Basement A/C Argh...

Michael - good signature!  8)

I don't recall my return air temp, I always use duct air temp as a measure of performance.  As I recall, the second compressor won't run unless the set temp and room temp have a certain differential, so when I want max cooling, I'll set the temp to the low 70s to be certain both compressors are running.  Otherwise, you only have 12,000 BTUs of cooling  :

Here is a little proof on A/C in and out air temperatures.

    When I entered my RV today (in storage) The inside RV temp was over 100?. I started the generator and started the A/C.. I then affixed a thermometer on on of the ceiling duct outlets (see pix below) and waited.
It took well over an hour to start to feel comfortable inside. I saw the thermostat register 98-98-97 etc. After two hours I took another reading. Keep in mind there was total sunshine all this time beating down on the bus. (Florida).

   The duct output air temp slowly crept down, doors and windows closed. At the 2 hour mark the readings were a shown below.

Room temperature (Intake) was 91?

Duct temperature (Cold blow) was 69?

The difference is 22?  Guess my A/c is working well. If I had waited longer it would have gone to 80 and 60.  80 is fine for me.

How low it will go, I don't know.

carson FL

John Canfield said:

Are you talking about the temps at the outlet ducts?  As I recall, in the summer I'm running in the 40s or low 50s as measured by a non-contact temp gun.  Our interior might be in the high 70s or low 80s, but the air coming out the ducts is plenty cool.

Click to expand...

Yes Im talking about temps at outlet ducts. I see where one poster states 40's or even 30's. Seems like it would freeze. Like I said I've got a brand new unit and I think the best i've got is 52 or so.

For those of you who have measured the duct temp in the 40s, what was your return air temp?

Click to expand...

Just got the following results using my infrared thermometer ...pointing the thermometer into a ceiling duct and holding it there 30-45 seconds until the temp stops going down.

- AC thermostat room temp reads 75 degrees
- Infrared reading at the air intake under the bed reads 73
- First check at ceiling duct, with thermostat set on 75 and one compressor running, the infrared reading was 51 degrees
- I then lowered the set temp to 72. Room temp still reading 75 degrees.
- After I heard the second compressor kick in I again ran the infrared check at the same ceiling duct. Infrared reading was 35.

Based on my readings the past couple of days, and from what I recall in the past, I would guess that the 20 degree differential might apply when only one compressor is running. But as you can see from the above numbers, I get far more than 20 degrees differential when both compressors are running -- right at 40 in the above case!!

afchap said:

I get far more than 20 degrees differential when both compressors are running -- right at 40 in the above case!!

Click to expand...

That's a good test Paul - thanks for the report!  And for those of us with basement air, turn the thermostat way down to get the maximum benefit from two compressors.

Mine is running about what others have reported.  Outlet air is normally about 40 degrees, with both compressors on, though this does vary a bit with outside temp, I have never seen it above 50 degrees, and rarely below 37.  I think this variance is simply the distance the air has to travel on a "Hot" day...  And of course the duct work is in the ceiling and rear cap, which is not the most effective way to "Transport" cold air on a hot day.  These measurements have been made with both a Non Contact IR thermometer, and a Digital Probe, and come up with about the same results.  This is a measurement of Intake Air, Vs. Output air, and there can be as much as a 15 degree difference between the rear most outlet and the front most outlet.

As far as the 20 degree differential, I would also say that is fairly accurate in regard to the average coach temp.  On a 100 degree day in direct sun, I would struggle to get the coach to 75 degrees.  Once the OAT is over 100, it is very difficult to get the inside temp below 78, especially if you started "Hot".  This differential is a measurement of the coach vs. outside air, not intake vs. output air. 

I really do not think I have a "Freon" problem, I believe FrontRange is correct in the the thermistor is most likely bad or placed incorrectly, and is allowing the compressors to continue to run while the coils freeze.  Now lately the humidity is down, as well as the temps more normal and it has been running perfectly.

John

It's been a long time since I've had "refrigerated air" but my parent's house had 2 Tons of a/c and this MH has 2 T of a/c  and the air coming out of the vents is really noticeably cold so even though I don't have any data, I could easily believe the 30-40 deg differential.  We live in a relatively dry climate though and the outside temp rarely gets above 90 so my qualitative information is suspect.  Nonetheless, it works fine.

