Help! A/C only works when below 100°

[Espee]

Hopefully someone can help me diagnose…
Cooking here in Lone Pine CA at 105° this afternoon.
I know the cycles / behavior of this Dometic Brisk 2 Air conditioning unit (15k btu), so I think can articulate what it should / not be doing.
It starts normal operation but I hear the compressor drop out after about 5 minutes.
I hear the relay in the module send what I presume is a command to cycle the compressor a few minutes later but nothing happens and it just blows warm air until I shut it off for 15-20 min. Then we can repeat the cycle. Once temps drop below 100° it seems to consistently operate normally (compressor stays engaged), but not totally confident on that yet. Currently the compressor engaging sounds like a much softer start than I remember over the years of operation. I am leaning a capacitor on the edge of failure but would appreciate any other input to verify. I typically maintain a 22° return / supply differential and unit appears to be clean well maintained otherwise. This has been an intermittent issue for a number of months now…
Thanks
Jeff

[wapiticountry]

wa8yxm wrote:

prichardson wrote:
Ditto of Lou. Make sure the the condenser coil is clean.

.(My hands are xxl or xxxl depending on the brand of glove)

So what the women say is true: Big Hands....Big Dickies (the brand, not what the mind in the gutter people are thinking) .

[MrWizard]

ESPEE congrats, job well done ,
Nice to get the feedback on the results,
MANY TIMES people don't post back

[bucky]

^^^^^^^^^^^^^ It's rare anymore that someone comes on here with a well explained specific issue that gives the brains on that particular subject enough data to help.
Then the OP has the ability and the tools needed to follow the advice to a probable good result.
Rare indeed and kudos to all involved to this point. That's how this forum used to be.

[Espee]

Thanks for all the responses.
I have tried to follow up on everyones suggestions… other than calling out a tech for an intermittent issue, or just replacing the unit. 🙂

Voltage is above 110v when fan/comp are operating.
Current spike is about 4 amps for fan motor then settles at 2ish amps, and spiking about 26 amps for herm comp settling at 14ish amps from what my clamp on can catch. So running about 16.5a in the upper 90°’s here (within factory specs).
Fairly clean coils from visual inspection (better than my 4 ton at the house).
No ice buildup.

I had been looking everywhere for a replacement Positive thermal coefficient resistor (wsx-7) as suggested, but it was out of stock everywhere (dometic called it a motor starter, but said it had been discontinued). I finally found a coleman hard start kit with a capacitor that included the same PTCR wsx-7 replacement I was looking for at a parts house in Reno. It had a cap rated at 43-53 Mfd. vs my original cap that was rated 43-52 MFD, so I didnt swap it out just yet as my current ratings were still ok for now (IIRC, one Mfd higher on replacement specs is not an issue, so I will save it as a backup for now). I swapped out the PTCR and its running normal for now.
Now just need a few days over 100° to see if we got this fixed. FWIW I saved the old “thermistor” for further testing if I can find a diagnostic procedure for it…

[2oldman]

time2roll wrote:
Post the voltage in the RV and the amp draw on the A/C circuit.

Yes.. is the CG voltage ok?

[time2roll]

Post the voltage in the RV and the amp draw on the A/C circuit.

[Fulltimers]

Check to see if it is icing up.

[wa8yxm]

prichardson wrote:
Ditto of Lou. Make sure the the condenser coil is clean.

Double ditto

On most A/C's (Coleman is the exception) they BLOW air out from inside through the condenser so "Crud" builds up on the fan side of the condenser.
When this happens the system can not shed heat. it builds up. pressures go up and Click goes the breaker.

Colemans. (Air Xcel) Suck. So you see the crud on the outside (back)( of the condenser. Remove 4 bolts. lift cover, peal crud off replace cover 4 bolts. good to go.

Ohters it's like a dozen screws. then remove shroud, then you need to figure out how to remove inner cover over condenser (sometimes that's just a few more screws. other times you don't want to know) and if you have tiny hands (not) like I do remove the fan in order to do a proper cleaning....(My hands are xxl or xxxl depending on the brand of glove)

[jjrbus]

On top of most compressors is a high temperature coefficient resister or switch for most of us that senses temperature. Not pressure or amps . So is yours working right and doing its job protecting the system or is it failing? If I were you that is the first thing I would be looking at. Lots of info on the net on how to test.
And is your power source up to snuff, generator putting out right, power grid dropping when everyone has AC on and you are actually in brownout conditions?

[prichardson]

Ditto of Lou. Make sure the the condenser coil is clean.

[3_tons]

As I recall on my Coleman Mach 1, there is a high temp bi-metallic cut-out switch at one of the compressor terminals atop compressor…Sounds like a problem based on a certain pre-prescribed temperature…

3 tons

[LouLawrence]

Try cooling the whole thing down with some water from the hose. Also check to ensure there is no blockage of the outside cooling fins. Remove the top cover and check to ensure there is nothing blocking proper air flow as well.

[Seon]

I had a similar problem AC cooled fine but when ambient temp reached 100° it'd trip the breaker. Thinking the capacitor was failing, had it tested and it was okay. Being the unit was 10 yrs old just decided to replace with new. Best decision made.

[wildtoad]

My advice is to call a RV AC technician.