Compressor size changeout (long post)

[Firechicken]

Howdy fellas, i've been lurking for quite some time and decided to sign up and have some fun with phase change and air conditioning with you chaps.


Question about compressor size. I've got a really sweet through wall ac unit that has a monster fan it was only 10,000 btu but it cooled my upper floor pretty nice for it's size.

The compressor recently started getting really tight would not turn on and run against any kind of raised head pressure, i understand it waits for the pressure to come down a tick before cycling again ect and among other issues i'm almost 100% the compressor unit is toast. as once pressure came up and under anykind of load it would start drawing massive amperage and trip the homes breaker.


I had a really sweet 15,000 btu unit with the same connections mounts everything (event coolant type) runs on 120 and dosnt consume many more amps than the 10k unit. Can I get away with using this 15,000 btu unit as a replacement and what would be the illest effects of doing so on a system designed for 10k btu? (other than electronics which i belive i've got figured)

I have made some really nice exact matches of condensor and evap cores that are identicle to the originals to add onto the existing ones, would this be the thing to do to take advantage of the larger compressor unit?

Thanks for any advice you might have appreciate you all having a look at this.

Cheers,

Michael.

[monkey spanners]

Hi Firechicken

Is this a window rattler style unit?
I'd be looking at the start and run capacitors and relay first before condeming the compressor. Capacitors will need replacing long before a compressor unless left too long, in which case they will be the death of it as they fail to produce enough of a kick to start it.

Jon

[wambat]

Sounds like a PSC motor with a bad Run capacitor

[wambat]

Sounds like a PSC motor with a bad run capacitor.

[Firechicken]

Hi Firechicken

Is this a window rattler style unit?
I'd be looking at the start and run capacitors and relay first before condeming the compressor. Capacitors will need replacing long before a compressor unless left too long, in which case they will be the death of it as they fail to produce enough of a kick to start it.

Jon


Howdy Jon, appreciate the reply. Yes it is a window ratteler, actually it is a Through wall unit it has massive coils, massive PCS motor and fans. It dosnt fit in most windows. The electrics are larger than normal aswell and she's al stock bought brand new by my uncle passed down to me at some point. Running on R-22.

OK I will get a replacement relay tomorrow, and the capacitor I will have to get ordered in. Can I get away with a slightly larger cap incase I end up needing to use the 15k btu unit and re-engineer the unit? Now I do understand I would potentially be lowering the torque raising the current draw and lower the power factor some what if used on the 10k unit, I belive I may be able to counteract this with a new circut if absoloutly needed though curious on how much larger I coud get away with period if any at all.

I also failed to mention and I apologise, is that say she's running and purring away under load fan speed dosnt matter, it'll run great for about 15 minits flat out then she slowly starts drawing more and more current on the meter untill lights start to complain and eventually the breaker trips. Could that stilll be caused by say only a slightly weak run side of the capacitor? (it's a dual cap in one run ans start)or would that be hinting more directally at the comp motor in trouble?

Again thanks do much for the help.

Cheers,

Michael.

[Firechicken]

Sounds like a PSC motor with a bad Run capacitor


Howdy Wombat, thanks so much for the reply. AS In my reply to Money Spanners I failed to mention that the unit will run under load great power draws are normal on compressor at startup and run from cold start. After about 15 min of running and working at load she starts to draw slowly more and more current untill the breaker eventually trips.

The cap is a dual cap with start and run in the same housing. Have you seen or heard of bad run sides working just fine for a good 15 min sometimes 20 min and then start to slack off and cause the compressor to over draw?

And also have you seen or heard of the PSC Causing this condition under load (Operating conditions) ? It seems to work fine dosnt seem to get tight ever, but I have not been able to figure out how to measure the motor.


Cheers,

Michael.

[Firechicken]

And finally one more Question I hope one of you gentlemen can help me with. Can anyone give me a basic Procedure on measuring a bad capacitor and PSC motor, so I can figure indeffinatly weather or not compressor is to blame or the cap and fan motor.

Cheers,

Michael.

[taz24]

Hello Michael.

If the comp runs for 15 mins and then fails how long is it before you can run it again?

A few things may be happening and I doubt that it is the fault of a capacitor..

If the comp starts fine and runs fine then stops I would suggest that it is seizing up due to

A lack of oil (Unlikley)
B Heat expansion
C Lack of oil and heat expansion.

If the comp starts to draw more amps then somthing is trying to stop it running to the point of it takeing the breakers out.
This is either caused by somthing getting tight as the thing heats up under use or oil.
Unfortunatly both are unreparable.
You could swap the comp for the larger one (swapping the electrics with it). It will be a little large for the smaller system which could cause complications but if both units are old and not worth spending money on you will not lose anything (except your time) trying the swap..


taz.

Ps Be aware that the system has gas inside and you will have to make that safe before you attemp to remove the comp and then replace.

[Firechicken]

Hey Taz, Appreciate the help very much.

The compressor seems to be able to re-start after anywhere from 3 min minimum to as much as 15 min it seems. It's all over the map really.

