AC shuts off after only running a few minutes

[LongWeekends]

I have a 2009 Monaco Camelot DSQ. It is the 42' model with 3 AC's on the roof. When I turn them on they only run a few minutes and then shut off. The thermostat goes blank. After 5 minutes or so they kick back on, the thermostat's screen comes back and all is normal. Then they shut off, etc.

What I know - it happens with both 50amp service and gen power.
Nothing else in the coach seems to be affected.
The EMS recognizes 50amp or gen power and shows uninterrupted power to the AC(and everything else) even when the AC units shut down.
All three units shut down and fire back up at the same time
We replaced the thermostat and the problem remained exactly the same.

EDIT FOR MORE INFO -
Rear AC and middle AC run perfectly when they are running solo or together.
Front AC cuts out running solo and/or kills everything when running with the other units.

So...the problem is the front AC unit.

Where do I look next?

Thanks in advance!

[LongWeekends]

LongWeekends wrote:
I have a couple of questions...what is the easiest way to determine which of the pigtails are for which unit? Is it just trial and error?

So I am back to no AC, same issue....no 12V to the thermostat. I replaced the connectors on the wire that runs from the thermostat to the front AC unit. I checked the wiring and I have continuity from ONE plug at the AC(pictured above) to the thermostat. Yellow at AC is yellow at the thermostat, red is red etc. I think that is correct. I installed the new connectors wired exactly as the old ones.

Questions: 1 - Is it correct, yellow at AC is yellow at thermostat etc? Seems that it should be but you never know.

2 - Should I have continuity with BOTH of the pigtails pictured above to the thermostat or just one?

[Mr_Mark1]

Doug, for you to take the time and read through these posts and help people is just amazing and fantastic.

Similar to the OP, I had an issue with our roof airs on the '08 Dynasty. Come to find out, the dip switches were set wrong from the factory which made the front and middle air come on at the same time from the thermostat. If I was connected to 30 amp shore power, this caused the shore power breaker to flip.

I found out that each roof air has dip switches as does the thermostat.

Safe travels,
MM.

[dougrainer]

LongWeekends wrote:
A quick update. Thanks for your help! I unplugged each black and gray wire at the front AC unit and cleaned the connectors on all sides. The AC has been cycling off and on perfectly all day since then. I'm not going to jinx myself and say it is fixed but it is working properly for now.

Thanks for the help. I would have never gone down that path and figured it out!

IF you saw corrosion on the plugs, cleaning will not do for a long term fix. Replace those modular plugs if they are corroded. BTW, that phone type cable is NOT a Phone cable. It is called a communication cable and the plugs are wired BACKWARDS from a phone cable. You cannot use a phone cable with plugs already on the cable. Doug

[LongWeekends]

A quick update. Thanks for your help! I unplugged each black and gray wire at the front AC unit and cleaned the connectors on all sides. The AC has been cycling off and on perfectly all day since then. I'm not going to jinx myself and say it is fixed but it is working properly for now.

Thanks for the help. I would have never gone down that path and figured it out!

[LongWeekends]

dougrainer wrote:


Trial and error on which phone cable is which. easy to do tho. unplug one--if the wall tstat goes dead that is the tstat wire. if not thast wire feeds the middle ac. Now, that plug is the remote sensor plug which you do NOT use. Your wall tstat is the temp sensor for that AC. The Middle and Rear units will have that wire connected to a wall temp sensor. What you have exposed, is exactly where the corrosion usually is. Odds are you have a defective cable cut or shorted. The BLACK phone cables connect to the Circuit board, the gray phone cables go to the Tstat or the middle AC. Doug

I don't know how you know these systems so well but I'm glad you do! Replacing the cable...can I tie it on one end and pull through or is it part of a bigger harness?

[dougrainer]

LongWeekends wrote:
I have a couple of questions...what is the easiest way to determine which of the pigtails are for which unit? Is it just trial and error?

Where do you typically find the corrosion? On the grey wire connector? Black? Both?

Dare I ask if it IS a bad cable, can I simply tie a new one to the old and pull it through or is it part of a big harness?

Finally, any idea what the unused plug that is hanging down is for?

