Carrier Comfort Pro APU cranks, doesn't start

bugman · Apr 2, 2011

After adding oil, my APU cranks but wont start. I drained the fuel filter,fuel was clean, hardly a trace of moisture.

Truck is 06, not sure of year of APU, was in truck when I bought it. 6500 hours on APU and I was about to have PM done on it and truck which I will do anyway. It ran fine night before. I don't check oil on it near often enough. Was fueling, checked oil and noticed none on dipstick. I added about 2 quarts which was an over kill.

Any ideas? I am hoping there was some sort of re-set that got tripped when oil got low even though I think it was running fine when I started up main engine that morning.

Thanks
Ron Johnson

davekc · Apr 2, 2011

Probably sounds stupid, but where did the oil go that was in it?
Might want to identify that problem before doing anything else.

bugman · Apr 2, 2011

Thanks for the reply. I never leaks a drop. I suspect this is just regular use for an engine with 6500 miles.

davekc · Apr 2, 2011

Hard to tell but worth checking. If no codes are on the display, then it could be sensor, fuel switch, fuel pump, or wires/fuses at the panel. After that, I would take it to a carrier dealer if you aren't familiar with working on them and covered the items on the troubleshooting in the manual.
Good luck.

bugman · Apr 2, 2011

Yes, that is my thought. I am just hoping there is a reset that needs to be tripped and that someone has had this same problem. I was a certified mechanic till my son was born in 78. I know my way around an engine, I just know nothing about this APU and don't have a manual. But I will be ordering one

jansiemoo · Apr 3, 2011

Seperate from your oil problem, we had the same cranking-no start. Had BOTH fuel filters replaced, worked for 20mins, died, primed again, died again...long story...take up tubes were too short/placed wrong. Also the thing needed alot of priming.

Dynamite 1 · Apr 3, 2011

on a rigmaster, if you over fill a bunch or fill to fast the oil can over run and get in the cylinders and it will crank but not run. hope thats not the case. not a killer but a pain from what i have been told.

LDB · Apr 3, 2011

Yes, Rigmaster is bad about having to be filled slowly or it won't start. Eventually it all settles in and will run again but not until then. BTDT at Speedco once. Good luck.

davekc · Apr 3, 2011

Just a FYI. I think you can go to Carrier's site and download the manual for free.

highway star · Apr 3, 2011

Dynamite 1 said:
on a rigmaster, if you over fill a bunch or fill to fast the oil can over run and get in the cylinders and it will crank but not run. hope thats not the case. not a killer but a pain from what i have been told.

Actually, it won't crank. The oil is too thick and won't compress enough to complete the stroke. Well, that's what happened to mine, even after telling the professional oil change technician to fill it slowly.

layoutshooter · Apr 3, 2011

My Pro Heat has hours on it similar to yours. It too uses oil. I have to keep a close eye on it. It is always a good idea to check it often anyway. I have yet to have your problem. I have had a dipstick break once.

bugman · Apr 4, 2011

jansiemoo said:
Seperate from your oil problem, we had the same cranking-no start. Had BOTH fuel filters replaced, worked for 20mins, died, primed again, died again...long story...take up tubes were too short/placed wrong. Also the thing needed alot of priming.

Thanks for the reply. So you are saying the pickup tubes in the fuel tank were too short? But I still had plenty of fuel to run truck engine. Also, you mentioned priming. Is there a manual prime pump on this APU?

highway star · Apr 4, 2011

bugman said:
Thanks for the reply. So you are saying the pickup tubes in the fuel tank were too short? But I still had plenty of fuel to run truck engine. Also, you mentioned priming. Is there a manual prime pump on this APU?

Your APU has its own pick up tubes. It's common in RVs to have the tubes short enough to not run the RV out of fuel, usually leaving about a 1/4 tank. I don't know if this would be the case with your truck.

purgoose10 · Apr 4, 2011

Since it's that old and you don't check it much I would also check the water lines to see if they are collapsed. If they run hot the sensor will shut it down and won't let it crank again. When they install those things they take the shortest route with hoses and wiring. If they are laying on the frame rail or tied up they could be collapsed.

bugman · Apr 4, 2011

Thanks purgoose, That sounds logical. I am in line now for the PM on truck and APU. My only thought against what you are saying is that the APU is staying just as hot as if it were running, so there is enough coolant circulating for it to absorb lots of engine heat from main engine

LDB · Apr 4, 2011

My Onan is set up to only run with over 1/4 tank of gas in the van so that in theory I can drive somewhere to fill up rather than wait on road service. I wouldn't want it to draw down any farther.

purgoose10 · Apr 4, 2011

bugman said:
Thanks purgoose, That sounds logical. I am in line now for the PM on truck and APU. My only thought against what you are saying is that the APU is staying just as hot as if it were running, so there is enough coolant circulating for it to absorb lots of engine heat from main engine

Remember they have a thermostat also so if it's hot the celluloid might have shut it down. Have you checked to see if it's got fuel pressure?? If your not pumping fuel, well self explanatory. Just have to go thru one at a time and check it out.

One other thing. Make sure the fan for the unit is working. Old unit might have a short.

jansiemoo · Apr 6, 2011

bugman said:
Thanks for the reply. So you are saying the pickup tubes in the fuel tank were too short? But I still had plenty of fuel to run truck engine. Also, you mentioned priming. Is there a manual prime pump on this APU?

Oh, now you're asking technical Qs? Lol

um, there was an accordian looking thingie that you squished together to prime. The second techs that looked at it were sure it was air in the system...I just asked the hubby, he says it was a combo of air in the system and a bad fuel pump. But the air was partly due to running it when the fuel was below the level of the pick up tubes.

geo · Apr 10, 2011

give bill more a call at tsi he's works wonders on gen set
he's off of i76 north jackson oh ex 57 i think
he also western star dealer to

BillChaffey · Apr 11, 2011

Since this was eight days ago it may be fixed. One if not the first thing, you need to watch the exhaust and see if anything is coming out. It can crank forever with no fuel going into the cylinders.