Community Forums

Rook · 06-29-2012, 11:01 PM

This is a continuation of another thread located here:

http://www.irv2.com/forums/f258/roof...em-126084.html

You do not have to read the older thread to benefit from what I am going to say here. It will just help you understand what all I have been through lately.

I took my MH to an RV service place 30 miles north of where I live (60 mi RT) to have the new AC unit installed. The new Dometic AC unit, new control board for front unit, new 5-button Thermostat, and new control board for back unit and removing shroud from back unit and thorough cleaning.......$1384.00 out the door. Got back home about noon, BOTH AC's worked GREAT!! However, both AC's crapped out about 4 pm that day and were "kapoot" all evening. Turned off the thermostat and went to bed, pissed! Hot night....not much sleep. Took the MH back the next day for diagnostics and repair, early 8:AM, and low and behold everything worked again!! However, they replaced the front control board and put in a new 5-button thermoatat just as a precaution......everything worked great! Back home by 1:PM, very HOT day, 106 degrees......AND.....both AC's crapped out again about 4PM!! Double UGH!! @#$%^& So.....For the 3rd time, back to the RV service dealer the next day, 104 outside! Checked all the cables between the thermostat and front control unit....replaced all connectors, replaced the front control board for the 3RD time!!....turned on and it worked GREAT!! Ran generator and then sit on the parking lot for two hours and it just worked great! Back home.....started cooking my supper about 4:PM and right on schedule both AC's went "Kapoot". By now I am madder than jello. hotter than a stove top, and wondering if this is what "Jobe" was feeling! And .....by now, I am well acquainted with the service tech, Harold, and I have his home number......phoned him and "suprise" he is headed my way on Friday night to visit some friends and will come by to see if he can fix the problem!! He verified nothing working! Started measuring voltages......12 volts into the front control board varying all over the place.....10 volts, then 17 volts all the way up to 50 volts!!......make a loooooong story short......he then just casually mentioned, "it could be these florescent lights!!". I said what!!? He then said Coleman AC's have had a real problem with defective Florescent Lights screwing up the Thermostats......but he had never seen it on Dometic units. Well, he has now seen it!! It's now mid-night, I sit here cool and pleasant telling you about this unbelievable story!! Rook

Carl Bice · 06-30-2012, 04:33 AM

Very good information, I had never heard of it happening, but thanks to you and this site, I have now decided that I will go with LED's instead of florescent.

blackf3504dr · 06-30-2012, 04:34 AM

Strange ! Were you also sitting there in the dark ?

Carl Bice · 06-30-2012, 04:53 AM

Quote:

Originally Posted by blackf3504dr

Strange ! Were you also sitting there in the dark ?

I was wondering the same thing, lol

Rook · 06-30-2012, 06:03 AM

No, I have other lights.....it's only the bad fixture (Ballast transformer) that modulates the 12 volt buss with high frequency AC. Rook

HD4Mark · 06-30-2012, 06:13 AM

Sorry you had to go through all of that but thanks for some really good info. We have a Coleman unit and a couple of fluorescent lights so if it ever goes kapoot (I like that) we will try shutting them down first.

wa8yxm · 06-30-2012, 08:12 AM

Thought they still call it a "Ballast" when florcesent lights are run on 12vdc.

It is really an inverter. Just so you know.

How it hit the A/C with 50 volts, or for that matter even affected the voltage there, I do not understand.. Less some very cheap wiring was done on your house.

Mine the power to the A/C control comes off the main fuse block
So does the power for the lights.

But on a different wire. So this kind of thing should not happen.

SVTotem · 06-30-2012, 08:45 AM

I have heard of this referred to as "AC Ripple" and it has a similar affect on refrigerator controller boards. We went through three Norcold boards before finally running a dedicated 12v line.

PDR John · 06-30-2012, 11:04 PM

Quote:

Originally Posted by wa8yxm

Thought they still call it a "Ballast" when florcesent lights are run on 12vdc.

It is really an inverter. Just so you know.

How it hit the A/C with 50 volts, or for that matter even affected the voltage there, I do not understand.. Less some very cheap wiring was done on your house.

Mine the power to the A/C control comes off the main fuse block
So does the power for the lights.

But on a different wire. So this kind of thing should not happen.

