Resolved Simple (maybe) HVAC question

[nowherejoe]

Actually 2 questions. We have just acquired a new to us 2004 Newmar Mountain Aire Class A (workhorse & 8.1). In going through the HVAC system (front and rear Penquin heat pumps) I have a couple of questions... first the easy one- Where is the Zone 1 remote t-stat located? The CCC is in the control cabinet above the door but I have to believe there is a remote sensor somewhere however I cant find it. The Zone 2 remote is mounted on the interior bedroom wall, passenger side but no sign of one for zone 1 anywhere.
2nd question, (maybe it's a failure)? Zone 2 will not operate in a 'fan only mode' mode. If I go to cool, system will go through it's normal 2 minute time out then compressor and circulation fan will start. I can change fan speed in this mode, low, high and auto all function as they should. If I change the mode to 'fan only' the entire unit will shut off. If I select 'fan only' and any fan speed nothing ever happens. On zone 1 I can select 'fan only' and the blower fan will run, never cycling the compressor. I can change between speeds and everything works as I would expect. So my question is-- is this the way it's designed or do I have a problem with the zone 2 unit? Thanks for any light someone may be able to shine on this for me.

 

[Neal]

Welcome @nowherejoe. There should be a small black "thermistor" they are called which are the sensors the T-STAT is using for the two zones. I don't know in your specific coach but mine is outside of the half bath on the interior wall and the other is in the bedroom. Newmar has been moving these around trying to find the best spot. Hope you can spot the black plastic device attached to a wall or cabinet.

I don't know the answer to the 2nd question. Maybe Dometic can help?

 

[nowherejoe]

Thanks Neal for the quick response. My sensors (at least in the bedroom) are white and as I said in the OP, I located the one in the bedroom for zone 2. I was hoping someone with a MA 3778 of similar vintage may be able to let me know where their sensor for the front (zone 1) is located.

 

[Just George]

@nowherejoe I have a different coach so no first hand knowledge here but If Zone 1 is the front & the thermostat is in the front perhaps the sensor for Zone 1 is part of the thermostat. If all else fails give Newmar a call they should be able to help.

 

[nowherejoe]

My sensor location has been solved. Seems Newmar hid the zone 1 temp sensor under the dry bar cabinet lip...it is on an inside wall. thanks for the feedback.

 

[Old-RV'er]

In A/C units (heat pumps as well) and the coach is 2004, I suspect the start capacitor in the a/c unit is marginal. They last about 10 years or so, changing one is hazardous, so unless you know what you are doing I would leave it to someone who knows. I know how, but will NOT outline it here. Not that I want you to spend money, I don't want you electrocuted. Capacitors store huge amounts of electric voltage/amps, contacting one inadvertently, can kill you. At the time of inspection by qualified technician, have him ensure no lose connections, as that is the other thing it could be especially as described, the compressor/fan does start when in A/C mode. And long shot, but thermostat could be faulty, there was a rash of them in the early 2000's. As Neal Suggested, call Dometic.

 

[nowherejoe]

Thanks Old-RV'er. I ordered a cap for the unit (no worries on procedure, I'm trained electrically- 40+ years in industrial maintenance), but I'm skeptical since the unit operates properly and reliably in cool mode. Since the t-stat/unit communication is serial data and zone one works fine I'm thinking the most likely culprit is the control board in the unit, maybe a bad on-board relay. Electrically the unit is a bit of a rats nest, someone's obviously been there before so before I start changing parts I will clean everything up, re-terminate all the connectors (which may help with any potentially bad connections) and temporarily swap the control board with zone 1 to see if the issue follows. If it does, I'll order a new board. If not I'll swap back and try the cap. Thanks again for the input, it seems you and I were thinking very much along the same lines. Once I have it going I'll update the post. May be a while, lots of other irons in the fire. Retirement sure is a busy job!

BTW- if anyone has any suggestions on how to get through to technical support at Dometic, I'm all ears. Their automated service wont let me get through to anyone without an account number...

 

[Old-RV'er]

Hmmm, I would try to call "an authorized Dometic service center" and ask them how to contact the main office. Do a google search on Dometic and see if you come up with a different number than what you are using, they may have back door, someone has put out to the world. Like trying to get help from Microsoft, impossible.

From another post on similar subject, severe shortage of A/C's system wide, and if needs new board, you might try "dinosaur electronics" In Oregon. Believe still in business, see link below.
Excellent boards, all double soldered.

Since yours is a 2004 unit, it's at or near end of life, so a new A/C unit may be in the offing down the road. No sense in putting a whole bunch of money into it, if it's close to another type of failure. That then leads to a whole other bunch of compatibility problems with the T-stat, etc. So, as an alternative, do a search on YouTube about "RV Salvage Yards" and see if there is one close to you with a MH model like yours or close to it, with a slightly used a/c unit which will match up to your system. Although, it may be easier with Newmar, with lots of older MH's, getting a new "electronic" ac to work with an older mostly analog system is a nightmare. Try those options, think success is just around corner. Good Luck.

Dinosaur Electronics Home. High quality circuit boards for RV appliances.