Intermittent Roof AC when driving

mrschwarz · 06-23-2011, 08:02 PM

About a year ago, I removed the kitchen vent and installed a 13K BTU rooftop AC in its place. The 24K BTU basement just wasn't cutting it in the 'mild' Texas summers. I wired it into the same circuit as the engine block heater, figuring that the engine won't freeze on the same day that the main AC unit won't keep up. It works great when stationary. The problem is when I am driving. Sometimes, when I hit an expansion joint on a bridge or a bump in the road just right, the unit will quit for a minute or two. It will then come back on and run for a couple of more minutes until I hit another bump. Every now and then it will pop the breaker, probably from the high head pressure due to short cycling. All I could figure is there is an intermittent connection that is opening up due to vibration.

I connected an extension cord to the engine heater which is on the same circuit. I plugged a drop light into it. Every time the AC went off, the drop light went off, too. While we were driving, we paid attention to how the problem was happening. Our observations: For the first hour or so, the AC didn't quit. Then, it quit once. The light went out for about 15 seconds and came back on again. After about 15 minutes, it went out again for about 15 seconds. After is came back on, it went out about a minute later and stayed off for about 5 seconds, came back on for about 20 seconds and went out for about 5 seconds again. This pattern repeated itself until we reached our destination.

On a hunch and at someone else’s suggestion, I swapped the leads for the shore power cable and generator at the transfer switch. This made the switch shore power priority and the generator was the default with the coil not energized. I drove from Sherman, TX to Little Rock, AR with all of the air conditioners running. I had my test light connected and for the 5 1/2 hour ride, it didn't blink once. This definitively identified the problem as the transfer switch and I think it has been faulty since I got the coach.

I called Winnebago and they agreed with my diagnosis that there was a problem with the transfer switch. Since the switch has a two year warranty, the rep recommended that I call Parallax. I did and spoke with a tech support rep there. His response was that their transfer switches are not designed to be powered while driving the coach. Because they are generator priority switches, when the generator is running, the contacts are held together with the relay. According to Parallax, there is no way they can design a relay that will remain closed during all kinds of road conditions. They won't replace it and cannot confirm that a replacement switch won't have the same problem, which they said exceeds their design requirements.

When I called Winnebago back, the rep was surprised by Parallax's response. He suggested that if this was common with their switches, he would have heard about it. I asked for a recommendation for a switch that was intended to be used while driving and he told me that Winnebago only uses Parallax switches. He suggested that I replace the switch, but I have a real problem with that. Why would I buy another transfer switch that the manufacturer says shouldn't be used. If it does the same thing, I will be the proud owner of two shoddy switches!

Apparently, Winnebago is installing transfer switches that are not intended to be energized while the coach is under way. I don't recall reading this in their manual and I don't think the guy that did the predelivery inspection mentioned that I should use the generator while moving, like I have done with my other two motor homes.

I have written an email to Parallax and copied Winnebago asking them to confirm what I was told. If this is true, everyone with a Winnebago coach should look into this and make sure you're not encountering the same problem. The only reason I know about it is because I added a roof air conditioner and could hear when it quit. With only basement air and road noise, there is no way most people would be aware that it was occurring. Constantly cycling the compressor(s) on and off puts an awful lot of wear and tear on them. If Winnebago doesn't recommend to not use generators while under way, should they be on the hook for electrical system damage that is caused by this?

I don't know about you, but to me this is a BIG DEAL! I live in Texas and if I can't run the generator on the road, Winnebago needs to put a whole lot more resources in the dash air. When it's 100 degrees out, a handful of vents on the front isn't going to cut it. For now, I am leaving the switch wired backwards so it works while I am driving. I can live with the shore power priority.

I got a voicemail from customer relations Winnebago after I sent them a copy of the email I sent to Parallax. They confirmed that Parallax's official position is that the transfer switch should not be used energized while driving because it is not designed to do so. He reiterated that this was the first time he had heard of this and recommended that I replace the switch, thinking that it is a faulty switch. He was also curious what Parallax's response to me would be. I haven't received one from them, yet.