It has the biggest effect on the 12v thermostat. On mine it happened while we were gone, reset the temp to 0. When we got home it was 53 in the RV, the cat was not happy.

Midniteoyl · 06-30-2012, 11:26 PM

Quote:

Originally Posted by SVTotem

I have heard of this referred to as "AC Ripple" and it has a similar affect on refrigerator controller boards. We went through three Norcold boards before finally running a dedicated 12v line.

Yep.. something like that.. It happens when cheap crap is used to build stuff, like florescent ballasts and control boards...

Sundancer268 · 07-01-2012, 05:50 AM

Quote:

Originally Posted by wa8yxm

Thought they still call it a "Ballast" when florcesent lights are run on 12vdc.
It is really an inverter. Just so you know.

No, they are still a Ballast on 12 Volts DC even if they are electronic instead of the old magnetic type originally used with AC. Agreed they take the DC voltage convert it to AC and change the frequency, now days to about 400Hz. They still are required (as the old magnetic ballasts) to raise the voltage high enough to strike the arc in the tube and then limit the current through the tube. The arc through the tube is just a short circuit through the ionized gas and current has to be limited to prolong the life of the fluorescent lamp and to prevent fuses from blowing in the system.
Short lamp life is one way you can tell that the ballast is going bad, also I know the lamp ballasts we use in our local Hospital have an internal fuse in the GE brand that will open when the ballast is defective. I have not torn open any of the other brands to check because the failed GE was the first electronic ballast I had ever seen and I was curious to see what was inside.

**CLIFFTALL** · 07-01-2012, 06:05 AM

This problem as it relates to Coleman has been discussed many times. There is a choke filter that can be simply plugged in to the thermostat. Here is a link to a thread where I posted a photo of it. http://www.irv2.com/forums/f54/rvcom...es-126229.html

38 Special · 07-01-2012, 08:29 AM

I had the exact thing happened to me. Two mobile service guys, over a grand spent. Found out myself, that is was the ballast in the bedroom flourscent fixture. Sure made for I hot two weeks at the beach. Ours, we would leave to go to the beach and the ACs would work (we cut out the light when we left). Come back, shower and change, ACs out, turned on the bedroom light. Another $50, and the problem was solved.

Hindsight said I should have realized it was tied to the light over the week we pained with this. However, I did not make the connection until it stopped while I still had my hand on the switch. Light off, 2 minutes (time delay), ACs came back on.

Rook · 07-01-2012, 09:24 AM

I am amazed that this "Florescent Light" problem is not more widely known among the RV service industry and the RV appliance industry. However, it does seem to have some awareness among the users of this site. I am very disturbed and astounded to have become the victim of this simple problem.....

This is what this little dittie has cost me........an extra $162.00 in diagnostics labor charge, plus 4, yes that's 4, extra trips of 60 miles in my MH to the service facility to try to fix the problem, plus 20 hours of my time, plus 4 days and nights of discomfort in record breaking heat and 4 days of high stress!

This is what Dometic says about the 12 volts input to the electronic control box:...
To check DC volts, first check the incoming DC volts between red (+) positive, and black (-—) negative, at the connections on the electronic control box on rooftop units; or at the connections at the electric box on basement units. Next check the output DC volts from the control box to the thermostat. This can be done by using a short telephone communications line. One end plugged into one of the RJ11 connectors on the control box and the other end plugged into a standard telephone jack. Next measure the DC volts between red (+) and black (-–). If volts are more at this check, AC ripple is on the incoming DC source. Be sure DC volts are less than 30. The control box has a filter within the circuitry to filter any AC ripple and will increase DC volts if AC ripple is present.

You can see that Demetic expects to sometimes have some "ripple" on the 12 volts input to the control box, even enough that when filtered it can increase the DC volts to the thermostat up to 30 volts! When you attempt to measure 12V DC with a digital voltmeter on the 20 volt range, you get an "over-range" indication of 1, indicating that AC is present and you immediately wonder if your meter is Kapoot! Increasing the DCV range does not give you a valid reading. Changing to the ACV mode may give a reading of 50-60 volts because it is 400 cycles, not the 50-60 cycles the meter is designed to measure. An Oscilloscope would show exactly what the problem is.

I would think that EVERY RV service facility would have this problem printed on the forehead of all Techs!! You can bet that I will never forget it!! Rook