Dometic A/C question

[Full Monty]

I was just wondering if this is correct. When the rear unit is on and you turn the temperature up (to turn unit off) you can hear it turn off, But then it comes right back on. The fan is blowing and cold air is still coming out. Any advise would be appreciated.

[JRTJH]

When you turn a Brisk Air A/C off, the unit's fan will continue to run to "clear the ductwork" of cold air. This is a "design feature" to force all the "cooler air" into the cabin and to prevent cold air from pooling in the ductwork, potentially causing condensation.

If you listen carefully, when you "turn up the thermostat" or shut off the A/C at the thermostat, you can hear the compressor stop running. In some conditions (such as fan on HIGH speed) the fan will also stop, switch to LOW speed, and resume operating on LOW for a "timed period" to push that cold air out of the ductwork.

[NotyetMHCowner]

Our rear AC does the same thing: the compressor and fan will turn off, completely, then turn right back on within seconds. I had it looked at under warranty, but just like most of the problems, I was told "we couldn't duplicate the problem".

What concerns me is the compressor shutting off and back on so quickly without allowing the pressure to stabilize. And I can hear the difference between the fan and compressor.

[NotyetMHCowner]

Well, now I have a locked up compressor or bad capacitor. The condenser fan comes on but the compressor makes a very loud buzzing sound. We still have 2 days left at jekyll island with heat indexes above 110 and now down to one 13.5 AC. I am getting very disappointed with this camper and camping world for not listening to me. I told them I was afraid the short cycling would burn it up. I guess I get a whole new unit (unless it's just a capacitor).

[NotyetMHCowner]

It must be a bad capacitor because it started and ran for us last night. I shut it off before going to bed so we didn't wake up the campground again in the middle of the night. Just one more thing to add to the list on warranty work, again.

[Full Monty]

Now here is what it does. It will run and blow cold. It will go through its cycle and turn off. If you try to adjust the temperature up or down you get no response. You have to turn off then back on for it to respond. If you turn the thermstat to a higher temp while unit is running( to turn unit off) it will not turn off. No matter how high or low you adjust the thermostat.

[NotyetMHCowner]

That sounds like it could be a thermostat problem. Do you have 2 Ac's and if so do both operate the same?

[Jgkopp]

If digital wall t-stat it takes quite a few seconds to respond to your changes. Could also take up to 5 mins to respond to a cycle request so have some patience. Also as stated, if fan is in auto position you will hear fan stop and then start right back up when changing speed. As temp gets closer to set point the fan shifts to low speed from high. It sounds like the compressor shuts down but it is only the fan. All normal operation.

On the possible locked rotor you would hear the compressor making a loud hum and then hum will stop due to thermal overload tripping off. It will cool, reset and try again. One should check park voltage and I hope one is not trying to operate with extension cords in the shore power circuit. May have blown run cap if continues to fail to start. Could consider a OEM factory start kit after testing that the run cap is within spec.

John

[NotyetMHCowner]

We have a progressive industries EMS unit and it shows voltage good. I am not using an extension cord. We have turned it off each time before it has tripped. It is a very loud buzz kind of like a fire alarm buzzer in a commercial building. We tried a few times 2 nights ago and it started and ran fine but would not start last night at all even after about 20 tries. Warranty should take care of it.

[Jgkopp]

Good information. On your EMF unit are you able to see the voltage drop when this a/c is trying to start up? For the hech of it if possible try plugging into another spot and give the a/c another try.

We have a neighbor in our park in front of us, you could really hear his locked up compressor on a fairly new rig (a couple years old). I got up there and checked the run cap and it was good. It is a Coleman a/c with an LG compressor. If a start kit does not get it going he is going to have to replace the compressor.

[NotyetMHCowner]

I thought it was either a capacitor or compressor until I was able to get it going one last time. It ran for hours then, so I knew it was not the compressor. I shut it off at bed time, because I did not want it to cycle and get hung up in the middle of the night again. The next day, we could not get it started at all even after about 20-30 tries. My meter will not check capacitance, so I cant check it. It is under extended warranty so they will fix it anyway.

Ever since we have had it, I think it cycles the compressor too soon. Our front unit does not work that way. When it satisfies the temp, the compressor shuts off then after a minute or so the fan stops and the whole unit stays off until the temp rises a certain amount. Some of the time the rear AC works that way, but most of the time it will turn off, then right back on within 5-10 seconds and I can hear the compressor come on 5-10 seconds after that. That is called "short cycling" and will damage the compressor over time. I am afraid that is what may have caused my problem.

I can not see voltage drop at start up with my EMS but can see the voltage drop as the load increases as the monitor cycles through the different voltages and amp draws.

[NotyetMHCowner]

From what I have read about this dometic thermostat and rear AC is when running the AUTO, the rear AC has to shut off, then start again (within seconds) to a different fan speed. Each time the speed of the fan needs to change it does this. We have avoided burning it up again on the new AC by not using AUTO fan. We choose the fan speed ourselves according to how hot it is. Then the compressor will cycle on and off as it needs but the fan runs the whole time. Its gets tiring listening to the loud AC fan run all the time, but I don't know what else to do with it. The front AC works like it should with the same thermostat.

[texas-traveler]

on my other rig had the a/c would intermittently trip the breaker. Went to the extent of replacing the a/c unit, relay panel and t-stst. the new unit also started the same problem. To make a long story short, it turned out to be a bad breaker for the a/c. way we found it we removed shore power. reset breaker and measured resistance across reset breaker. was measuring 3 to 5 ohms.( causing major power loss, voltage drop and higher amp draw to compressor) should be only 0.1 ohms when reset. caused over amp condition when compressor would kick on or recycle.
also checked main breakers, they were resistive also. replaced them also. Replaced breakers with square D. better rating.

[texas-traveler]

Another problem with digital t-stat and newer control panel is ac voltage ripple ridding on the 12vdc control line. found mine had average of 500-700 mv of acv ripple. Caused by bad filter capacitor in power converter.
just another place to check.