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Houghton A3800 - a great heat pump but what you should know before installing them


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Yesterday we had both of our old Dometic Duo-therms, that had died, replaced with new Houghton A3800 heat pumps from Recpro. One small thing turned what should have been a relatively quick process in to a long drawn out affair. The Houghton units arrive complete with everything you need for most installs. The catch is the 4 hex head bolts that draw the roof unit to the ceiling bracket that forms a tight seal. Houghton provides the 4 bolts that are suitable for most installation on roofs up to 5-1/2 " thick that are flat. If you have a slightly curved roof like the one on out 2005 Safari Cheetah there is included a 1-1/4" thick foam rubber gasket to isolate the A/A from the roof and provide proper seating. Unfortunately, the gasket combined with the thickness of our roof resulted in the the bolts being about 1-1/4" short. The Duotherm bolts on the old units were long enough but were 1/4"-20 coarse thread. The new bolts supplied by Houghton are M8-1.25 metric fine thread. Our solution ended up being to use M8-1.25 threaded rods plus M8-1.25 couplings in conjunction with the supplied bolts. Because of the length of the supplied bolts they had to be cut, as well as the threaded rods. I ended up having to drive to 3 different stors in three different towns to find all the parts needed to complete the install. If you are planning to install Haughton a/cs on a thick roof coach I recommend getting the proper length bolts in advance of starting the install so that it will go much easier and quicker. Without the bolt issue this would have been a very quick and easy install. The new A/Cs are great!  

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Quite a sales pitch on the RecPro website "This isn't just a cheap rooftop AC unit. Unlike other models that are made of cheap plastic that has been molded to shape around the unit, these are made from high-quality, tough plastic built to withstand what life throws at it. In warmer climates, other models of air conditioning units can melt from the heat." and they show a photo of a melted Dometic.  Funny!

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These look like nice units!

Per the internet........If the roof's thickness is greater than 3 3/8", you can purchase a thick roof kit
Minimum roof thickness is 1".....

But I wonder if the "nuts" could be changed or "tapped" with a 1/4-20 tap so you could use the original bolts?

Were you able to use the 'factory thermostat' that interfaces with the gas furnaces?

 

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Hello everyone,

I just installed the RecPro 3800 (ducted) into my 2000 Dynasty into the rear A/c unit.

A few additional points and things that caused us issues. The RecPro will not interface with the old thermostat. That was why we just did our rear unit. Our rig had a thermostat for the back A/c and a thermostat for the heater & a/c for the front unit - they are not connected in my rig.  So by just doing the rear unit I don’t have to deal with the furnace (yet - sometime I will).

The bolt holes are in different places. We have a 1/4” metal bracket (layer) built into our roof. So we needed to drill that for the new holes. Unfortunately, my new holes didn’t line up as well as I wanted them. I ended up cutting the corners off the black plastic plenum mounting bracket (and just screwing that to my ceiling) with the A/c bolts on each of the four corners.  It works fine and is very solid. 
 

Ducted.  In my Rig, I have ductwork in the roof for the vents. The ducted RecPro directs the air flow out the front and rear of the grill. I solved this by making a rectangular ducting to direct the air flow into my rigs ducts. I did this by cutting up some 1” insulation into the proper size then using 3M silver heat tape, stacking 3 of them plus some weather stripping to direct the air into the ductwork. Hopefully not too much air bypassing the duct and re-entering the A/c (although I am sure some does - because I couldn’t get a complete seal between the two different surfaces).

So far in testing it is working very well. (I just completed the project a couple of days ago). It did take me much longer than I thought- but I am a slow builder when I am problem solving as I go. 

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5 hours ago, Mike Farquharson said:

Thanks for the info , was your systen a ducted and if so how did you connect to the duct and how long were your bolts.

 

Thanks Mike Farquharson

Thanks MIke. Our rig is ducted with the ducts running the length of the coach (passenger and driver side) from living area to bedroom. With this configuration the ducts are served by either the back a/c or the front or both. The Houghton 3800 plenum grill has a front and rear facing adjustable fined air dump for quick cooling. The rear facing vents have a slide damper that can be closed partially or fully directing more or less air into the ducts. The front facing "dump is not controlled by the slide dampers but the fins can be closed. Even with them closed there is some air leakage when the unit is operating but the  fan moves enough air that most comes out the ducts. Yhe air volum is considerably more than with our previous Duo-therms. With the duo-therm fan on high and the dump baffle closed you could barely feel air coming from the ducted vents. With the Houghton 3800 and the from set on medium you can feel air blowing from the ducts when 6 feet away. 

