If construction is such that no large volume is present after discharge valve, than it is normal that you see needle bouncing. That is like car silencer.