AC Compressor short cycling

gaucoin1 · 09-12-2016, 11:56 AM

Hello! Looking for some advice or help on this. Main AC unit is short cycling. Checked power and was getting 122 volts on both legs of a 50 AMP site.

Had someone look at it and they said compressor was dead and the whole unit needs to be replaced.

Any thoughts? Anything else I can check before replacing this year. It is only 4 years old.

**Bama Rambler** · 09-12-2016, 06:00 PM

What is the brand and size of the A/C?

Explain what you mean by 'short cycling'?

Have you replaced the thermostat?

What have you tried in the way of troubleshooting?

How handy are you with electrical troubleshooting?

Toddupton · 09-12-2016, 06:06 PM

Short cycling is caused by either high pressure, low pressure or voltage problem. First step is to find which one of these it is. High pressure could be caused by a bad fan motor or blade or the coil could be plugged with cottonwood or the like or bad pressure switch. Low pressure (if your unit has one) is caused by low charge or bad pressure switch. Voltage could be a bad capacitor either start or run or wiring issue.

gaucoin1 · 09-13-2016, 09:21 AM

this is the 15k BTU domestic. I am not a good electrical troubleshooter. WE did check power in on both legs at the box and then in the camper and we were getting 122V on each leg of the 50amp.

the unit was working the weekend before and into the next weekend and started acting up on Sunday.

service guy came out ( i was not there and said the compressor was dead). we had the thermostat set on 72 and he lowered it to 55 with the same response.

the fan would run the compressor would kick on for a short period and then shut off.

How would i tell high pressure or low pressure in this scenario. You guys are great! thanks!

Toddupton · 09-13-2016, 10:19 AM

What kind of service guy came out? Was he an HVAC tech or a mobile RV tech? An RV tech will say the compressor is bad and will not do any troubleshooting at all. I would start by replacing the capacitors first since most likely you do not have the tools to test them. They are cheap and easy to replace assuming it is not under warranty.

Iggy · 09-13-2016, 10:33 AM

Do you have the fan set to AUTO?
If it is on low or high fan and AC the AC with turn on and off but fan will keep running.

**Bama Rambler** · 09-13-2016, 12:05 PM

Since you say that the compressor runs for a short period, I'd have to say that the compressor isn't dead.

I think I'd take Todd's advice and replace the capacitor(s) and see if that works.

V-Lite Fun · 09-13-2016, 02:10 PM

Not sure what short cycling is. Does it blow cool air? Our AC would come on and run a couple of minutes and shut off long before the trailer was cooled down. I discovered one vent was pointed at the thermostat. I changed its direction and it worked as it should. Sometimes it is simple things.

cmalberto · 09-13-2016, 02:19 PM

Quote:

Originally Posted by gaucoin1

this is the 15k BTU domestic. I am not a good electrical troubleshooter. WE did check power in on both legs at the box and then in the camper and we were getting 122V on each leg of the 50amp.

the unit was working the weekend before and into the next weekend and started acting up on Sunday.

service guy came out ( i was not there and said the compressor was dead). we had the thermostat set on 72 and he lowered it to 55 with the same response.

the fan would run the compressor would kick on for a short period and then shut off.

How would i tell high pressure or low pressure in this scenario. You guys are great! thanks!

Been there - done that - got the post card and now a new A/C.

So that is exactly how my A/C perils began back in May. What you can do temporarily is to test the OH Switch - it sits on top of the compressor. Looks like a jumper with a little round thing(y) in the middle - wish I had a picture of mine to show you - you can remove it it temporarily - the part costs about 10 bucks. May sure you unplug from shore before doing it.

If it works - you will get some extra life - I replace my OH switch after running a couple of days with out it. The following month the Compressor finally gave up.

Cost me a 75 dollar service call to ultimately replace the unit - they warned me this can be a sign the the compressor will probably go next and it finally did shortly there after.

Iwannacamp · 09-13-2016, 02:56 PM

I would not think these units have pressure switches. There are generally 2 safeties on small a/c units. There is a klixon type device on the common leg of the compressor and an internal overload inside the compressor. The klixon type will reset after a couple of minutes and the thermal overload could take hours. If the compressor starts over and over then you know the windings aren't bad. It would start too many times without tripping breaker.

If it runs several minutes and then stops for a few then stops again... Then I would look for a low voltage(stat) type problem...assuming it's cooling when running. Is the fan turning off at the same time? Then it always has to be cycling with temp. Put something over the stat and block the air, but you said you set it on 55?? It shouldn't cut off at that. Anyway cheap check.
I know the auto answer is crappy Dometic a/c. I think the year range is 2012 to June of 16 on 15k units.

Sent from my iPhone using Forest River Forums

Iggy · 09-13-2016, 04:05 PM

Quote:

Originally Posted by V-Lite Fun

Not sure what short cycling is. Does it blow cool air? Our AC would come on and run a couple of minutes and shut off long before the trailer was cooled down. I discovered one vent was pointed at the thermostat. I changed its direction and it worked as it should. Sometimes it is simple things.

Here you go.

Toddupton · 09-13-2016, 05:20 PM

Quote:

Originally Posted by Iggy

Here you go.

That touches on it but 9 times out of 10 that will have nothing to do with it.

**Flybob** · 09-13-2016, 05:24 PM

If it is hot and humid and you have a ducted unit, the coils an freeze up and need to thaw. The easiest solution is to use the quick dump opening on the main unit to reduce the temp and humidity. After the inside gets closer to where you want it, you can close the dump vent and use the vents.

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