Interesting Problem

Eugene Silberstein 3

Yes, Bob...

That would do it but here's the kicker. There are no liquid line solenoid valves and all of the electrical circuits are operating perfectly.

Hmmmmmmmmmmmmmmmmmmmmmm

Eugene Silberstein 3

2-Stage Air Conditioning System

This situation was brough to my attention by one of my graduating seniors at the college.

Here's the situation.

There is a 10-ton packaged air conditioning system on the roof of a commercial property. The system is made up of two, five ton compressors, each servicing half of the condener coil and half of the evaporator coil (separate loops, of course).

The system operates perfectly when both cooling stages are calling for cooling. Here's the kicker.

When only first stage cooling is being called for, the low side pressure on the first stage pulls into a vacuum and the system does not cool at all.

Mind you, this is a packaged unit (no field piping) and the system cools fine when both Y1 and Y2 are energized.

The system has operated this way since day one and, up until recently, nobody has been able to solve the problem.

Think about it for a while. This is pretty wild.

I ask that the technician who solved the problem to keep it under wraps for a while to let others brood.

Keep smiling!

Blackoakbob

I'll say that ....

since the Y1 compressor starts and runs and also figure the indoor fan runs, then the wiring is correct but the liquid line soleniod coils themselves are physically switched. Hence, the proper operation when Y2 is energized. Those factory guys are always having fun thinking up ways to humble us in the field!
I'm into your Heat Pump book at the moment. I'm brushing up to help my troubleshooting skills and avoid standing in snow up to my ears this winter! Best Regards.

will smith_4

hmmm is right

No liquid line solenoids...control wiring normal, fan normal... what about the first stage TXV? Something's throttling back the flow...

don_163

I think

you got it Will...they strap the bulb for the first stage
expansion valve in the same place they strap the bulb for the second stage expansion valve.

Eugene Silberstein 3

Bulbs are in the correct place

Both of the TXV bulbs are in the right place and, of course, the bulb charges have not been compromised.

Like I said, this has been a problem for YEARS, so all of the "usual" stuff has been checked.

Empire_2

How about this

The liquil lines are crossed!!!!! 1 st stage is actually going into pumpdown throwing its charge into stg #2 as much as it can. The only time the system can get back online is when both stages call and redistribute the total system charge back between themselves.

will smith_4

Saw it on a 10 ton split...

Where the liquid lines were crossed. Assumed that since this is a packaged unit/no field piping, the manufacturer piped it right. So... what ARE the pressures in second stage like when no power is applied but first stage is on?

Empire_2

ES

Please spill... so we know for sure what is the problem...:)

Eugene Silberstein 3

Yes Indeed!

Yes indeed.... The liquid lines were crossed!

Here is a piping diagram showing what was going on. As it operated, there were actually two complete refrigeration cycles for each complete path the refrigerant made through the system.

Took a few years to figure out, considering that we assume that the sytems are piped correctly at the factory.

Empire_2

Interesting

Just when you thought it was safe to go back in the water,.I mean on the roof, someone did the old switch-a roo. No wonder It took so long. You would think that everything is correct from the factory, but then again we are only human. Mistakes are bound to happen. Great call by the student.///
Mike T.