John (Moder),          Taking your A/C unit out is really not a difficult task.  Get a couple of 5 gal. plastic buckets and put them beside the A/C.  Then get a couple of 2 x 4's to place between the buckets to put the A/C on.  The bolts you mention that will lower the A/C will do the job..........it only needs to come down about 1/4".  Get the screws out of the supply duct L plennum.  Then just slide the A/C out onto the buckets/2x4's.  From there start removing all the screws in the top......about 30 of them.  REmove thte top to expose everything.  Bearings are easy to replace.  Suggest you order a new OUTDOOR blower wheel from RVP to install while you are doing the work.  After all bearings, blower wheel, etc. done start the unit and run it while out of the coach.  The coach wiring will reach without disconnecting.  The hardest part is removing all the screws.

We have a '02 40J so I imagine they are identical in regard to the A/C

KIX 

John Canfield said:

That's a good test Paul - thanks for the report!  And for those of us with basement air, turn the thermostat way down to get the maximum benefit from two compressors.

Click to expand...

Been there done that and still dont get in the 30's or 40's for that matter.

Kix,

Thanks.  Do you need to loosen the rear bolts also?  Or does it "Tip" with just the fronts?

I'll call RVP Monday.  I read Duner's PDF, and I am undecided about the bushings, I see he got his from Granger, and then found ball bearing replacements from there also.  Couple questions on that...  Does Granger sell to Retail now?  Or do you need an account?  I have one close to me here in Dallas.  Also, How gig of a Mod is it to get the Ball Bearing ones in?  I would much rather go that route, as I am certain my bushings are bad, as I can hear both fans making noise, not bad yet, but noise none the less.

John

JLModer2 said:

Kix,

Thanks.  Do you need to loosen the rear bolts also?  Or does it "Tip" with just the fronts?

You need to loosen only the bolts closest to the outside of the coach.  A 3/4" socket with a short extension will do that.  Lower it (loosen) about 1/4".

I'll call RVP Monday.  I read Duner's PDF, and I am undecided about the bushings, I see he got his from Granger, and then found ball bearing replacements from there also.  Couple questions on that...  Does Granger sell to Retail now?  Or do you need an account?  I have one close to me here in Dallas. 


I couldn't get the bearing # that Duner mentioned.  I used bearings I got somewhere else.   

Also, How gig of a Mod is it to get the Ball Bearing ones in?  I would much rather go that route, as I am certain my bushings are bad, as I can hear both fans making noise, not bad yet, but noise none the less.

There is no modification.  They simply replace the originals.

John

Click to expand...

Also, John, if I didn't already suggest it then I suggest that you replace the outdoor blower wheel while you're at it.  Very easy to do.  Significantly quieter outside. 
Hope all this helps you take care of it.  Just get a helper to help get it out and back in.  The rest is a one man, easy job.

KIX

I want to thank all of you for your help.

Pulled it today.  RVP rocks, parts were here already yesterday.  My fans were fine, though I did change the bushings.  I was going to get them from Grainger, but couldn't get them, and decided to just use the OEM ones.  They were not that bad, slightly sloppy, but not as bad as I thought.

Unit was EXTREAMLY dirty.  I am sure it has never been pulled before, but my evap coil (Inside) had at least a 1/4 inch buildup of what looked like cat hair infested dryer lint.  I don't know why it had ANY airflow.  I also replaced both thermistors, which were both bad.  I did get a coil cleaner product from Grainger, and it worked well.  Sprayed in as a liquid, and then foamed up and pushed out the grime. 

I did a full writeup on the blog.  Results are amazing.  This will have to be added to the regular maintenance schedule....

John

Good show John!  And Mark (FrontRangeRVer) wins a free e-case of his favorite adult beverage for a correct diagnosis  ;D

I'd be up for that!  But he needs to come to Texas to get it! 

John

Oh before I forget I wanted to add something about Temp Differential.

According to RVP and several A/C techs I talked to, the difference between the outlet closest to the unit and the intake air should be about 23 degrees measured with a temp prob (according to them the Non Contact thermometer doesn't read accurately enough because you are really measuring the temp of the nearest hard surface...)  I used a Meat thermometer, and my Non contact and got about the same readings though.  What I was told was that a High Difference most likely means a clogged coil and is due to the reduced airflow, and while the air may be colder coming out, it is less efficient and the unit's capacity is severely limited. 

