Replace two rooftop dometic ac's

[Joel Sheriff]

I'm still having issues with rear ac unit now front 15k unit is doing same kicking off breaker or GFCI under load. Spiking between 16 amp and 50 amp when compressor tried to kick in after startup.  Want to replace both and would appreciate suggestions on good tech or shop to do replacement.  I'm in SoCal but will travel if worth the trip.  I'm done fixing want to replace.  Should I invest in good electrician first to see if it's electrical?  I replaced the breaker for the front, and gfci didn't work with new breaker either.  But I'm concerned that both ac''s are reacting at the same time. Could it be coach electrical before replacing $5k in ac' s? 

[Tom Cherry]

Some Questions

1. where are you reading the current or amperage spikes?  Your EMS should not be displaying current readings when you are on 50 or 30 Amps????
2. how old is your GFCI? I THOUGHT you had reported it was replaced ...maybe within last two Years or so. Are you referring to the GFCI receptacle?
3. There should be TWO 20 A REGULAR circuit breakers.  Do you have GFCI CB on your HVAC units.  if so, those should be only REGULAR, non GFCI.  

Just a little confused....can you provide details? 

[Joel Sheriff]

When I tried the Gen 50amp power not shore I was getting reading on the EMS board. It would start up at 17 or up to 20 amps then spike to 40,50 or higher when compressor tried to kick in and when spiking high enough it blows the breaker from front air and the GFCI when rear air starts. Rear air does the same spiking of power it starts at 16 or 17 amps then spikes higher? Gfi you're correct was replaced with the compatible gfi for my system. One that tech replaced didn't work with my unit so you mentioned a while ago the compatible names of some companies. My ac is a single 20 amp breaker each not GFCI and I changed out front breaker and it still occurred. 

Yes the gfci receptacle

[96 EVO]

Have you replaced the start capacitor?

I lost the capacitor on one of my units, and seen some crazy high amp spikes when the compressor tried to start!

Edited April 11, 2023 by 96 EVO

[Tom Cherry]

2 hours ago, Joel Sheriff said:

When I tried the Gen 50amp power not shore I was getting reading on the EMS board. It would start up at 17 or up to 20 amps then spike to 40,50 or higher when compressor tried to kick in and when spiking high enough it blows the breaker from front air and the GFCI when rear air starts. Rear air does the same spiking of power it starts at 16 or 17 amps then spikes higher? Gfi you're correct was replaced with the compatible gfi for my system. One that tech replaced didn't work with my unit so you mentioned a while ago the compatible names of some companies. My ac is a single 20 amp breaker each not GFCI and I changed out front breaker and it still occurred. 

Yes the gfci receptacle

OK...for me as well as others....

Your Front and Rear HVAC (AC) circuit breakers are plain ones....NOT a GFCI style...

Next, I reread your previous post as well as the PM's we exchanged.  From WHAT I gather, you had a Tech install a capacitor on the front unit as it was acting up.  I do NOT know if he installed an OEM or simple one or whether he upgraded you to the soft start which has been advertised to "keep the current low" as the compressor motor is older and requires a higher starting current.  Do you have an UPGRADED SOFT START or just a Replacement Capacitor.....this is on the FRONT.

I also understand that you have issues with the rear AC.  As I advised in our PM, it may be more cost effective to replace BOTH the AC (HVAC HP...I THINK) units and also upgrade (you MUST) to the newer, smarter Dometic Thermostat....than to keep working on the older ones.  You being a full timer have at least 10 times the hours on your units than most of us do....and many are experiencing issues with units the age of your system.

NEXT UP.  Your EMS will NOT, when on 50 AMP display any current.  The System ASSUMES, since it reads 240 VAC across Line 1 and Line 2, that you have 50 Amps. However, you have a 7.5KW or an 8 KW 120 VAC Onan generator.  It had TWO Lines....Line 1 and Line 2.  These are 120 VAC and NOT OUT OF PHASE.  Therefore, the EMS does not sense or read 240 VAC as the lines are in phase...or the same.

