Carrier A/C cuts out

[jwilson12]

Can anybody help me?
Carrier 38XQ- 050 3ph reverse cycle Aircon has 5 minute delay start, but then it cuts in and cuts out every 5 minutes when running on cooling. the R22 refridgerant was recently replaced because of a leaking schrader valve.

[dogma]

Is there a blockage in the system?

[jwilson12]

Dont think so,it runs for longer during the night how do i find out if it has a leak thanks

[jwilson12]

that should have read blockage not leak! Duh

[dogma]

that should have read blockage not leak! Duh


He fixed the leak.....didn't he??????



I have a piece of suction line where they fixed a leak and the system was doing the same thing. They resticted the line down to the thickness of a pencil lead.

The system did the same as this carrier in question.

[dogma]

Check the indoor fan coils....... Is there more than one circuit on the coil. Is one of them blocked?

[jwilson12]

Have checked the coils all looks fine. The schrader valve cap that was leaking and replaced was in the indoor fan unit.Will the continual stopping and starting of the compressor affect the unit Adelaide is going through a heatwave at the moment and is expected to stay around 38 degrees celcius for the forth comming week .

[paul_h]

My guess is tripping on HP or LP, or high current draw.
Is the outdoor fan running?
Could be over charged or under charged with refrigerant or have compressor or reversing valve fault.
But thats all just guessing, but it's enough to tell me you need a fridgey to look at it. I'd start by calling back the guy who played with it before as it could be a refrigerant quantity issue, as I don't think there's anything you can do unless it's a blocked condenser or fan fault

[ruvy frank]

i think its under charge try to add on sum gas. but it might also be a case of moisture in the system. when it lost its charge wasnt the unit contaminated????

[nike123]

i think its under charge try to add on sum gas. but it might also be a case of moisture in the system. when it lost its charge wasnt the unit contaminated????
How could you tell that is undercharged without knowing superheat and subcooling? That is guessing like weather forecast in stone age.:eek:
You maybe could say that it trips on HP/LP switch but that doesn't necessary mean that is undercharged.

[Electrocoolman]

Could be overcharge and cutting out on HP as condenser has lost SC or Condenser needs a clean.

It runs longer at night when outdoor ambient is lower.

BTW Adelaide's a lovely place....was there in '76 - '78.
Glenelg and the tram....is it still running?

[jwilson12]

Thanks for your suggestions I'm from glasgow came here in 1972 the old trams only run on the week end they have replaced them with new ones from Germany and guess what the air cons in them cant keep up to our temperature.they have also extended the tram lines down to North tce
my air con cuts in and out every 5 min while the fan is on contiuous i have turned it to auto and it appears to run for about 15 min and then cuts out for about 5 mins is this relevant .is there somewhere i could get a manual for this air con it was built in 1991. Cheers

[dogma]

Bro, It'd be cheaper and easier just to get a qualified mech to look at it. If It has lost refrigerant on the low side there may be non condensables in the system.

Recover, Evacuate, Pressureise o/night with nitrogen, Rechage, Clean all the coils and filters then test again.

[frank]

If It has lost refrigerant on the low side there may be non condensables in the system.
How do you work that one out then Dogma?
I would expect that the system would have to run in a vacuum to draw in non-condensibles, but we haven't been given any running pressures or currents so far.

Without a lot more information on this system, we are all just guessing.

[dogma]

Without a lot more information on this system, we are all just guessing.


True talk Frank. :)

[The MG Pony]

when odd intermitent things start, do an audit!

Check all coils for cleanliness shine a flash light through to make sure! Check air temps on evap and condencer, be shure flow is smooth.

Check running pressurs suction & discharge, messure SH,SC. Check fans for bering function and eas of movement, current draw of fans and compressor each indavidualy, then sum and compar to the units lable.

With all this data the fualt will jump out and bit you whilst wigling!

[jwilson12]

when odd intermitent things start, do an audit!

Check all coils for cleanliness shine a flash light through to make sure! Check air temps on evap and condencer, be shure flow is smooth.

Check running pressurs suction & discharge, messure SH,SC. Check fans for bering function and eas of movement, current draw of fans and compressor each indavidualy, then sum and compar to the units lable.

With all this data the fualt will jump out and bit you whilst wigling!
Sounds good advice but wwhat do SH & SC stand for. Will the continual starting and stopping every 5mins affect the motor compressor Adelaide has just had 12 straight day of over 35 degrees cel. and is going to last for at least another 3days ca'nt get a repair guy for weeks

[Electrocoolman]

Hi,
SH - superheat
SC - subcooling

These are refrigeration terms that you find a lot about on this forum if you use the search facility. These can be used to indicate how a system is operating.

No...its certainly NOT a good idea to allow your compressor to constantly switch on and off....you will need a new compressor very shortly if you allow this.

You still not have given us an indication if you have checked the fans and the coils.

Does the outside fan run when the compressor runs?
If you have access to an aircompressor and blowgun have you tried blowing out the fins of the outside unit.

One quick test is to examine the pipes where they connect to the outside unit...the larger one should be cool, possibly wet, but not icy like the small one.

Regards.

