Intermittent Roof AC when driving

[mrschwarz]

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]

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]

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]

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.