Sorry for the length of this post. What do you think?

RJay · 06-23-2011, 08:37 PM

Michael,
Thank you for a well thought out post. From the amount of problems I've seen with transfer switches here on the forum your post confirms two suspicions I've had for quite a while. The force used to maintain connection between the contacts is low, and the transfer switch should not be used to switch loads greater 5 or 6 amps.

I agree with you about not replacing the transfer switch with another Parallax switch. You could always look into a 50 amp Iota transfer switch or some other brand.

"007" · 06-23-2011, 09:05 PM

I agree with RJay I would replace with other MFG.
I have never had this problem on any of my coach's with the Iota ST's.
Sounds like basement AC's or roof top will have a problem with the ST's Winn is using.
Your post is very good and Winn should look into it.

Harry B · 06-23-2011, 09:21 PM

What is the impact on the basement AC? I run the basement AC often while traveling and have not seen this problem. The basement AC is also powered through the transfer switch. Something doesn't make sense based on what you are being told.

ernieh · 06-24-2011, 12:49 AM

Quote:

Originally Posted by Harry B

What is the impact on the basement AC? I run the basement AC often while traveling and have not seen this problem. The basement AC is also powered through the transfer switch. Something doesn't make sense based on what you are being told.

Quote X2

doc · 06-24-2011, 09:28 AM

We had an issue with a loose screw attaching the wire to a breaker in the breaker box. Might take a look and make sure it/they are tight. Just have to pull the cover off and pop the breakers out. Oh yeah, make sure the power is off.

tomsm · 06-24-2011, 09:56 AM

Michael,

Well written post. I think I must disagree in one area though. In hot weather we always run the generator and basement air - keeps our 36' coach very comfortable. I'm quite sure I would be aware if the basement air shut off. First, the restart delay keeps it off for several (3?) minutes and the cabin would start to warm up quickly. Second, there is a vent almost right over my head that constantly blows beautiful cool air on me - I'm sure I would miss that immediately. And lastly, I'm almost certain that I would notice the change in generator sound. I can definitely hear the generator even with road noise and there would be a big change in pitch when going from over 20A to 0A.

Your forum info page shows that you have a 32' Meridian. Is that still true? If so, I'm very surprised that you needed the extra cooling. We've used ours all over TX, NM, AZ, UT, NV, and live in FL and I've never had a problem keeping our unit cool. I can understand why the 39' & 40' rigs might have a problem. I can also understand if you just wanted redundancy, but a properly functioning, stock basement air should be able to freeze you in a 32' unit.

mrschwarz · 06-24-2011, 10:26 AM

Actually, it's a 38' Meridian and the lack of cooling is well documented by others and me. I had a 34' Suncruiser with the same AC unit and it worked great. In basement air conditioning systems, there are two compressors and the air handler. One of the compressors and the air handler are on one power leg and the other compressor is on the other leg.

If the leg that only has the compressor on it is intermittent, how would you know? You may be able to feel the air movement from the driver's seat, but I doubt you can hear the compressors starting or stopping. I know that I can't.

This was the case with me. The leg with the air handler is fine so I was not aware that the second compressor was kicking in and out because of the transfer switch. I also knew that when driving, the AC wasn't as effective as when I was parked, but I assumed it was the heat of the engine that was causing it.

If it wasn't for the roof air and the sound of the blower starting and stopping, I still wouldn't be aware of the problem. By changing the transfer switch from generator priority to shore power priority, the problem was eliminated entirely. Whatever power source has priority requires the relay coils to be energized to work. Since the problem is eliminated by the change, it's clear that the mechanics of holding the contacts closed is good enough to handle driving. The energized coils while parked don't cause a problem either. The problem could be anything in the power path of the relay coils.

Like I said in my original post, you may be experiencing the problem and not be aware of it, depending if it was a partial failure or not.

tomsm · 06-24-2011, 12:22 PM

Michael,

Yep, you can pretty much scrub everything I said. I think the basement air works fine in my 36, but in anything larger apparently it's undersized.