I'd also note that the Fan blower motor runs perfect before, during, and after compressor failure on high or low speed dosnt matter

Yes the unit is not worth putting much cash into, but it is a very large size of a through wall unit with stock 10,000 BTU rating. It's much larger than any other through wall units i've seen, even the coils are much larger. I am just enjoying tinkering with it and learning about how she works, and would like to try the 15k btu (known good working order) compressor.

Would youguys be able to offer some extremely rough tips on how much if any size I could add onto the condensor and evap coils in say a percent figure?

Eg. increase Condensor maby 10%, and increase evap size by roughly 5%. Or somthing like this would be great.

I have the materials and supplies to build beautiful coil add ons that look like facory units, so desigining add on to the existing coils is no probblem and i'd like to try it this way for fun.

The unit is a very large size through wall unit, running on 19 oz of r-22, pressures on the tag indicate 120,and 400 psi, for low and high.
it's compressor is 10,000 BTU.
My replacement compressor is 15,000 BTU.

How many percent roughly should I increase the coil size for hot and cold sides to take better advantage of the 15k unit?

Thanks so much. Cheers,

Michael.

PS. I do understand that this is not much better than guessing and flying blind, i'm just looking for a best educated guess for the coil size increase if any needed.

[wambat]

[[QUOTE

The unit is a very large size through wall unit, running on 19 oz of r-22, pressures on the tag indicate 120,and 400 psi, for low and high.
it's compressor is 10,000 BTU.
[/QUOTE]

The pressures indicate the unit has an overcharge and as the unit runs for a short time and the pressures go up the amps increase until it trips the breaker and if the fan cap is defective it could affect the rpm on the fan motor also increasing the head pressure. I hane a digital meter that tells me if a cap is good. You can go here for free: http://www.applianceaid.com/micro4.html

[Firechicken]

Howdy Wombat, thanks for the link. OK I tested the cap based on those instructions and the cap measures as it says it should. The cap is an all in one unit and all terminals test out good.

I was just reading the pressures listed on the factory sticker and I wasnt looking at it but thought it said 120/400 psi for pressure. I Prolly got it wrong and will have a look at the info on the sticker and get back to you.

Interesting on the fan motor. When the fan slows down or is sped up is that directally affecting head pressure, and is that why for cars they always say to put the bower on high for test and fill up?

Thanks again,

Michael.

[wambat]

Fan speed on condenser fan motor is to control head pressure so for R-22 at say 95 *F OSA ambient, the head pressure for an older unit such as yours should be = to about 120/125 saturated condensing temperature(SCT) if the fan has the currect CFM of air accross the condenser; condenser is clean and the refrigerant is the correct amount measured by a 10/15*F sub cooling whan system has a full load on the evaporator. So the head pressure should be about 300# gauge. Of course if the OSA is higher then 95*F then the head pressure will also be higher

[Firechicken]

WOW! thanks for that explination mate, I am taking notes faster than you can type lol very cool how that works.

Checked the factory sticker on the front of the unit again and for pressure it just says Design Pressure : High Side: 400 PSIG Low Side 150PSIG

Rest of the info says Model: CA1016TB-A Serial BM 944094 0390 V-115 HZ 60 Cooling BTU/HR 10000 Amps/A 12.0 Watts 1180 EER 8.5

I know you didnt need all that info just thought i'd ut it up there.

So Is the PSIG reading meaning the reaing you should get on the gage then? I'm sorry i neglected to put that in the other post and ponly said psi, as I see there is between psi, psig, and psi a. Woops sry.

Chers,

Michael

[Firechicken]

Ohh you know what? I was thinking about the blower motor again. Could a defective dissconection switch mechanism inside the unit not be shutting down the start capacitor to take it out of the circut once the fan moterspools up to around 75% of it's speed, thus constantly drawing on the cap not supplying enough to keep the compressor running?

Or dost the Compressor get kicked out and no longer uses the run and start terminals of the cap?.

I was under the impresson that the Compressor unlike the motor is always connected to the run terminal of the cap after it's been started on the start terminal. Maby that could cause inadaquet power and cause the compressor to bog down after it's been running awhile over drawing on the cap and tripping the breakers?

Cheers,

Michael.

[wambat]

High Side: 400 PSIG Low Side 150PSIG

These are test pressures when the Mfg checks for leaks and not the operating pressures. you need to hook up a set of pressure gauges and run the unit for at least 15 minutes to get the actual opeating pressures also I suggest you get a proper education on refrigeraion before you attempt to work of a system. I don't have the time to teach you what it normally takes an apprentice 5 years of schooling in addition to working with various journeymen, to learn, sorry and good luck!

[Larry2]

With an EER of 8.5, I would guess you don't have excess coil capacity to suit a larger compressor. The coil likely has a splash design to make it seem larger than it is. These units splash condensate against the condenser to make it perform better for it's tiny size.