So, if you are seeing high differences (more than 23 degrees F.) you might want to pull, or have your unit pulled and check the coil, it is most likely plugged up.  Before I pulled mine, I measured it at almost 36 degrees difference (intake air at 78, outlet air at 42) this was Both compressors running.  After I cleaned it and reinstalled I was right around 23, but the amount of air and velocity of it was dramatically different, though I have no quantitative way to measure it.

if you are seeing high differences (more than 23 degrees F.) you might want to pull, or have your unit pulled and check the coil, it is most likely plugged up

Click to expand...

Mine has performed with the temp differentials cited earlier since new, and has been pulled 4 times in the six years we have owned it. None of those times did I find the coil particularly dirty or plugged. I have plenty of airflow, and as for efficienty it cools of the MH quite well.  23 is about the differential I see with just one compressor running, but I see much more than 23 with both compressors running.  I would be interested in pushing the question of whether their answer applies to just one compressor, or both at the same time. ...the air flow through the unit is the same with two running as it is with one. Apparently two compressors will make colder air, or they would not have put two in the unit !

AF, I think your correct in that the two compressors running would produce colder air. 

I got this information right from RVP, and it is also in a PDF on their site under the FAQ's section.  I can say mine does run warmer with just one compressor, but I did not take a actual temp.  From there literature, talking with the CSR at RVP, and talking with a couple independent techs, I am confident my unit is operating in specs, but that doesn't mean it is the same as all?  I am simply not that smart to answer that!

I can say mine must have been degrading in performance for quite a while since it has never cooled the coach as quickly as it has today.  Today wasn't an extremely warm day, but it did get 92, and I am in almost direct sun with high humidity, before it would not have kept up even in this weather and would have most certainly been running constantly, today it easily kept 70 in the coach and cycle all day, even in the hottest part of it.

What kind of air filter are you using? The "cat hair" clogging up the coil really concerns me.    Only buy those cheap blue fiberglass ones...the kind that you can see your hand through...buy a dozen of them so you have spares, and change them once a month or so.....

Also, YES, running two compressors will double the BTU output.  Sometimes if it's not that hot outside, I flip off the breaker to the second compressor and only run one compressor so we wont get the coil freeze up problems that occur with our unit.

So far so good, haven't had a freeze up since the R&R, and I have been pushing it as hard as I can.

I have been only using the 3M Filters.  I Like the black ones best but they are way too expensive, so normally settle on the Red ones, about 10 bucks a pop.

I pull it out an vacuum it weekly, and change it monthly.  Basically have been doing that since we have owned this coach (about 3 years now.)

It was interesting, the 'Felt" layer on the coil, you could tell when we bought the coach.  Prior to us, there was long brunette hair, and short brilly white hair, then some other pet hair that wasn't 'prince' hair, and finally our hairs and "Prince's".  Yeah, Gross.

I also did some taping up of the joints and such on both the intake and the output side.  The output side I really didn't find any leaks, the intake side I did see where there was some seperation of the plenum near where the top engine cover rests next to it.  I also removed that silly screen infront of the filter and pulled the staples.  The hole isn't finished anyhow, and you can't see it, it was nothing but a cat hair trap and made it hard to remove the filter.  I Layers a couple layers of tape to the filter fit snugly after it slid in, so it shouldn't be pulling anything around the sides anymore...

the 'Felt" layer on the coil, you could tell when we bought the coach.  Prior to us, there was long brunette hair, and short brilly white hair, then some other pet hair that wasn't 'prince' hair, and finally our hairs and "Prince's". 

Click to expand...

It sure sounds to me like return air is bypassing the filter. On my 40e, the filter is under the closet floor. It lays horizontal in a metal frame with little if any chance for air to bypass it. Most of the return air passes through a grate at the foot of the bed, but air also goes under the edge of the bed on the closet side and through a small grate under the washer/dryer where it can pass under the closet floor. Technically, that small grate is the return air for the bedroom LP furnace, but it is not closed off to just the furnace.