I misunderstood on the transfer switch. I thought the whole switch was dropping out, not just 1 leg. If the whole switch flipped then, of course, you would lose everything and the load on the generator would go to zero - which was what I was picturing.

So, as Gilda Radner used to say "never mind"!

Have you been able to come up with any downside to changing priority on the transfer switch? I might just make that change for insurance. Certainly can't be good for those contacts to be opening and closing under load...

mrschwarz · 06-24-2011, 01:07 PM

Quote:

Originally Posted by tomsm

Michael,

Yep, you can pretty much scrub everything I said. I think the basement air works fine in my 36, but in anything larger apparently it's undersized.

I misunderstood on the transfer switch. I thought the whole switch was dropping out, not just 1 leg. If the whole switch flipped then, of course, you would lose everything and the load on the generator would go to zero - which was what I was picturing.

So, as Gilda Radner used to say "never mind"!

Have you been able to come up with any downside to changing priority on the transfer switch? I might just make that change for insurance. Certainly can't be good for those contacts to be opening and closing under load...

I believe it was Emily Latella that said that!

There are a few of disadvantages to having shore power priority:
1. Most transfer switches, mine included have a timer circuit on the generator side. This is to allow the generator to come up to speed and stabilizer before putting a load on it. When you swap the leads, you lose that.

2. As soon as you plug in shore power, it will switch over, even if the generator is running.

3. If you have the auto start feature for your generator, like I do, it will have strange behavior. If you are on shore power and lose it for whatever reason, the generator will start and run. As soon as power is restored, it will switch back to shore power and the generator will continue to run with no load until the demand is satisfied.

#1 and 2 are no big deal to me, I don't switch with loads anyway. #3 could be a problem, but only a minor one. Until I resolve this by either repairing or replacing the switch, I am going to leave it this way.

If you have a Parallax switch, this would be a good way to insure no problems.

I had a conversation with Troy at Winnebago. According to him, Parallax said that the primary use for the switch is dry camping, not running down the road. I will be setting up a poll to see if this is true for the forum members.

jdefant · 06-24-2011, 01:10 PM

I believe the Parallax Automatic Transfer Switch (ATS) works by energizing 2 power contacts (relays). When the switch is in one position, the relays are energized, and when the switch is in the other position, the relays are relaxed. There are ATS' out there that use solenoids to "pull" the switch to one position or the other. The solenoids are only energized long enough to throw the switch (sorry - off subject).

That being said, do you know if the relays in your switch are energized or relaxed when on generator power? My guess is that they are relaxed because I cannot believe a bump in the road would cause the contacts in an energized relay to open!

If they are relaxed when on the generator, then maybe the springs that hold the contacts together when in the relaxed position are weak or the contacts are slightly burned? I could understand in this case that a bump in the road would cause this problem. I doubt they are accessible but the point to my long reply is that maybe your ATS is bad and replacing it might fix the problem.

mrschwarz · 06-24-2011, 03:52 PM

Generator priority means that when the generator is running, the relay coils are energized. This is when the switch was failing. When I reversed the leads, it became shore power priority.

This means that when on shore power, the relays are energized. When on generator, the relays were not energized. The problem is when the relays are energized. When I was driving with the leads reversed, the problem disappeared.

I know the problem is with the transfer switch. I don't know if I can fix it or not.

I have never seen a solenoid-based transfer switch. I have only seen relay based.

RJay · 06-24-2011, 05:16 PM

Here is how I believe this problem occurs. If the A/C's are running when you get to the rv park and you connect your shore power before turning off the A/C's the transfer switch will transfer about 30-35 amps of load from the generator to the power cable. At that current level there is likely to be an arc at the contacts. Because of the weak tension holding the contacts closed it is also possible there will be a bounce of the contacts due to the forces generated by the current. Each time the contacts are closed under high current pitting occurs on the contact. Pitting is the formation of carbon on the contacts. Since carbon is an insulator the contacts start to heat up because of the high contact resistance. After a few cycles you have a downhill side to failure.

