2.5 ton compressor wont run.. SOMETIMES???

this is a residential AC unit, R22 refigerant , coopland compressor, it runs fine the charge is good. but it will not start some times. it seems to be going out on thermal overload all the time but it doesnt seem to be overheating.

my thought is the internal thermal overload protection is bad.

however my question is the TXV seems to be staying closed because the high psi line is running at around 170 psi. BUT WHEN THE COMPRESSOR SHUTS OFF the pressure doesnt equal out. the high psi side (red side of guage) stays at 170psi while its not running.

is this normal with a TXV? is that why the compressor wont start again for a while becasue the txv is stuck closed? its not overcharged. just shuts off and wont start again for a while all the time.

any help with this high pressure while unuit is off due to txv stuck closed? would be appreciated thank you

Need some info, is the compressor hot ? What amps is the compressor pulling on start and run? What is the gauge pressures when running ? Is unit cutting out on lp switch ? Is unit cooling effectively ? At 170 psi Seems low refrigerant level what ambient temperature is it ?

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Originally Posted by kurt854

this is a residential AC unit, R22 refigerant , coopland compressor, it runs fine the charge is good. but it will not start some times. it seems to be going out on thermal overload all the time but it doesnt seem to be overheating.

my thought is the internal thermal overload protection is bad.

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You must find out what exactly shuts compressor down. Could be low pressure switch, high pressure switch or something else if contactor de-energize compressor. If contactor stays energized and compressor wont run, than it is internal overload acting.

What is your discharge superheat? What is your suction superheat? What is your suction pressure? What is running and FLA current? What is compressor model no.?

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however my question is the TXV seems to be staying closed because the high psi line is running at around 170 psi. BUT WHEN THE COMPRESSOR SHUTS OFF the pressure doesnt equal out. the high psi side (red side of guage) stays at 170psi while its not running.

is this normal with a TXV? is that why the compressor wont start again for a while becasue the txv is stuck closed? its not overcharged. just shuts off and wont start again for a while all the time.

any help with this high pressure while unuit is off due to txv stuck closed? would be appreciated thank you

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It doesn't equalize immediately. It needs time, but eventually it is going to be equalized.

i dont believe there is and low or high pressure switch. its just a simple residential 2.5 ton unit.

all it has is a thermal overload (witch is internal) , or i would just bypass it and see if would stay running. i dont have the amps or sperheat numbers now., but i think there all ok.

i am sure its the thermal overload, i was just a mostly concerened about the High pressure staying so high while the compressor is off. it just sits at 170 psi, The same psi its runs at. it was sitting at 170 psi for 10 minutes with the compressor off.

if it didn't have a txv the high side would equal right out and drop down quickly with a piston type (orofice) on the evap. i thought maybe the TXV is stuck closed

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Originally Posted by kurt854

all it has is a thermal overload (witch is internal) , or i would just bypass it and see if would stay running.

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You cannot bypass internal thermal overload.

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i dont have the amps or sperheat numbers now., but i think there all ok.

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You cannot service AC unit based on assumptions. You need to measure currents, pressures and temperatures.

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i am sure its the thermal overload,

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Based on what observation?

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i was just a mostly concerened about the High pressure staying so high while the compressor is off. it just sits at 170 psi, The same psi its runs at. it was sitting at 170 psi for 10 minutes with the compressor off.

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Wait few hours and see.

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i thought maybe the TXV is stuck closed

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If that is the case, then your suction pressure would be in vacuum.

Have you checked the thermal overload to see if it is open circuit?

Check the superheat.
If it's having a hard time starting up, check the start circuit. Also check the run capacitor.

If it won't start, then this has nothing to see whit superheat because it isn't running yet.
Replace once the starting capacitor or place a smaller cap parallel with the original one for some time and see if this goes better.
Starting relay (potential relay?) can also be faulty.

If starting system is fine, then you're compressor is almost retired :)

thanks peter, yes i tried a new capacitor and a BOOSTER capacitor but no help there. the thermal overload would just keep it from starting. but it was not hot or even warm. its a brand new unit doing this out of the box so i think the thermal overload is just acting up. just oredered a new compressor.

Check to make sure the voltage is within range while starting.

Whats the suction pressure at when the compressor is trying to start?

I think a big difference between the suction and discharge is what causes the problem with low starting torque compressors, a high discharge pressure and a high suction pressure wouldn't cause a problem.

If the system is not equalising after shutting off, try bleeding some refrigerant slowly between the high and low sides with your gauges when the system is off and see if this makes a difference. If it does it may be that the bleed port is blocked in the tev, check out the Sporlan valves site for an explanation on bleed port tevs.

http://sporlan.jandrewschoen.com/literature.shtm

Page 12 of bulletin 10-9 has a bit about off cycle pressure equalization/bleed ports.

Jon

Hi,
Is it a PSC or a CSR compressor motor starting system?

A PSC will only have one run capacitor, possibly 30 uF, and is low starting torque.

A CSR will have 2 separate capacitors, one run as above but also one start (100+ uF) as well as a Relay, probably potential type. This is high starting torque.

You can normally get the same compressor with both types of starting systems. It will be cheaper to buy a new set of electrics of the CSR type than a new compressor!
You could have an undervoltage problem on startup....i.e connected to a power ciruit that is underrated.

I've recently had a similar problem where the compressor was tight and poor circuit capacity gave voltage drop.

Also it could be advantageous to incorporate a delay timer in the control circuit.

Have you got a crankcase heater on unit? Was it left to heat up before starting.

Good luck.

You say you think it is off on thermal protection. This is an assumption that is not proven by measurements you report so far. Thermal protection will disable the compressor when the windings get overheated. They can "act up" but it's not often, especially when they are successful in resetting.

That leaves you with the important issue of diagnosing the cause of the problem. If you don't have flow of cold refrigerant to cool the windings, the overload will turn the compressor off after a while. Noncondensibles in the system might cause that too, since the thermal device may be located near the discharge path where noncondensibles cause high discharge temperatures. Your problem can be from a bad expansion device, a restriction in the system, restricted air flow through the condensor or evaporator or just a run cap short of value or leaking. Your problem can also be from a short between winding turns that causes winding heating and excessive current draw. If the system was not properly comissioned and has moisture in it, there could be copper plating in the bearings and parts that make the compressor "tight".

It is important that you make a diagnosis so you prevent an early failure of your repair. If you are right that your compressor failed, you want to know WHY. Otherwise, you can install a fresh compressor and burn it down too, or get short life span from it.

I will refer back to my earlier discussion about "tie wraps" used to fasten the expansion valve sensing bulb that caused my system to have a wrong superheat. I would not have found this installation error in the end of the system I was not replacing if I had not measured superheat. The new system was chargred "by the charts" and the system cooled well even with this fault. The brand new condenser unit would have failed young without this mistake and problem corrected.

I know guys here sound like they are being sticklers for getting information and measurements, but when you have a failed system, these measurements are your best hope of not visiting the issue again.