aircon suddenly turns off after 3 mins

[kafor1]

So i worked at a part time job maintenance crew at mcdonalds, and they ask me to try and repair the aircon

So the problem with the aircon is that after i turn it on it suddenly turns off after 3 minutes.

i tried testing the capacitor and the capacitor seems fine
i tried checking the breaker after it turned off (aircon). but the output of the breaker still has 220v and theres a circuit inside that has a led indicator. meaning it works but the fan is not running or aircon. sorry bad english
then i tried the contactor. during the period where the aircon runs, the contactor closed. after 3 mins the aircon turned off so the contactor open. i thought to myself. hey if i press the contactor (shorting it) it would probably run since its open. after i pressed it , it Sparks. but the aircon doesn't run.


figure A (inside of the aircon)
figure B ( larger view)
figure c (aircon)
figure D ( outside view of aircon)

Thank you and GODBLESS

[Gazucha]

Are you sure it has refrigerant?

[kafor1]

Are you sure it has refrigerant?

im not sure, ill take a look at it again tomorrow

[Gazucha]

Not sure that 3 minutes is enough time, but check the pipes where they enter the compressor when you turn the system on.

In a healthy system the smaller pipe ' sweats'... If it starts to freeze, then you need more gas. 

Which then begs the questions, "why?" and "is there a leak?"

[kafor1]

Not sure that 3 minutes is enough time, but check the pipes where they enter the compressor when you turn the system on.

In a healthy system the smaller pipe ' sweats'... If it starts to freeze, then you need more gas. 

Which then begs the questions, "why?" and "is there a leak?"

i see, how is that related to suddenly turning off?
ill also take a look at that tomorrow

[Gazucha]

They are designed to turn off with low refrigerant

Do you have a manifold?

[kafor1]

yes

[maginnovision]

What about the AC turns off? The condenser fan, the evap blower, the compressor? All of them? Does the compressor get hot? Do the lines change temp at all during those three minutes(check at the compressor)? Have you put a clamp and see if everything is pulling the right amount of current, or any current? Did you inspect all the electrical connections, any burning? Seems like you haven't done much other than take pictures and press a switch?

[Mechatrommer]

after 3 mins the aircon turned off so the contactor open. i thought to myself. hey if i press the contactor (shorting it) it would probably run since its open. after i pressed it , it Sparks. but the aircon doesn't run.

dont do that. mcu shuts it off because something happened that it thinks the aircon supposed to be turned off. if you try to outsmart the mcu without having a clear idea of what you are doing, you may burn something and make it worse.

Do you have a manifold?

yes

next question is, do you have refill gas tank? in case refrigerant low? if no, you may want to call certified tech anyway. btw you can search youtube for refill/pressure check guide, for example...

[jmelson]

In a healthy system the smaller pipe ' sweats'... If it starts to freeze, then you need more gas. 

Actually, that would be the LARGER pipe, the vapor return line.  If it ices up, that is a sure indication of low refrigerant.
Also, the small (liquid) line should get hot.  If it doesn't, that is a sure indication there is little refrigerant in the system.
Many systems have low-side and high-side safety controls that shut it off if either the high-side pressure goes too high, or the low-side goes too low.
Some systems have these latch, so you need to press a button to reset them.  Seems like this system does not have that latching feature.
Some systems may also have a sensor to detect iced-up evaporator coils, blocked air filters or broken fan belts.  That would be the air handler unit.

Jon

[Gregg]

3 minutes is approximately the time needed for a unit to shut down because of high compressor output pressure (often called high head pressure).  This can be because the condenser fan is not working, the condenser is clogged with dirt and grease, the thermostatic expansion valve is sticking closed or a filter between the compressor and expansion valve is plugged up.
Low refrigerant is often accompanied by the evaporator icing.

[james_s]

That's what I was going to suggest, often there's a pressure switch on the liquid line which will shut off the system if the head pressure is excessive. I would look to see if it has one of these and measure the voltage across it to determine whether it is activating. Once you work out what mechanism is causing the shutdown you'll be in a better position to determine why that mechanism is activating.

[BradC]

In a healthy system the smaller pipe ' sweats'... If it starts to freeze, then you need more gas. 

Actually, that would be the LARGER pipe, the vapor return line.  If it ices up, that is a sure indication of low refrigerant.
Also, the small (liquid) line should get hot.  If it doesn't, that is a sure indication there is little refrigerant in the system.

If the system has the expansion valve in the evaporator, then the liquid line leaving the condenser will be warm. If the expansion device is in the condenser then it will be cold. Plenty of examples of both in air conditioning.

Regardless of that, a universal truth is if you have frost or ice on the suction line the unit is either over charged or has a problem (such as a dead evaporator fan) which is causing a catastrophically low load and causing liquid floodback. Liquid floodback is not good and even on systems with accumulators good practice dictates sufficient superheat to prevent it.

A stalled evaporator fan and a txv system will cause excessively low low-side pressure, and a stalled condenser fan will cause excessive high side-pressure. Most (better than cheap domestic) systems have both low and high side cut outs. The low side cutout prevents the system killing the compressor with insufficient refrigerant, and the high side cutout prevents the system blowing itself to bits with high pressure.

As the others have said, check your fans (both of them).

[james_s]

The only time I've ever seen an expansion valve in the condenser is in a heat pump in which case there are two expansion valves and the one in the outdoor unit is only used when that coil is operating as the evaporator at the time. I have only worked with domestic systems though, perhaps large commercial ones work differently?

Either way if you look at the compressor itself, the small line is the liquid line and will be hot, and the big suction line will be cold but should not be iced up.

[kafor1]

Update: Looks like it was a refrigerant problem after all, but instead of low or no refrigerant, too much refrigerant was in there that caused probably high pressure. thank you everyone for your help. and sorry for the late update