reversing valve vs compressor

[G Cook]

Can anyone suggest a method of determining whether a compressor is not pumping efficiently or the reversing valve is passing in a split ac system?
The reversing valve can be heard moving.

Thanks in advance.

[DTLarca]

Can anyone suggest a method of determining whether a compressor is not pumping efficiently or the reversing valve is passing in a split ac system?
The reversing valve can be heard moving.

Thanks in advance.

The reversing valve operates on a servo principle. There has to be a certain minimum pressure difference between the two opposing center pipe connections - the one on its own is the discharge and the other in the middle of the 3 connections is the suction. I don't know what a minimum pressure difference on the typical 4-way valve should be? If the compressor cannot develop sufficient pressure difference then of course the valve cannot operate.

I'm wondering if the valve is somehow such that it is diverting discharge to both coils then it would also draw from both coils and so there would be short circuiting at the compressor location and overheating of the refrigerant in circulation there. The pressures would both be lower than normal and possible close enough to each other for the 4-way valve to have now way of moving this way or that.

What do the compressor amps look like?

[chilliwilly]

The reversing valve uses the pressure in the pipework to move the shuttle across the ports and reverse the flow of refrigerant to the coil. If the coil doesn't seat no damage is done to the system as the high and low pressure switches will eventually cut out. As will the klixon or pot overload, and the temperature would not get to the desired setting. The symptoms would be like a condensor or ahu fan not working, or a shortage of gas in the system causing the pot to pump its bollocks of and eventually trip out.

There are other ones that rotate by means of an actuator and reverse the flow. Although I don't think I've ever come across them. You would think by now that the valves would come with limit switches on them, to signal back to the controls, that the change over has taken place. Then restart the compressor and cut down on temperature faults, and display that a fault in the valve has occurred, and to narrow down on misdiagnosis.

[G Cook]

Hi DT

There are 2 identical units side by side so was able to compare, unit which was working correctly was drawing around 9 amps on heating however the other is drawing less, around 6.8 amps, tried adding some refrigerant which increased current draw.

Initially suction pipe from outdoor coil to reversing valve was cold until it reached the valve then from the valve back to the compressor it was hot, i wondered if discharge vapour could have been leaking through into suction?

[DTLarca]

Hi DT

There are 2 identical units side by side so was able to compare, unit which was working correctly was drawing around 9 amps on heating however the other is drawing less, around 6.8 amps, tried adding some refrigerant which increased current draw.

Initially suction pipe from outdoor coil to reversing valve was cold until it reached the valve then from the valve back to the compressor it was hot, i wondered if discharge vapour could have been leaking through into suction?

Coincidentally we had this the other day on a 6kW Mitsi Electric R410A Wall Mounted unit. The symptom and amps sound the same. In the end I said replace the compressor and take a 4-way valve in case. The tech replaced the compressor but it was stalling. I am not sure why the new compressor is stalling but I cam going to go ahead and simply replace the whole outdoor unit - I have no interest in screwing around with this sort of nonsense. The compressor was not delivered on a pallet so I should have immediately rejected - I will reject any compressor from now on that does not come on a pallet and then I will test it before connecting the pipework in future.

But if you had lower amps, like I had hoped for on mine, then we could bet heavily on the compressor - but it seems to me it could just as well be the 4-way valve.

If in doubt order both and price the restocking charge of the most expensive into the price.

I'm going to cut the old 4-way out and slice it open to study and learn ways to test 4-way valves - maybe a way with line tap valves on the suction or discharge capillary connection to add some pressure differential.

Usually if a 4-way valve is stuck you can block the condenser to raise the pressure differential across the bleed holes to blow the debris in them out.

[G Cook]

Cheers DT, glad to see its not just us that have days like today! :D
Seemed to spend most of the afternoon standing in the rain messing about with this thing and made little or no progress!

Thanks for the advice!

[marc5180]

Can anyone suggest a method of determining whether a compressor is not pumping efficiently or the reversing valve is passing in a split ac system?
The reversing valve can be heard moving.

Thanks in advance.

If the reversing valve is passing take the temperature of the pipework across the 4 way rv, this should tell you if it's passing.

[G Cook]

Suction gas leaves the 4way valve at a much higher temperature than when it enters the valve, if that makes any sense.

[DTLarca]

Suction gas leaves the 4way valve at a much higher temperature than when it enters the valve, if that makes any sense.

2 or even 3 degrees warmer is not unusual - by much higher do you mean 10 degrees?

[desA]

These 4-way valves can 'stick'. A slight deflection of the shuttle portion can lock it in place. This can be attributed to a slight tolerance stack-up in the shuttle dimensions.

[G Cook]

I never measured pipe temp, but it would be more than 10 degrees difference. Pipe leaving outdoor coil was cold, not frosting but not far off, however pipe leaving 4way valve was warm right back to comp. There was no frost on outdoor coil, but the little distributor type pipes had a light frost.

Valve was not locked solid as it could be heard moving when coil was removed etc.

[marc5180]

Give the valve body a slight tap with a rubber mallet or something like that, this can sometime release it if it's stuck.

If as you say the Suction gas leaves the 4way rv valve at a much higher temperature than when it enters the valve then it's pretty likely that the valve is stuck in an intermediate position.

[luboboi]

I had mani such cases. 4wai valve replacement