A/C - OTR Heat blower motor kills engine

[Jim Eh.]

I went for a couple hour drive just to keep the fluids .... well, fluid and ran the OTR fan off and on for some circulation. But one time (smooth roads) I accidentally switched it to cool. Should not have been an issue as my A/C system is removed and the electrical to the condenser blower is disabled. However, I lost engine power and a bunch of dash lights came on. In traffic so I did not notice exactly which ones illuminated. When I switched it back to heat position (water valves all closed) it worked fine .... for awhile. About a half an hour later I switched the blower back on (heat position) and the same thing happened. Again weekend lake traffic prevented me from noting exactly which dash lights came on. I did not turn the blower back on even for a test as I had to park it (inside) and get home for dinner. I took a quick look around with lots of sniffs here and there but could not detect any smoke, latent or fresh so I thought I would be OK. Later this week I will disconnect the blower motor and energize the circuit to see if it is in the wiring as it seems strange for it to be the motor since it failed first in A/C position but was fine on heat position.

My question ... anyone ever experience this issue before.

[Iceni John]

Yes, sort of.   You have a DDEC engine, yes?   Several years ago my engine was mysteriously dying for no reason while driving, fortunately never causing a traffic holdup, but always very worrying to me.   At first I thought it was fuel-related, so I installed a fuel pressure gauge to see what the pressure was  -  no problem there.   At the time I didn't have a Prolink scanner, but the DDEC code readout on the CEL wasn't displaying anything amiss either:  a Prolink may not have shown anything anyway.   Then one day in the RV yard where I store the bus I was doing my usual pre-flight when it died again, this time after I turned on the high beams to check the headlights.   Aha!   A few minutes with my multimeter showed the problem  -  the main 100 amp Class H fuse on the rear start panel that feeds the front junction box was dropping voltage so much that the DDEC relay up front was disengaging, thus shutting down the ECM.   The cause was where the 4AWG cable was clamped to the fuse holder  -  it was so corroded and full of green crumbly stuff that I'm surprised any power passed through it at all.   I completely rebuilt the fuse holder, replaced all the high-current cables in that area, put fresh new lugs on every other fat cable, and changed every relay and all three solenoids  -  so far, no more sudden death syndrome.   I know the DDEC II ECM will shut down at about 10 volts, but in my case its cube relay was disengaging at a higher voltage than that, maybe about 10.5 or 11.

So, this is a wordy way of saying that when electrons cease to flow, you no go.   I suggest you also put in a really good voltage gauge so you know exactly what voltage is reaching the ECM;  I installed an AEM gauge that shows 0.1 volt differences, and now when I turn on the high beams I lose only 0.2 volts (the highs are 330 watts total!).

John

[richard5933]

There are lots of ancillary circuits connected with an OTR a/c setup. Some of these are designed to protect the a/c system, some the engine, and they usually kick in when some sensor sees errant data.

Any chance there was such a circuit (or part of one) left in your bus when the OTR a/c was removed?

[Jim Eh.]

Yes, sort of.   You have a DDEC engine, yes?   

So, this is a wordy way of saying that when electrons cease to flow, you no go.   I suggest you also put in a really good voltage gauge so you know exactly what voltage is reaching the ECM;  I installed an AEM gauge that shows 0.1 volt differences, and now when I turn on the high beams I lose only 0.2 volts (the highs are 330 watts total!).

John

Yes.
I will start at the breaker connections in bay 2. I was thinking the circuit going to ground and was looking for a "usual" suspect location.

[Jim Eh.]

There are lots of ancillary circuits connected with an OTR a/c setup. Some of these are designed to protect the a/c system, some the engine, and they usually kick in when some sensor sees errant data.

Any chance there was such a circuit (or part of one) left in your bus when the OTR a/c was removed?

It is definitely a possibility but I have probably 30+ hours on the bus since the system was removed.

[richard5933]

It is definitely a possibility but I have probably 30+ hours on the bus since the system was removed.

How many times in that 30+ hours did you accidentally turn on the a/c?

[luvrbus]

What are you using for batteries I have a cheap friend that kept his OTR and decided on 2 group 31 batteries was all he needed every time he turned the AC on the DDEC would shut down,start in battery compartment with the DDEC breakers wiring and grounds 

[Jim Eh.]

How many times in that 30+ hours did you accidentally turn on the a/c?

Probably once or twice

[Jim Eh.]

What are you using for batteries I have a cheap friend that kept his OTR and decided on 2 group 31 batteries was all he needed every time he turned the AC on the DDEC would shut down,start in battery compartment with the DDEC breakers wiring and grounds

2X  8Ds probably 3 years old with minimal cycles on them kept on a maintainer

[chessie4905]

Check voltage drop on voltmeter when engaging ac.

[oltrunt]

Stray magnetic fields near ECM circuits can cause engine shut down.  When my Ford Crown Vic was new I had repeated engine shut downs at highway speeds.  The computer showed a crank position sensor fault each time.  Ford replaced the cps three times and rang out the circuit and even replaced the computer to no avail.  I finally discovered that the problem only occurred when the a/c was on.  I put the car on stands, set the rpm's to about 2000, crawled under the car to watch as wifey turned on the a/c and sure enough after a few clutch cycles the engine died.  Looking at the wire loom to the cps I noticed about 2 inches of exposed insulated wire and just a hint of metallic shielding showing where the wires came out of the loom.  The cps loom is located about 1 inch from the a/c clutch.  I wrapped the unshielded portion of the cps wiring with aluminum foil being careful to overlap the bit of original shielding and the problem was cured.  That was 20 years ago and the problem has never resurfaced.

I wonder if somehow you are having a similar problem.  Jack

[dtcerrato]

Impressive find Jack!

[Jim Eh.]

Although I have run into shielding issues on ABS systems on older Volvo trucks, I don'r believe this to be any issue here as there is no circuit connected to the OTR A/C. To generate fielding issues there would have to be a complete circuit as in a magnetic clutch on an automotive A/C compressor or magnetic pick up as in ABS or a speed sensor that uses fielding to create a voltage drop.
I still have yet to have time to check the wiring at the breakers/contactor in the 2nd bay. It's that old time vs money thing. No time to spend and no money to buy it ... 

[Jim Eh.]

What are you using for batteries I have a cheap friend that kept his OTR and decided on 2 group 31 batteries was all he needed every time he turned the AC on the DDEC would shut down,start in battery compartment with the DDEC breakers wiring and grounds

Bingo Cliff. I had one cell in one of the batteries would short after a period of time. Took a while to figure that one out as they would pass a draw test when cold. Once the cell would short the voltage drop was significant enough to make the DDEC drop out. 

I also corrected the wiring to the vanner equalizer unit. The batteries were replaced when the unit was picked up in Reno at a truck stop. Real high quality batteries and incorrect wiring, I am lucky I did not do any damage to the equalizer.

New batteries installed, road tested and increased my standing time to 1 week+ so far w/o the maintainer plugged in.