I have an Iota transfer switch but I turn off the shore power and reduce load if I'm going to exercise the generator; and when I switch it back I reduce load and turn off the generator before plugging into shore power. Unfortunately, I can't prove anything I mentioned above since I've never had transfer switch failure or seen one. But there is enough evidence that I'll take precautions.

RJay · 06-24-2011, 05:24 PM

Quote:

Originally Posted by mrschwarz

Generator priority means that when the generator is running, the relay coils are energized. This is when the switch was failing. When I reversed the leads, it became shore power priority.

This means that when on shore power, the relays are energized. When on generator, the relays were not energized. The problem is when the relays are energized. When I was driving with the leads reversed, the problem disappeared.

I know the problem is with the transfer switch. I don't know if I can fix it or not.

I have never seen a solenoid-based transfer switch. I have only seen relay based.

I may be wrong but generator priority means, under normal circumstances, the contacts are not energized when connected to the generator and energized when connected to shore power. This is so when shore power is disconnected the contacts revert back to the generator position ready to receive power from the generator and to eliminate any parasitic drain on the batteries.

mrschwarz · 06-24-2011, 10:46 PM

Quote:

Originally Posted by RJay

I may be wrong but generator priority means, under normal circumstances, the contacts are not energized when connected to the generator and energized when connected to shore power. This is so when shore power is disconnected the contacts revert back to the generator position ready to receive power from the generator and to eliminate any parasitic drain on the batteries.

That's not my understanding. The way I understand it is that if there is power applied from the generator AND shore power, the generator will get priority. When power is on both sides of the switch, the relay coils have to be energized. This means that generator priority means that the generator supplies power when the relay is energized.

mrschwarz · 06-24-2011, 10:55 PM

Quote:

Originally Posted by RJay

Here is how I believe this problem occurs. If the A/C's are running when you get to the rv park and you connect your shore power before turning off the A/C's the transfer switch will transfer about 30-35 amps of load from the generator to the power cable. At that current level there is likely to be an arc at the contacts. Because of the weak tension holding the contacts closed it is also possible there will be a bounce of the contacts due to the forces generated by the current. Each time the contacts are closed under high current pitting occurs on the contact. Pitting is the formation of carbon on the contacts. Since carbon is an insulator the contacts start to heat up because of the high contact resistance. After a few cycles you have a downhill side to failure.

In my experience building and maintaining factory equipment, a 50 amp relay is designed to switch on and off with a 50 amp load applied to it without pitting or other damage. It can probably handle more than 50 amps under a static load, but that's not really relevant. On the other hand, I suppose the transfer switch manufacturer could use undersized relays and call it 50 amps in the hopes that the users wouldn't switch it under load.

Be that as it may, that's not what happened here. I always shut off big loads before switching from one source to the other.

mrschwarz · 07-03-2011, 05:08 PM

I read in another thread that this is exactly what they do.

jdefant · 07-04-2011, 08:16 AM

Michael,

I think it is a really easy thing to test. Plug your RV into an external power source. It can even be 20 amps. If you hear a loud "thunk" (like I do on mine!) then the switch just energized and you have your answer.

mrschwarz · 07-04-2011, 09:38 PM

Already tested. The problem isn't that it doesn't work, the problem is that it doesn't hold when I hit a bump.

McDuff · 07-08-2011, 09:39 AM

Hmm, I wonder if I have an issue. We too always run gen and a/c going down the road and notice that the a/c does not nearly keep up as well as when sitting still. I assumed there was some outside air coming in somehow, even though we are buttoned up.

So, obviously the engine heater circuit is on leg2, for the problem to show there too. I am trying to think of a way to check this out before switching ATS wires(I'm in a wheelchair, tough to try to get to ATS), something like plug a clock, or even better, something that would not turn back on after a power failure, into the engine heater and check results after a road trip.