2 stage cascade

[wdrzal]

a standard dimmer switch like you use on a light does reduce the voltage. they do make varialbe speed controls for ac motors that change the hertz to control the speed ,but they are not called dimmers.

a light dimmer will harm the motor, should have said reduces current


you are correct I also think the coil is adding too much load.

[pythagoras]

Modern dimmers dont work that way either Walt:

http://home.howstuffworks.com/dimmer-switch.htm

Regards

John.

[_HL4E_HalfLife_]

Its not the dimmer switch , you can't slow a ac motor down buy just reducing the voltage like a dc motor . you will ruin your motor.!!!!!

Don't get me started on what a motor can and cannot do. Motors are my hobby! I've rewound motor stators that have burned out i've replaced sleeve bearings with ball bearings and more I even own the second edition Fourth Impression, Fractional horsepower electric motors By Cyril G. Veinott. And i've seen ceiling fans that use a dimmer switch and if thats not enough take a look at the pic below. Nuff Said!

[wdrzal]

you won't see the voltage drop on a standard multimeter because the sample rate is to slow. however you will see the voltage drop on a scope meter or ocillascope

[_HL4E_HalfLife_]

I still think the real problem is the suction line coiled around the compressor. It should be easy to check if that is the case.

Regards

John.

I asked my boss at work that question and he agrees with me that the tubing wrapped around the compressor won't effect the temps in the loop since the compressor coil is after the loop so most of the gas has already boiled off in the loop section before it even reaches the compressor coil. So I still tend to think that the compressor is too small for stage 1. Prove me wrong.

[pythagoras]

I wasnt denying that there will be momentary voltage drops, you would have to precisely control the switching time to the ac cycle to avoid an off period at the top of the cycle, I'm just pointing out that modern dimmers modus operandi isnt to vary the voltage as part of the operation.

_HL4E_HalfLife_ We dont own people in here, we have discussions sometimes we are right sometimes wrong, its not a competition

Regards

John.

[wdrzal]

every ceiling fan I ever installed that had a dimmer had a rectifier and used a dc motor.

[wdrzal]

dimmers that drop the voltage are also still in sold, usually the cheaper ones

[pythagoras]

Well I dont think thats true, when you add heat the pressure in the coiled section increases-----That is definately fact.

Now if the pressure is increased in this section and its directly connected to the evap the pressure there will increase. If the pressure in the evap increase the evaporating temperature of the refrigerant also increases.

In these systems the only major pressure differences are across the expansion device. There is minimal pressure difference between compresor discharge and expansion device entrance, and a similar minimal pressure difference between expansion device exit and compresor suction.

Regards

John.

[pythagoras]

Well I dont think thats true, when you add heat the pressure in the coiled section increases-----That is definately fact.

Now if the pressure is increased in this section and its directly connected to the evap the pressure there will increase. If the pressure in the evap increase the evaporating temperature of the refrigerant also increases.

In these systems the only major pressure differences are across the expansion device. There is minimal pressure difference between compresor discharge and expansion device entrance, and a similar minimal pressure difference between expansion device exit and compresor suction.

Regards

John.

Actually this is very easy to demonstrate: Stick a hairdryer on that coiled section and watch your evap temp rise

[wdrzal]

as far as the loops even if it alreadly boiled off it can still asorb load in vapor form. thats why you insulate suction lines.

[_HL4E_HalfLife_]

I know ill have to insulate but that still don't account for the roadblock i've run into. My suction pressure was around 10Psi now for R402A that should make the loop somewhere around -35~-45c and yet im nowheres near there and the sight glass is full.

[pythagoras]

If thats 10 psig thats equates to an evap temp of between -10 and -12 Centigrade, pretty close to what you have.

Regards

John.

[pythagoras]

Oooops 10 psig for 402a, thats what you have right? Is -32C.

Now if you have a pressure of 10psig and an evap temp of -15C, one of those readings are wrong. What are you using to measure the temps, if you have already said, I apologise I will read the thread carefully now.

Regards

John.

[wdrzal]

I looked this up to be sure I was correct, this is from copland: heat entering the suction line from ambiant air can cause capacity losses from 10% to 15%.this is why its cost effective to insulate a suction line. thats just a uninsulated suction line in ambiant air, you have it wraped around a hot compressor.that could be over 1/2 your capacity or more gone. you only should have about 10 to 15 degrees of superheat to prevent liquid return,thats it.

[wdrzal]

back to using dimmers, even a modern dimmer that uses a reostat and a triac will harm a ac motor. a ac motor controler uses the same triac, thats where dimmers got the idea from,but because a light dimmer only controls a single filiment the reduction rate doesn't matter. In a ac motor the commutator is divided into many sections for the number of armature windings.Without getting to complex , When the motor is turning, a speed controllor senses these breaks in the commutator and matches the rate at which the motor is turning and supplies even power to each winding. A light dimmer can not do this,and a unbalanced load codition will exist.

I really don't think expensive speed controllors would sell if a dimmer was all that is needed.

[_HL4E_HalfLife_]

Pythagoras- Im using a UEi Digital thermometer. As for my gauges i know there giving an accurate reading. So I would say something else isn't right,couldn't it be because the compressor simply isn't pumping enough fast enough to get the temps any lower?

wdrzal- As i said earlier i've been using dimmer switches to control motor speeds for 10 years now and have never had a dimmer switch die or have a motor on a dimmer switch burn out! thats gotta telling you something.

[wdrzal]

remember the pressure/ temp relationship is only if both liquid and vapor are present.

also a full sight glass apears clear , so does a empty one. they look the same you have judge which it is.

that compresor is designed to run on one speed why would you want to slow it anyhow?

as to dimmers , you can't getto rig stuff in the real world or it will hang you someday. Overloaded stuff causes more fires than anything,don't you think if it could safely slow a ac motor that way the manufacturer would say so!!!!


read up on how a variable speed controlers work, similiar to a triac dimmer but with a very important differance. those triac's were used in motor controllors long before dimmers started to use them.

[_HL4E_HalfLife_]

remember the pressure/ temp relationship is only if both liquid and vapor are present.

also a full sight glass apears clear , so does a empty one. they look the same you have judge which it is.

that compresor is designed to run on one speed why would you want to slow it anyhow?

as to dimmers , you can't getto rig stuff in the real world or it will hang you someday. Overloaded stuff causes more fires than anything,don't you think if it could safely slow a ac motor that way the manufacturer would say so!!!!


read up on how a variable speed controlers work, similiar to a triac dimmer but with a very important differance. those triac's were used in motor controllors long before dimmers started to use them.

1st of all who said anything about slowing the compressor down???
and 2nd the sight glass i have has a FULL word in it that can only be seen when its full.

BTW Please stop treating me like im a rookie at this!

[wdrzal]

you did say condensor motor, thought you said compressor motor. my mistake. never seen a sight glass that says full, what I said about them is true . .

[_HL4E_HalfLife_]

you did say condensor motor, thought you said compressor motor. my mistake. never seen a sight glass that says full, what I said about them is true . .

I could take a pic of it if u want to see.

[wdrzal]

I beleive you, I,m more courius on how it works, what happens to make the word "full" appear. could you explain that.

[kayl]

whats with all the valves?? why so many

[runmc]

Take that suction line off of the compressor..

I love your experiment with the captubes Cool Idea - I hope it works.

[_HL4E_HalfLife_]

whats with all the valves?? why so many

read back a page or 2 its all explained there.