How's Dual Compressors work?

[seanhoang]

Hello, need some help explaining this situation. A customer of mine has a game room that works on ONLY one unit with dual compressor. He initially has two workable packaging units, but for whatever reason only one is now hooked up to the building. Because of the heat load inside the building, the compressor #1 will tripped and he has to go and reset the high pressure switch. It will run for about five minutes and tripped and the compressor #2 kicks in. The second will keep running and never tripped. Compressor #1 seems to govern the ductwork around the thermostat area and when tripped will blow out hot air. Compressor #2 seems to govern the middle part of the room and blows out cool air. In addition, he has invested two portable units that are hooked up around the opposite wall of the thermostat because there are no air duct around that area. Okay, so here’s a few of his questions:

1. How do these two compressors work hand in hand with each other? Are there two separate coils for each compressor – one feeding to one area of the room and the other to the other area of the room?
2. Why is compressor #1 keeps tripping and compressor #2 never trips? Can we conclude that compressor #1 is bad?
3. If we replace compressor #1, will we resolve the problem? Can we take the compressor from the other unit (one that is not hook up) and replace it onto compressor #1?
4. Why is the section around the thermostat area hot when compressor #1 tripped and the middle section stays cool? When not tripping all areas is cool.

I really need some guidance because I can’t seem to explain it clearly to him. Please help.

[manny238]

1. sounds like you need to go to your friends shop and inspect all the equipment for yourself.
2. you need to guage up to the unit and see what your pressures are to see why the #1 compressor is tripping.
3. your asking for trouble if you start gutting unit to fix another
4. who knows. check supply duct dampers to see if any are closed

in conclusion if your not a certified hvac tech. you need to call a professional

[Saturated Suter]

All repairing, testing and subsequent addition or removal of refrigerant should be done by qualified and EPA-licensed refrigeration technicians.

**Resetting the safety switches repeatedly sound like a great way to cook the oil, contaminate the refrigerant and/or otherwise burnout the compressor.

If you want it to last, pay for a service call.

Hope this helped.

[seanhoang]

I am a certified HVAC technician by the way, but haven't been in the business for a long time. Well let me simplified the question then since the previous work was probably a hacked job. Can anyone explained dual compressor, how it works and how it hook up to the evaporator coil?

I've read somewhere that it's a 2 stage compressor, compressor #1 kicks in and work and compressor #2 kicks in if there's more heat load. In that case, can we assumed that compressor #2 will NEVER kick in if compressor #1 will ALWAYS satisfied the heat load. In other word, compressor #2 will never be in used. And also in that case, we can assumed that in this scenario (I'm talking about this customer) it's time to replaced compressor #1 and also fix the heat load issues in the building.

Greatly appreciate any details!!!

[hvac69]

Dual compressor system may be have separate evap coils and refigeration systems or they may share the refrigeration circuit. Either way they are staged according to load compressor 1 may not always be first on, if lead/lag is being used. You may have each compressors refrigeration circuit feeding two different air handlers. Doubt you have bad compressor if you can trip the high pressure safety.

Certified and qualified or completely different animals.

[kls-ccc]

How it works will depend on what type of system it is. With what you have discribed I would guess there are individual circuits for each compressor, but it may not be the case.

Tip: Know what you are working on before you try to fix it. If you don't know, wallk away. I have been in this business 33 yrs, I always want to try to learn something but I also know when to walk away.

[seanhoang]

Thanks for the info KLS and HVAC69.

So what you guys are saying is that this unit (with 2 compressors) can either be hooked up to one evap coil or two individual evap coils. I'm getting the feeling that this unit is hooked up to two individual coils because compressor #1 keep tripping and the area around the thermostat is hot while the middle area of the room is still cool and that compressor #2 never trips.

But guys, you haven't explain how dual compressors work?

[david chamberla]

it works off a 2 stage stat when the temp in the rm can not hold than it will start 2nd stage when trouble shooting at first think of them as seperate units ,r,s.e.s says better knowledge through education i hope this helps

[SoFlaDave]

I'm confused, is there 2 compressors or 1 dual speed compressor?