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Clubflyer, the thick roof adapter kit is designed for non-ducted roofs so conditioned air moves from the roof unit to the ceiling defuser without loss into the roofing material such as insulation. In a ducted roof there is a plenum of sorts to allow air to flow into the ducts, Unfortunately this area seems to garner little attention to detail by manufactures leaving the insulation and bare metal exposed. When the old units were remover I re-secured this area with aluminum tape designed for HVAC sealing. That can be easily bought on line or most hardware or big box stores. U used pieces of a pool noodle from Dollar Tree to fill large gaps and provide padding on sharp metal edges before covering all in Al tape. I believe this also improves air efficiency and may contribute to noise reduction.

It is probably possible to use the original bolts and pass through the roof unit and secure them from the top with a nut and washers. I had discussed this option with the installer but he was concerned the roof unit might move when exposed to travel forces since the 1'4" bolt is smaller in diameter than the M8. Also using a smaller than designed bolt might void the warranty or even create a liability issue should there be an "issue" down the road. This was plan B is w could not find a M8 solution. If I were doing myself it probably would have been the easier solution to use the plan B but he had liability to consider.  

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I'm in the market for a new unit right now. Last summer I did a rapid replacement of my original penguin with a DuoTherm Brisk II (cooling only). It was nice for a year. It IS louder than the Penguin in the front.  Although it is 15K where the Penguin was/is 13.5. The Brisk has now become a Brick as it has stopped cooling. With summer coming quickly. I'm looking for something that can run  a full ducted system.

I got most of the info I need here but I'm missing something important. I have a Furnace that is AWESOME in deep winter (Although it has just started showing signs of issues (Going to have to fix it). I want to know how the Houghton hooks up to the controllers and can It work in conjunction with the Furnace?

I'm assuming, the two units could be run independently with the supplied remotes and then turn them off when running the furnace. Seems like it would work. Open to other ideas here.

Thanks for the writeup! You've sold me on the units. Just need to work out details before purchase.

ALSO. How did you wire it? does ith plug in directly to the same plugs? Or is it rewired from the feed wire for the old unit?

 

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FYI... The "thick roof" mounting kit for about $30 says: 

" Includes mounting kit (4 - 7 1/2"L bolts) " 

They may come in handy if the normal bolts included with the unit are too short.... and save trouble trying to make do with something else..

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Cubflyer, The "thick roof kit" is for thick non-duct roofs. This is designed to carry conditioned air from the roof unit to the vents with out loosing air in the roofing material. In a duct system there is a plenum of sorts between the roof top and ceiling. In most rv roofs these are not sealed so the sides are exposed to insulation etc. AA I sealed this area with aluminum foil.

As to the thick roof kit. I had spoken to RecPro prior to the purchase and was told that those parts are included in the 3800 and 3400 unit kits. In my case I did receive 4 - M8X1.25 X 7-1/2" (190mm) and the gasket. The distance from the inside bracket, through the washer and oblong metal bar to the bottom of the roof unit once set on top of the thick roof gasket is about200, It is not much difference, about the thickness of my finger, so probably twice that as a minimum requirement to secure the unit. We tried to compress to foam gasket to clear the gap but it was not possible, in our situation.

NVRtoofast, I can only speak to my situation so YMMV. That said, the Houghton units do not connect to the existing controler or any wall mount contriller for the furnace(s). In our case we have two LP furnaces, each controlled by a controller box in the original Duotherm. The Houghton units are controled by the remote control or the defusser control. In our case we left the wiring connected to the the controller and the wall mount thermostat and secured the controller box on the inside of the plenum. So the wall mount thermostat controls only the LP furnaces while the remotes control is used for the the a/c and heat pump.

As an aside, now that I have had the two Houghton units running continuously for 48 hours in southern Florida, I can say that our experience is more like a residential central unit than a typical RV a/c. If quiet is what you are seeking this is as close as I have seen to a mini split.

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I think in many/most applications they probably are long enough. In our particular coach they were not. My suggestion, if you are considering replacing an existing unit, would be to remove the ceiling grill and measure from the ceiling to the bottom of the twisting roof unit, then add 2". That will account for the gasket and washers etc. If it is more than 7.25" plan on needing longer M8 bolts or some other modification.

Nvrtoofast, the only wiring from the original system that needs to be transfered is the 12ga romex(110vac).

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10 hours ago, 1nolaguy said:

Nvrtoofast, the only wiring from the original system that needs to be transfered is the 12ga romex(110vac).

Understood. Makes sense and thank you.

Looking through comments on the RecPro site for the unit i ran across a comment that mentioned using: https://www.switch-bot.com/ to manage two units through individual thermostats with one controller by the phone. Interesting tech that could be used for other RV applications.
 

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