What you are reading on your EMS is the total current being drawn or used by BOTH these lines.  The "Spike" (50 Amp?) you see is tripping the Individual (or should be) main 120 VAC 20 Amp circuit breaker.  That indicates that the motor is overloaded.....during startup....and might be "worn" enough to draw way too much current. 

Now, if you recall when you had the issue of the failure of your EMS circa 2015 or so....what the EMS is reading is the TOTAL current from both lines.  Ordinarily, when one of your units comes on or the compressor starts up, you MIGHT see 17 or 18 amps.  Then it will drop back to the 13 - 15 Amps and run there....there is ALWAYS a start spike in the compressor.....but your HVAC units seem to be drawing TOO much current.  The Soft Start Capacitor kit has some "Electronics" to dampen that and will let a worn or older unit not require the high spike.  I hope that makes sense as that is how I understand it.  These kits are upwards (or were) of $400...and require some wiring modifications.  Adding two of them could be maybe $1,000 so that is why I suggested, in my PM, that you do some research on two new units and do a complete replacement rather than pouring more money into an old system....that will eventually, probably sooner than you want, fail.

As to the GFCI. I THINK that the high starting current is triggering a "False" signal to the GFCI.  It is very hard to diagnose or determine if that is the issue.  If you do NOT run the AC's and you can run your microwave or such....remembering that you DO have limited power from the Generator.  Also please do NOT overload your generator....like before.  If you exceed 50 amps (which is the combined load of line 1 and line 2), you risk damaging your wiring as your cables, like all Monaco, are only rated, when on Generator for 50 Amps.....not 60.

Hope this helps....

 

[Martinvz]

I agree with Tom re upgrading the thermostat if you were to replace the a/c, as that is about $120. Call Dometic as they provided a lot of help when I needed it. To keep the old thermostat will cost about $200 per a/c for the replacement control board to work with the old 5 button thermostat PLUS about 2 hours of labor to install the replacement board. Better to buy the new 10 button thermostat.

I just replaced one a/c and that is my experience as my other old a/c is still working . My old 2006 a/c had an external box with the control board separate from the a/c, sitting in the airflow. The new Dometic Penguin II has an onboard control board. The wiring is a breeze. The 120V connection they now use is a bear, jmho.

There is one connector in the old box that I could re-use for the new a/c with the old thermostat rather than rebuilding it using the pigtail Dometic provided.

[Joel Sheriff]

Tom, as usual you make total sense and have the issue spot on. I Did not use a soft start on the rear unit but I did add an hd capacitor in line with the standard capacitor. Did not try the added capacitor kit on the front unit yet. Since the rear is for all intent fried I may take that capacitor off and try on the front which just started the spiking of power. The both capacitors were recently changed so they are good as I know it. I'll have them checked again. The front had a motor and capacitor changed within the last year. Don't really want to invest in the softstart but have made and awaiting answers on replacement of both to the upgraded dometic low profile heat pumps with the electronic 10 button thermostat. The gfi when not using air units, is fine with all other appliances even upwards of 40 amps usage no issues with gfi.  Looks like it's total replacement at this juncture.  I'll keep the lines open with revolution. 

[jacwjames]

FWIW,

I started having intermittent tripping of the breaker on the front AC in 2015, ultimately found the motor was almost seized so I replaced.  I started seeing high amperage on startup when plugged into 30 amp.  When I checked the motor I could barely rotate it with my hands.  Found a replacement motor for ~$125 so it was a not brainer to try and fix.  I worked great for the next 5 years. 

In 2021 my wife had a problem with the rear AC, it was making noise so I suspected the rubber isolation bushings were wore out so I tore into it.  The bushings were wore out ant the motor was tight so I looked for a replacement>>> none to be found.  So I decided to bite the bullet and replace both AC's. 

I did this myself, not too hard, found 2 AC's at PPL for a good price.  I have easy access to the roof from on top of the workshop I built in my garage, I was able to use a moving dolly to move the old AC's off and new ones on.  Wiring was not hard, I labeled everything and took lots of pictures.    I opted to go with the MicroAir instead of the 10 button CCC, it was plug and play, the MicroAir is Bluetooth and WIFI capable, a really nice feature. 