Your other unit that had "lower amps" at 15,000 btu may have required lower amps because it had more efficient coils and better air flow. Moving the heat from the condenser to the outdoor ambient efficiently causes greater capacity or lower power consumption. Similar compressors of the same genre have somewhat similar efficiancy. Differences seem to stem from better coils and less power spent on air flow. Fewer amps mostly will come from lesser pressure differential between the high side and the low side of the compressor. Moving heat sets both of those pressures. It takes coil area and air flow to move heat. A smallish condenser coil will have a higher high side pressure. The compressor will spend power to overcome that. A smallish evaporator coil will have lower suction pressure. The compressor will have to compress that lower pressure to meet the high side operating pressure. Both pressures are set by the coil sizes and their ability to absorb or reject heat. I think the compressor differences are likely to be smaller effects.

I think the important differences in these two units are likely in their coil and air design rather than a better compressor in the 15,000 btu unit.

I'm wondering if you might be low on gas or have an inefficient compressor. Either one will bring inadequate cooling back to the hermetic motor. Remember, the compressor's motor, bearings etc are cooled by cool vapor returning. Loss of charge will cause return vapor to be too warm. So will an inefficient compressor. A dirty condenser coil will make the compressor struggle. We need some measurements to make an educated guess.

You could also have a bad capacitor as suggested. A capacitor that has lost a few MFD will cause the compressor to draw more power and run hotter. The best way to know for sure is by substitution of a correct value part. A meter won't check it under load, though it will check the value. Split phase motors have a sweet spot for the capacitor value. Too high or too low will make them draw more power while not doing any more work. That difference is heat. Mostly, old capacitors get lower in value from leaking electrolyte and drying out. They can short too, so you need to check leakage as well as value.

Check the coils for dust, dirt and debris. You could pull the cover off and flush the coils through with soapy water. If they are dirty, they will wreck performance. Be sure to protect the electricals while doing this and let the unit dry completely for testing. While you're at it, clean dirt and debris from the fan cage.

Can you make some measurements on the unit?

You didn't mention if the unit has remained sealed as shipped from the factory or has tappers added and has been tinkered with. Assuming it has not been worked on, there should not be air, water or junk inside.

I don't think you'll be happy swapping the compressor with a different capacity compressor on a capillary tube system, which most of these shakers are. You may have to figure out new capillary tube sizing and that's not as simple a task as the little coiled tube part implies. I doubt I could get it right trial and error.

[Firechicken]

High Side: 400 PSIG Low Side 150PSIG

These are test pressures when the Mfg checks for leaks and not the operating pressures. you need to hook up a set of pressure gauges and run the unit for at least 15 minutes to get the actual opeating pressures also I suggest you get a proper education on refrigeraion before you attempt to work of a system. I don't have the time to teach you what it normally takes an apprentice 5 years of schooling in addition to working with various journeymen, to learn, sorry and good luck!


Howdy wombat, no worries. I am not completely oblivious to the rigging, I am a a red seal, Licenced Journyman Heavy mechanic and have already spent 5 years on the floor. The reason I ask and word this stuff the way I do is I dont know everything, as I am not an HVAC tech. While I am not an AC specialized tech for the ac systems field of my work I still have to work with it from time to time, and having that attitude in the perscence of guys that know what the heck thier doing around this awsome forum I go right back to the basics with questions. I have theorys schematics, test equipment, hearing some of this from another that knows what they are doing is nothig but gold. and I'd ask 10 different guys the same question and get slightly different tkes on it, thats where the gold to larning lies and why I do it. HVAC & R is very different in alot of aspects and very similar aswell. Simply asking the way I have been has neted me with alot of very direct answers that I treat with opinions only as your right noone can dictate to someone over a forum how to learn a trade overnight. I wouldnt expect you to grasp how to time heavy injection pumps either, but know you could do it properly with the right inquiry and study at home. and combined with my study and hitting books hard on hvac I am gaining enough to fek about with a worthless unit.

I have sweated an access port onto the lines and recovered the reff. with our unit at the shop already. I am not some ignorant knob letting the crap go into our air or anything like that.

It's just a fun project I wish to timker with at home on the weekends, I will document the process with good quality photos aswell for you guys to see the process. I have some really nice new cores I built and have a really cool housing unit and controll system thats almost together I think you'll enjoy. Thanks for the help appreciate it.

Michael.

[wambat]

Hi Michal, My dad was an immigrant from St. Marcel, Canada and I have a lot of relatives there but I don't know them and I can't speek French which was my Parent's native language. I admire your perserverence to learn, keep it up! :)

[Firechicken]

Howdy Larry2. Thanks for the info. Pure Gold mate. I'd deffinatly like to ask a couple questions concerning cap tube sizes and length selection aswell, but I think i'll do a new thread for that one once i'm ready to finish up the new chassis and mounting points. Hopfully by next weekend i'll have the new chassis mounting and assembly done, and the rest of my new parts to handle the new electrics arrive.

I am quite enjoying myself alot with deciding on the ways to control the fan speeds, run temp control ect with my AC and heating digital thermostat I've got, theres so many ways a guy can setup the control electrics the choices are endless. I'm like a kid in a candy store on this project for some reason.

I'll keep you fellas up to date on progress and get some pictures up as soon as I can get them done.

Cheers, Michael.