[ruuufuhbock]

Sounds like from the op its 2 compressors, 2 circuits. And one circuit is going out on high head. But imo sounds like compressor is fine. More likely that condenser is dirty or something along those lines. Seanhoang do you have any more info on the unit or operating pressures, sh, sc, anything like that...the more the better

[seanhoang]

This one unit houses 2 compressors and the one closes to the nameplate is tripping every 5 minutes and high pressure switch has to be reset. Initially it was overcharged with 85psi low side and 300psi high side and increasing. We recovered some of the refrigerant down to 75psi and I don't remembered the high side, but the unit wasn't tripping, but is wasn't a hot day. Then a week later, when the weather got hotter, compressor #1 starts tripping again.

I am just curious if this unit is hooked up to two individual evaporator coils because the section of the room where the thermostat is is hot when tripped. Or is it just hooked up to one evap coil.

[seanhoang]

Oh by the way, we clean the condenser but didn't get the superheat or subcooling readings.

[A-TEAM]

if the suction was 75psig on a cool day it might still be over charged, but knowing super heat and sub cooling would be nice and if you just look in the attic you should be able to figure out if there are two evaporators cooling that room

[y7turbo]

This one unit houses 2 compressors and the one closes to the nameplate is tripping every 5 minutes and high pressure switch has to be reset. Initially it was overcharged with 85psi low side and 300psi high side and increasing. We recovered some of the refrigerant down to 75psi and I don't remembered the high side, but the unit wasn't tripping, but is wasn't a hot day. Then a week later, when the weather got hotter, compressor #1 starts tripping again.

I am just curious if this unit is hooked up to two individual evaporator coils because the section of the room where the thermostat is is hot when tripped. Or is it just hooked up to one evap coil.

You're the one who looks at the equipment, we're just reading what you type on the computer screen. How do we know how the unit is piped?

For help you're going to need to post IN DETAIL everything about the system. We dont know if its got a 2 circuit evap. It can go either way, 2 compressors and 1 circuit coil or 2 compressors but different refrigerant circuits.

Can you provide model numbers or maybe a brand?

Does it have a multi layer condenser coil that you need to split apart and clean in between the layers?

[manny238]

This one unit houses 2 compressors and the one closes to the nameplate is tripping every 5 minutes and high pressure switch has to be reset. Initially it was overcharged with 85psi low side and 300psi high side and increasing. We recovered some of the refrigerant down to 75psi and I don't remembered the high side, but the unit wasn't tripping, but is wasn't a hot day. Then a week later, when the weather got hotter, compressor #1 starts tripping again.

I am just curious if this unit is hooked up to two individual evaporator coils because the section of the room where the thermostat is is hot when tripped. Or is it just hooked up to one evap coil.


Was the unit running 85 suction with 1 compressor running or 2? If this is a tandem compressor set-up that suction pressure is normal for 1 compressor running.

Why dont you just go follow the pipe work for the unit. No one here is gonna know if you have 2 evap coils or 1.

[A-TEAM]

what does RTFM mean

[cjpwalker]

what does RTFM mean

Read the Effing Manual. A last resort, yes, but sound advice.

[jackintheboxtec]

You ned to give us a model and serial number or this thread will go now where. Everyone will just be guessing. :gah:

Oh!! by the way call a "PRO" before you hurt yourself and someone else!!:whistle:

[MUNC]

Trace the line sets, look at duct work it's not rocket science. With out subcooling reading (txv) how do you know if your over charged? i agree with look for a split cond coil. If compressors are two diff tonnage and #1 has greater capacity( normal) and trips but #2 doesn't, could be either cond dirt or over charged. but if both comps are the same size and 2 runs look at over charge. either way not enough info, we all could sit and guess for ever

[seanhoang]

Thanks guys for the information. Sorry I'm new. I'll post better description next time.

[allan38]

Many two compressor condensers have circuit 1 piped in at the top or bottom of the coil and circuit 2 on other side. I can envision several ways the top or bottom of the coil could be clogged and causing one circuit to trip out on high pressure. Even when the coil looks good on the outside, some two layer coils will trap debris between them.

Some designs make it hard to figure subcooling, particularly if they have the high side pressure tap on the compressor discharge portion of the circuit and not on the liquid line portion of the circuit. Some manufacturers include performance data with their equipment. This data will tell you the expected pressures at specific performance conditions.

I've learned a lot when I RTFM (Read the Funny Manual).