Trial and error on which phone cable is which. easy to do tho. unplug one--if the wall tstat goes dead that is the tstat wire. if not thast wire feeds the middle ac. Now, that plug is the remote sensor plug which you do NOT use. Your wall tstat is the temp sensor for that AC. The Middle and Rear units will have that wire connected to a wall temp sensor. What you have exposed, is exactly where the corrosion usually is. Odds are you have a defective cable cut or shorted. The BLACK phone cables connect to the Circuit board, the gray phone cables go to the Tstat or the middle AC. Doug

[LongWeekends]

I have a couple of questions...what is the easiest way to determine which of the pigtails are for which unit? Is it just trial and error?

Where do you typically find the corrosion? On the grey wire connector? Black? Both?

Dare I ask if it IS a bad cable, can I simply tie a new one to the old and pull it through or is it part of a big harness?

Finally, any idea what the unused plug that is hanging down is for?

[LongWeekends]

dougrainer wrote:
Your Tstat should be controlled by the front AC control board. There are 2 power 12 volt wires to that control board. Make sure you have 12 volts positive and negative on the RED and BLACK wire feeding the front control board. This power wire set controls ALL functions of all 3 control boards. The 2nd AC control board is connected to the front and the 3rd control board to the Middle(2nd) by a phone type communication cable. So, your problem is either the Front AC control board or the telephone type communication cable between the Wall Tstat and the front Control board. It is extremely rare for the control board to be at fault on these type problems. At the front AC, you have a harness that has 2 phone type connections on 2 pigtails. Those pigtails are black. The wires running to the middle AC and the wall tstat will either be white or gray. Check the connections on the phone type modular plugs, disconnect them and look for corrosion. Your year and brand should have lo profile Penguin models. These are susceptible to excess humidity where these wires are and cause corrosion. The fix if you find rust/corrosion on the modular plugs is to cut the modular plugs OFF and install new modular plugs. If there is NO corrosion then the problem will be a defective phone type cable from any off the AC units and the wall Tstat. ONE shorted cable in any of these cables can cause a problem. The usual test is to take the wall tstat up to the front AC Modular cable connections and plug it directly into the front AC board with the Middle supply cable disconnected at the front AC and see if the front functions. If it does, you then leave the 2nd cable disconnected and reconnect the wall cable at the front board and reconnect the tstat at the wall and see if it still functions correctly. If it DOES your problem is isolated to the 2 rear AC unit control cables. If it does NOT, then your problem is between the front AC and the wall tstat on that cable. Doug

Thanks Doug. I haven't dug into any of it to the level you described and you gave a lot of info! I'll take some time to work through your response and see what I can find.

[Yaj]

Nice reply Doug! Your trouble shooting tips have helped me in the past, and this one is priceless!

[LongWeekends]

Thanks for the input. I edited the first post to include new info.

[dougrainer]

Your Tstat should be controlled by the front AC control board. There are 2 power 12 volt wires to that control board. Make sure you have 12 volts positive and negative on the RED and BLACK wire feeding the front control board. This power wire set controls ALL functions of all 3 control boards. The 2nd AC control board is connected to the front and the 3rd control board to the Middle(2nd) by a phone type communication cable. So, your problem is either the Front AC control board or the telephone type communication cable between the Wall Tstat and the front Control board. It is extremely rare for the control board to be at fault on these type problems. At the front AC, you have a harness that has 2 phone type connections on 2 pigtails. Those pigtails are black. The wires running to the middle AC and the wall tstat will either be white or gray. Check the connections on the phone type modular plugs, disconnect them and look for corrosion. Your year and brand should have lo profile Penguin models. These are susceptible to excess humidity where these wires are and cause corrosion. The fix if you find rust/corrosion on the modular plugs is to cut the modular plugs OFF and install new modular plugs. If there is NO corrosion then the problem will be a defective phone type cable from any off the AC units and the wall Tstat. ONE shorted cable in any of these cables can cause a problem. The usual test is to take the wall tstat up to the front AC Modular cable connections and plug it directly into the front AC board with the Middle supply cable disconnected at the front AC and see if the front functions. If it does, you then leave the 2nd cable disconnected and reconnect the wall cable at the front board and reconnect the tstat at the wall and see if it still functions correctly. If it DOES your problem is isolated to the 2 rear AC unit control cables. If it does NOT, then your problem is between the front AC and the wall tstat on that cable. Doug

[Prostar6]

Your thermostat is powered with 12v DC.
Had the same type of problem on my country coach it was a bad connection in the wiring harness going to the thermostat. My thermostat would go blank just like yours when I had several lights in use connected to the same harness. It could be a loose ground wire. Mine turned out to be a harness running next to the refrigerator and the heat had caused the connection to fail.