APU shutting down question?

jamom123 · Jan 30, 2014

Last night here in GA it got really cold it's actually 1 degree right now. My question is i have a carrier APU and it works great. Well when im at home and not sleeping in the truck i leave the temp start on so it will crank and warm up the truck. It always works really good but early this morning while i was on the phone with dispatch i heard it crank up and start running and it is set to run for one hour. Well after about 20 minutes i heard it shut off. I went outside and looked at the display and everything seemed fine. So i manually cranked it and turned on the heat it did the same thing after about 20 minutes it shut off again. Does anyone know what the reasons could be that it is doing this? Like i said it's about 1 degree here right now, im going to check it again after it warms up some. Thanks.

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davekc · Jan 30, 2014

Could be a couple of things. When was the last time you changed the fuel filters? Remember, those Carriers have two fuel filters rather than one.

jamom123 · Jan 30, 2014

Well I went back out after I had the truck running about an hour and I cranked the APU back up now it has been running fine with the truck engine running too. Do you think it could have been the fact that it was just cold and it hadn't been running? As for the fuel filters I had it changed about 550 hours ago. I didn't know there were two though.

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davekc · Jan 30, 2014

Since it shares the same coolant system, it probably helped when it warmed up from the truck engine. There is a primary fuel filter on the engine and the secondary one is a in-line filter.
It is small and on the fuel line. Many times people forget to change that.
If it does it again, I would probably consider a change on both if you are at 550 hrs and unsure whether it was changed previously.
Also when changing the in-line, make sure you install it the right way.
Arrows on the filter tells you the way to go.

jamom123 · Jan 30, 2014

Thanks for all the help dave.

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davekc · Jan 30, 2014

No problem. Hope it helps.

jamom123 · Jan 31, 2014

Update on the APU troubles last night I fired up the APU right after I turned the truck off and it came on and was running fine then after about 1 hour it shut itself off and said under voltage. I cranked it back up and it done the same thing, then I cranked it and just let it run without running the heat and it ran fine. After a couple of hours I woke up cold turned the heat on and it did the same thing after about 20 minutes. I did this a few times throughout the night. It will run fine until I turn on the heat then it shuts off and says under voltage, I finally had to run the truck. Does anyone know why it would be saying under voltage? And how I can fix this. Thanks.

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jamom123 · Jan 31, 2014

I called and talked to Carrier they told me it sounds like the generator may be going out.

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Dynamite 1 · Jan 31, 2014

since carrier is the same as pro heat they have electric heat in them. since you are getting a low voltage only when running the heat. i would say there is a problem with the thermo fuses in the heater. sounds like they are going bad and drawing to much current. if it quits blowing heat all together you will know for sure. there are two of them. one for low heat and one for high heat.

take this information in presumption that the units have not been changed all that much since carrier got involved but i dont believe they have.

Dynamite 1 · Jan 31, 2014

jamom123 said:
I called and talked to Carrier they told me it sounds like the generator may be going out.

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did not think of that. good possibility there.

davekc · Jan 31, 2014

Very possible on the generator. Could also be a bad ground or a bad board as well. One of those just going to Carrier and let them run some tests on it.