One thing I did while I was waiting for the new AC's was to take a good look at the AC duct work using a remote camera.  I found come mouse holes that I was able to repair but the biggest  issue was there was a duct joint that was not sealed properly >>1/2" gap on 3 sides where the air was just dumping to the ceiling.  I could tell the difference when I started using the new AC's!!

 

[klcdenver]

Jim,

I also have a 2007 Diplomat. 2 years ago I replaced my rear Dometic Penguin. I have the silencer on it also. I recently replaced the front unit with the Houghton which is about half the price of a Dometic. I just finished a 2 week trip using heat pump and A/C. The Houghton is a lot quieter than the Dometic. If you went with the Houghton you can also keep your current thermostat to control your 2 furnaces. Just food for thought. 

[Joel Sheriff]

Ken, is the Haughton similar in features, installation etc. Anyone else have experience with Haughton. 

[klcdenver]

The installation of the Houghton is about the same as the Dometic. No modifications required. You just keep the control board from the Dometic so you can control the furnace. The Houghton has a remote control to control it. Here is a link describing my installation.

 

[Tom Cherry]

1 hour ago, klcdenver said:

The installation of the Houghton is about the same as the Dometic. No modifications required. You just keep the control board from the Dometic so you can control the furnace. The Houghton has a remote control to control it. Here is a link describing my installation.

 

Ken has one, at least to my knowledge, of the few successful conversions.  This topic should be a text book for any Houghton conversion.  We talked a few times to verify and he provided Frank McElroy and myself with a lot of good information so we can assist others.  However, there are at least 2 other topics that have not or did not have such a happy ending.  The decision to go to the Houghton, for the average owner, that will depend on a "Tech" that is a yank and replace should be carefully considered.  Ken fully understood and maybe learned a little along the way as to HOW it has to be done.  

Some members have yanked out and thrown away the control modules.  Then tried to backtrack and can not isolate or find or "rewire" their old 5 button thermostats to make the furnace controls operate properly.  There are older examples where there was a simple (not 5 button) thermostat that could not be installed.

My advice to Joel or others.  READ KEN's TOPIC.  It is TEXTBOOK.  

If you understand that the downside to this, rather than the Penguins...and I have NO IDEA ON COST...is that salvaging the 5 button thermostat is a good idea if your thermostat is in good shape.  We have have posts where the out of production 5 button thermostats have or are getting more scarce and the supply of rebuilt ones is drying up.  In Joel's case, I would add that his thermostat, in my thinking, is NOT a candidate to be kept.  He has full timed for at least 10 years or so....or maybe longer.  I personally would not try to salvage the Dometic components and this thermostat.  That MUST be done as that is the only practical or simple way to control the furnaces.  The tablet or phone apps for the Houghton will not control a furnace.

The other drawback is finding a tech that COULD understand and follow Ken's topic and then salvage both units.  That will add a few hours or maybe a bit more....as he will have to "Educate" himself....then pull the control units and then Joel will provide him with the box (I think that Joel has a 15KW unit) to mount the control box inside.  The 15KW modules are in the roof top and have to be pulled and the wiring marked to then put the module in the enclosure and then mount in the Houghton plenum and be properly wired.  The 13.5KW are inside, but must be left in place and NOT pulled out...

I believe that many of our members here have more skill set information and understand the multiplexed Dometics than do a lot of "field techs".  We had one member that has lost an AquaHot zone after a reputable and highly recommended shop replaced all three of his Dometics in a Dynasty. The tech was just a "Tear out and put in" tech and did not have a clue that there was a FOURTH zone (Dometic Control Box) that SHOULD have been replaced.  He is having difficulty in explaining to them what is on the print.  They seem to refuse to believe he knows what he is talking about and he will have to order the part or sit down with them with the print and convince them the ONLY WAY to rectify the problem is to remove the OLD "AC Brain" that controls that one AH zone and install the CORRECT or new one.  He is very frustrated, especially after spending $8,000 and now has the frustrations of getting an incomplete job completed.

