AC does not run with generator

[n4248z]

Concerning 2004 Monaco LaPalma. Front AC unit does not run when using generator. It works on shore power. Rear AC runs on both generator and on shore power. Suggestions ? Thanks.

[Dr4Film]

Maybe check your ATS (auto transfer switch) to make sure power is being transferred to both legs of your coach when the generator is running. Each AC runs on one 50 amp leg of power when hooked to shore power and the same would be true for the generator.

Are there other 120 VAC outlets not working too?

Edited December 29, 2019 by Dr4Film

[Bob Nodine]

37 minutes ago, Dr4Film said:

Maybe check your ATS (auto transfer switch) to make sure power is being transferred to both legs of your coach when the generator is running. Each AC runs on one 50 amp leg of power when hooked to shore power and the same would be true for the generator.

Are there other 120 VAC outlets not working too?

To expand on what Richard is pointing out, on a 50 amp coach the shore power has two legs and the generator had two legs. Because the air conditioners are high current devices the manufacturer will divide them between the two legs (phases) of power. The transfer switch is responsible for switching power between the shore power connection and the generator. It must switch both phases so at least two double pole - double throw sets of contacts are used for this. It is possible that one of the contacts is not switching from shore to generator and that air conditioner is only receiving power when you are connected to shore power. Another possibility is that the connection for one of the generator phases is broken or has a high resistance at one of the terminal lugs on the transfer switch. The transfer switch and the AC power distribution panel should have all the terminal screws tightened once a year. I put this in a calendar reminder and go thru all the terminals when the event comes up. This can prevent you from having a connection overheat and cause a failure or even a fire.  The first place to look is the transfer switch. If you are not comfortable doing this get someone who is and check it out. With a multimeter on the AC range you can test the power from the generator and the shore connection at this single location. While plugged into shore power the output of the transfer switch should show a reading of about 120 VAC on each of the phases to ground. Since both units work on shore power this condition must be true. Once you have verified this turn on the generator and again test the output of the transfer switch. If one of the legs is missing you have your answer.  Start working back from there to the other side of the transfer switch. If both legs from the generator are live to the input of the transfer switch then you must have a bad transfer switch. If not then your problem is either in the generator itself or the wiring from the generator.

 

Edited December 29, 2019 by Bob Nodine

[Steven P]

If you still have the IOTA transfer switch, you may want to consider replacing it due to the fire risk hazard.  After reading about all the failures, I swapped mine out and have been happy w the replacement. 

[n4248z]

What transfer switch  replaces  50 amp IOTA ? 

[Steven P]

2 hours ago, n4248z said:

What transfer switch  replaces  50 amp IOTA ? 

The Esco lpt50brd does.  If you look at the pic, you can see the model on the right side. That is the one I installed.  About $175 on Amazon.

[jacwjames]

One other thing to try is to flip the generator breaker Off and then back ON.  This is a single through double breaker, it is possible that one side tripped.  I've also read that the breaker can fail so you might check it's output to make sure it is passing power.