[jwilson12]

Hi,
SH - superheat
SC - subcooling

These are refrigeration terms that you find a lot about on this forum if you use the search facility. These can be used to indicate how a system is operating.

No...its certainly NOT a good idea to allow your compressor to constantly switch on and off....you will need a new compressor very shortly if you allow this.

You still not have given us an indication if you have checked the fans and the coils.

Does the outside fan run when the compressor runs?
If you have access to an aircompressor and blowgun have you tried blowing out the fins of the outside unit.

One quick test is to examine the pipes where they connect to the outside unit...the larger one should be cool, possibly wet, but not icy like the small one.

Regards.
Both of the fans run ok when the unit is running the indoor fan runs continuous or auto i keep it in cont. the outdoor fan starts up and stops every 5mins or so and runs much longer in the early morning or evening when its cooler .The large insulated pipe is cold to the touch but not damp The small pipe is hot to touch when the unit is running but cools when stopped. Both indoor and outdoor fans have overload protection.

[powell]

jwilson12,

It's time for you to call in a HVAC technician to check this system out. I see in your profile that you are a builder so you should have someone available.

It's going to cost you in the long run if you don't. ;)

[Electrocoolman]

Hi there,
The small pipe is hot...how hot?...too hot to hold?

The fact that its warm/hot suggests that expansion device is on the indoor unit, but will need to check that it is.....(Perhaps someone else who knows these units could confirm).
The symptoms still suggest that it is stopping on a protection device....probably the high pressure switch, but we have to find what is causing the high pressure switch to trip.

One reason you can get a higher than normal pressure is if you simply cannot 'get rid of the heat'....so is the condenser clean all over its surface AND can you see through its fins. (see my suggestion above about blowing through with compressed air).

Is the outside fan motor failing....I think that it probably has an internal thermal cutout.....for this one, you need to see if the fan stops BEFORE the compressor does, or at the same time.

The fact that you say the unit runs longer when it is cooler outside... at night / early morning suggests this approach to the problem.

The repair and recharge that you had done could be significant as the guy could have overcharged the system with refrigerant.....this would have the effect of reducing the effective condenser surface area so that it cannot get rid of the heat. GET HIM BACK!!?? (or someone else for a second verdict!)

All these are possibles and will give you a HOT small pipe (assuming that your expansion device is not in the outdoor unit)

As Powell suggests, you are going to have to get someone in.

One final thought....where is the outdoor unit situated?...Is it sitting in full sun or shade? What about erecting some shade without restricting the airflow. Also can the hot air escape?.....you haven't got a problem with air recirculating....e.g. its pulling in its own hot air? A lot of plants that have grown too close?

Are these units squat box or dustbin shaped with the fan discharging from the top? Maybe a sheet of thin ply with a hole for the fan to fit through would be effective?

[jwilson12]

Hi there,
The small pipe is hot...how hot?...too hot to hold?

The fact that its warm/hot suggests that expansion device is on the indoor unit, but will need to check that it is.....(Perhaps someone else who knows these units could confirm).
The symptoms still suggest that it is stopping on a protection device....probably the high pressure switch, but we have to find what is causing the high pressure switch to trip.

One reason you can get a higher than normal pressure is if you simply cannot 'get rid of the heat'....so is the condenser clean all over its surface AND can you see through its fins. (see my suggestion above about blowing through with compressed air).

Is the outside fan motor failing....I think that it probably has an internal thermal cutout.....for this one, you need to see if the fan stops BEFORE the compressor does, or at the same time.

The fact that you say the unit runs longer when it is cooler outside... at night / early morning suggests this approach to the problem.

The repair and recharge that you had done could be significant as the guy could have overcharged the system with refrigerant.....this would have the effect of reducing the effective condenser surface area so that it cannot get rid of the heat. GET HIM BACK!!?? (or someone else for a second verdict!)

All these are possibles and will give you a HOT small pipe (assuming that your expansion device is not in the outdoor unit)

As Powell suggests, you are going to have to get someone in.

One final thought....where is the outdoor unit situated?...Is it sitting in full sun or shade? What about erecting some shade without restricting the airflow. Also can the hot air escape?.....you haven't got a problem with air recirculating....e.g. its pulling in its own hot air? A lot of plants that have grown too close?

Are these units squat box or dustbin shaped with the fan discharging from the top? Maybe a sheet of thin ply with a hole for the fan to fit through would be effective?
Good call about the unit pulling in its own heat it did have a lot of downdraught due to hot air not escaping quick enough.When the unit was first installed it had a vented roof installed above but in the ensuing years more roof area from verandas filled in the areas around which probably prevented hot air escaping .I removed the roof directly above and noticed an immeadiate difference.but guess what the hot weather has gone for the time being and its a pleasant 24 celcius Thanks for all your help this is a great site for professionals and the public to have access to and being scottish i was'nt to happy about paying an technician $80 per hour if they could'nt find the problem. once again thanks and lang may your lum reek

[Electrocoolman]

Great to hear that we've helped to solve your problem.

I must revisit Aus and Adelaide one of these days. Spent 3 years there '76 - '78. Good times.