High voltage, low OTR pressure, related?

[jelmore]

Had the OTR serviced about 3 months ago. Added 4 lbs 134A and some dye for leak detection later.

A week ago, the OTR didn't seems quite cold, but after about 10 minutes it seemed to work ok, though not really, really cold. Checked the refrigerant levels and the bottom sight glass seemed full and practically nothing in the top sight glass. The compressor oil looked a tad low, but it was showing in its sight glass, sloshing around.

Yesterday while under way the Hi/Low 24v voltage indicator on the dash was showing sporadically, never more than 3 seconds, and sometimes flickering. The analog voltage gauge shows pretty much topped out, just below 28v.

Turning on the 12v headlights seems to suck enough voltage to eliminate that hi/low warning light. Maybe the 24v regulator needs a slight adjustment. I think I can do that.

Today, though a nice day, I thought I'd run the OTR, and draw down some volts. Five minutes later, the OTR high pressure and OTR low pressure lights came on, the same indication as when I was low on refrigerant.

Turned off the OTR, a few minutes later the hi/low voltage light came on, turned on the headlights and no hi/low voltage warning.

Parked in high idle for 15 minutes, no headlights and no warning lights.

Haven't turned the OTR back on.

If you're still following this, are these events possibly related?

[Jon Wehrenberg]

Jim,

What was the actual voltage as shown on the gauge?

If the voltage indication light was really telling of a problem such as low voltage and it affected the condensing coil blower then the two can be related. A failed or slow running condenser motor would not pull enough air across the condenser and the AC system refrigerant pressure would increase causing the unit to shut down or at least give the warning.

[jelmore]

Jon, would high voltage have a similar effect? The actual voltage (as best I could tell) was 28v. Liberty manual says the hi/lo indicator turns on when the batteries are >30v or <24v.

I'm running now with the wabasto on (coldest temp) to run some 24v fans (I presume) and the voltage on the dial is 27.5v. I'm also running the headlights and the 12v side reads 13.3v/13.2v. No hi/lo warning for 50 mies. Jon--don't flip out it's Linda doing the typing!

[Jon Wehrenberg]

The reason I asked about actual voltage is because the Vanner monitor (in the rear above the chassis batteries) has failed on some coaches giving incorrect warnings.

It does not monitor the OTR so I am still trying to figure out how the AC warning light relates to all this.

If you get the Hi/Lo warning light again for chassis voltage check the voltmeter and see what it reads. At least that is easily checked.

[jelmore]

I'm thinking the OTR and voltage are not related. The OTR pressure warning isn't voltage dependent I don't think, so the only voltage effect would be on the condenser fans like you said. I'm seeing high voltage, so unless that blew a fan breaker I don't know about yet, then I guess I need to be looking at the actual voltages at the regulator and monitor; the OTR air can be dealt with later. I don't know about the equalizer. I've never seen exactly double the 12v voltage on the 24v gauge; the 24v side has always been a little higher. I don't know that I have the literature to test it.

I hope you're right on the monitor malfunctioning. I'm anxious to check that out. That would sure ease the angst.

Happy 4th, from Saint Ignace, Michigan.

[Jon Wehrenberg]

Jim,

You are mixing apples, oranges and peaches. Doing on-line analysis of problems is difficult because there are so many clues available when a person has some tools or meters and is standing next to the coach and on-line we have to ask and assume. Your last post suggests you are mixing up house and chassis electric readings.

Let me see if I can help you sort things out.

First, if you do not have a good multi-tester, you should get one. If for no other reason than to be able to obtain voltage readings not available from the coach gauges, and to check for power and open circuits. I will assume you have one, or for the moment you can borrow one.

Your 24 volt gauge is the chassis voltage. It only reflects the output of the alternator for the chassis (the big alternator). Your chassis electrical system alone is monitored by the Vanner electrical monitor. The only equalizer you should have is the 100 amp equalizer above the chassis batteries.

The voltage you should see at the 24 volt battery post, at the 24 volt equalizer post, and at the dash gauge is about 28 volts with the engine running on high idle, and with the engine off, and no loads you should see 25.5 (approximately). At the 12 volt equalizer post you should see one half the 24 volt value within 1/2 volt or 14 volts and 12.75 volts respectively.

If the actual voltage is around those values your chassis electrical system is OK. Those values will change downward as you put loads on the chassis electrical system, such as running the OTR or bus lights. With a healthy alternator and a voltage regulator working as they should the voltage drop will be minimal with the engine running.

Your comment about 12 volts suggests to me that you are interpreting the house voltage gauge as a reading of the chassis 12 volt systems. That is not correct. The house and chassis on your coach never merge. I believe you have a separate house alternator, likely driven from the fan pulley. That house system has no dash warning lights and is not a part of the issues you are discusssing. But just for your info, with the engine running the house voltage should be around 14 volts, and with the engine off and no house loads it should be around 12.75.

As to voltages affecting the OTR.....higher than acceptable voltages (30 volts for example) are not good, but it is unlikely they will shut down the OTR system or motors. Actually as voltage increases the motors draw less current so it is unlikely the OTR circuit breakers will trip. As the voltage drops however, the current draw increases and then the CBs will trip, but if they do trip you will have to reset them before the AC system will function. Your description of problems with the AC does not inidcate a tripped breaker. It may be coincidence the electrical HI/Low indicator is coming on when the AC warning is coming on.

[phorner]

Jon, my set-up is exactly as you described.

Jim, after reading your postings, is it at all possible that the HI/LO dash warning was the OTR AC pressure instead of the voltage?

If the indicator only came on for a second, especially while driving, could they have been mistaken?

[jelmore]

Jon, I have a 12v display and a 24v gauge that are both reading chassis voltages. The 12v display is part of what Liberty calls the Message Display Center. It's an LCD display is the lower left corner of the dash that also provides, among other things, engine oil and transmission retarder temps. The 24v gauge is a separate item. I have a multi-tester and will check the voltages when I can start up the bus without bothering the folks around me.

Paul, I'm sure I saw both types of warning. And I don't think they're related. They didn't happen at the exact same time, just during the same driving period.

I find it interesting that there was no voltage warning while stopped in fast idle; only while under way, and while under way it was sporadic. Almost makes me suspect a loose connection.

[phorner]

Jim,

FWIW, I had an intermittent indication on the dash warning lights of hi/low chassis voltage. Usually, it would come on when I first started up the bus and then be OK. Sometimes it would stay on for a few minutes and then go out.

I finally caught this display long enough to compare with the voltage gauge and, sure enough, the actual voltage was too low, then swing to correct.

As it turned out, this was an early indication of a failing voltage regulator. Took a while before it finally failed, as this occurred over several thousand miles and a few months.

[jelmore]

Paul, Prevost replaced the voltage regulator, along with the chassis batteries, a year ago. The voltage regulator is the new style, whatever that means. It looks like it has red loctite all over the adjustment screw, so before I mess with adjusting something, I need to check everything else out. Thanks for all the help.

When I take a voltage reading at the regulator, what is that voltage ... batteries? alternator? Are they the same? The field wire, is that what tells the alternator how much to put out?