That's my take.....and it has a bit of personal input as Joel and I have been working on things that broke, on the phone back to 2014....

BUT...again....Ken's work was excellent and we all learned.....and it will be invaluable to others that do go this route...

[Joel Sheriff]

Well received Tom, back to dometic. Thanks 🤔

[96 EVO]

6 hours ago, klcdenver said:

The installation of the Houghton is about the same as the Dometic. No modifications required. You just keep the control board from the Dometic so you can control the furnace. The Houghton has a remote control to control it. Here is a link describing my installation.

 

Do the Houghton heat pumps use remote temp sensors?

[Tom Cherry]

On 4/12/2023 at 2:05 PM, 96 EVO said:

Do the Houghton heat pumps use remote temp sensors?

I don’t think so.  There was a topic where the availability of tech support (Magnum) was discussed.  That allowed me to discuss (vent) some hostilities and frustrations with tech support when I try to help a member.  Here is the text from that.  It addresses and also provides a little more insight into the issue with the RecPro Houghton….

While doing some research for an alternative method or easy non “intrusive” way to assist folks that are having difficulties with the Houghton units and no way to control furnace (AquaHot), I stayed on hold for 30 minutes with RecPro their supplier and tech support….and then finally, Operator NOT Available….leave a Voice Mail.  

Then tried MicroAire (the BT and Wireless Thermostat Alternative).  I had talked to them before and their systems will ONLY replace a completely and fully installed HVAC system….and support 4 Brands.  This time out, they have dropped all phone support.  I checked their documentation and website and they do NOT offer a replacement that has a controller or such to modify and use on a RecPro Houghton nor for a stand alone Furnace….

However Coleman/RVPro/Axcel(sp) did have a short wait time….and the tech answered my questions about their universal hard wired Thermostats, but had no knowledge of the Dometic system and the phone MPX systems….so STRIKE 3….but they were nice and knew their products….

I had already called Ken (from Denver) and we discussed his successful Hourghton install…where he researched and experimented with the Dometic  5 button and kept the needed control modules….and it works.

He and I concluded that if he ever lost the 5 button, he would abandon and wire in a new thermostat from each furnace. There is some info in various posts, but the only easy and feasible alternative is the “Line Voltage” as it requires no power (12 VDC)….just 2 wires…. You can use a conventional RV 12 VDC thermostat as long as you can run 12 VDC, but you will need 3 wires….power in & Ground & Signal out.  The signal out (typically Furnace White) is a 12 VDC signal and you will need a Bosch relay and Ground inside the Plenum.  The two “blue wires” going from the original Dometic Controller are then attached to NO contacts of the relay.  When the thermostat calls for heat, a 12 VDC signal will be sent….energizing the relay.  The Atwood furnace and the AquaHot control board require a “dry pair” of contacts like a light switch….turn it on for heat…off to stop.

That would require a line out over the ceiling and down the wall to a thermostat….for each system….wires would in a wire mold piece of flat “conduit”. OR from the Atwood board.

I was looking for a wireless (battery powered) thermostat with a 12 VDC slave controller with with either a 12 VDC signal out to a Bosch relay or a dry set of contacts.  Could not find one.  Alexa has the potential but did not get into the interface as most are 120 VAC.  That MIGHT work….as there is “hot” 120 VAC in the Plenum….but the various furnace interface devices and Alexa’s ability to read a wireless thermostat and then route the control signal to a furnace controller that is really simpler than most would be a bit of a project that I chose not to design….others here have the expertise….and might chime in.

BOTTOM LINE.  No tech support from either Hiughton or MicroAire (SP).  So the reservations about the Houghton still exist.  I did find several Airstream blogs and this was the number one issue and many had used the “most trusted and experienced” vendor/installer (they did everything but pray to him) and no one, not even him, had a solution….other than a standalone remote thermostat.  That sort of nails it…..