Air Conditioning Questions

[tennsmith]

This is my first RV with the luxury of basement-type heatpump and air conditioning system.  I'm baffled by what I see "mechanically" on my coach and have some questions for you guys who have "been there, done that."  First of all, a description of what I see.

My DP (identified below) has a rear-facing radiator and it has two heat exchangers on the sides at the rear.  One of them (right side/passenger side) when viewed from the outside appears to be a heat exchanger with no visible fans and when viewed from below, all I can see is a galvanized sheet metal box with a rectangular hole in it and some hardware cloth over the hole to keep varmints out.  When the A/C is on, air is being pulled through this condenser from outside the coach and exhausted out the rectangular hole in the bottom and I can feel heat in the air flow.  Can't see what is in the box, but the ductwork comes out the rear of the box and goes up into the ceiling at the rear so I assume the evaporator coil and one or more compressors (more about that later) are in this box.  The cold air return is under the bed w/filter in the same area and also enters this box.

On the left side, I see a similar sized heat exchanger from the outside, but this one has 2 electric fans attached to it (on the outside between the heat exchanger and the coach grillwork)  that either blow air through or draw air through the exchanger.  These fans resemble the fans available as aftermarket equipment for auto radiators.  Pancake design, not very deep, several blades and a plastic blade guard.  No box on this side, from underneath I can see the rear of the heat exchanger and attached to the bottom of it is a long cylindrical tube about 1 1/2" in dia, maybe 2" with some sort of "slide" mechanism that could be a "reversing valve" to change from heat pump to A/C.  Nothing else on this side, no sign of a compressor.

The thermostat is one I am sure is made for this type system having an A/C mode, a gas heat mode, and a heat (heatpump) mode.  Cool, not cold, air comes from my ceiling vents when the unit is in the A/C mode.  I'm not sure if it is working "good" or not.  I'm wondering if both compressors are running or if it needs additional refrigerant.  As I read thru the forum, they appear to be "marginal" at best.    Now the questions:

(1)  My EMS panel where it indicates what loads have been shed in reduced power situations, I see A/C compressor #2 listed as one of the things that is powered down, depending on available supply and demand.  Where is this #2 compressor and does it run all the time if not shut down by the EMS?  Why 2 in the first place?  How does one know if both are running?  My EMS panel shows a green light beside all the "sheddable loads" when plugged into 50A service and I assume that that means this 2nd compressor is "enabled."

(2)  I've never seen any action out of the left side heat exchanger/fans.  The fans have never been on.  Tried it again today.  Should they be on all the time?  Do they come on as "reserve" as a function of outside air temperature?  Should they be running when the fan on the other side is running?  Are they linked with operation of the #2 compressor?  Does this side work only in the "heat" mode?  I didn't try that.  Is this thing even a part of the A/C system or is it a transmission cooler?

(3)  Is the cylindrical thingy at the bottom of the left side heat exchanger a reversing valve or something else?

(4)  Is there anything that needs service or maintenance inside the box on the right side and, if so, how in the heck does one gain access to it?

(5)  How does one get a set of refrigerator gauges on this beast to tell  if it is low on refrigerant or not?

Those are my questions for now....maybe when I know more, I'll have more questions.

Thanks

 

[Utclmjmpr]

The cilindrical thingy is probably the dryer, in series with the condenser.>>>Dan

 

[tennsmith]

Dan, it has an inner cylindrical rod-looking "slide" that appears to have about a 3" travel and maybe 5/8" in diameter.  Lots of hoses going to whatever it is.  I figure the slide position determines what hose is connected to what hose, etc. to reverse the heating/cooling cycle.  Heck, it could be some other gizmo/gadget....I don't know beans about what I'm looking at. 

 

[Utclmjmpr]

Well by your discription its not the dryer for sure, I'm not  up on heat-pumps.>>>Dan :-\

 

[Ghostman]

Bob,
To start I have never seen this set up in a unit before. I do know how a unit similar to what you are describing works though.( in a home).  A heat pump is to help supplement the furnace in the winter. How this works is reversing the operation of your AC unit. When this happens your evaporator and condenser changes rolls. Everything still operates the same it just reverses the action of the system including the fan on the outside condenser changing direction. If you think about it in the summer when you go outside and feel the fan it is producing warm air. In turn this is removing it form interior. So if you reverse the system flow this in turn will produce warm air in the inside instead of cold. If it gets cold enough to where the heat pump can not keep the temp up to what your thermostat is set at the furnace will kick on to take over. When you are using your AC the Heat pump plays no role. The difference of ambient air temp if measured form your intake to the closest discharge vent from your ac should be around 15-20 deg cooler. This is the most a AC unit can change the temp. If your unit is 95 deg the are should be coming out around 80 deg. As far as the other questions you had on what you were looking at I am not sure without being able to see.  Hope this helps some.

 

[Gary RV_Wizard]

Your a/c should be able to reduce the ambient (inside) air temperature by 20-25 degrees as the air flow through. That means you should measure the air at the outlet duct nearest the a/c and see a 20-25 degree reduction at that point. If it isn't getting that much cooling, you have an a/c problem.

The reason for two compressors is just what you observed - the ability to run on a 30A shore power hook-up. By using two smaller compressors instead of one big one, it can shed load (the second compressor) when only 30A is available. This is analogous to having two roof mount a/c's rather than one big one.

I've heard some war stories about getting access to the basement a/cs to work on them. Apparently it is difficult at best in some models and therefore expensive in terms of labor. From what I've heard, some shops simply(?) remove them from the coach to do any serious work. I wouldn't want to pay that repair bill!

We have plenty of Winnie/Itasca owners here, so somebody should have some basement a/c stories to tell.

 

[tennsmith]

Thanks Gary, I'll put a thermometer in one of the rear vents closest to the unit and see what temp air I am getting.  It is definitely "cooler" than ambient but far from what one can feel in an auto A/C.  Mostly I am trying to find out if my 2nd compressor is working at all.  Seems that if it was, the other heat exchanger should be doing something, assuming that is what it is.  I do know my unit is a RVP brand if that helps anyone.

 

[Gary RV_Wizard]

RVP (RV Products Inc) is the manufacturer of the Coleman Mach brand of roof a/c's. Good outfit. The basement a/c they sell under the RVP brand name.

http://www.rvcomfort.com/rvp/rvp.php

 

[Neal]

Thanks Gary, I'll put a thermometer in one of the rear vents closest to the unit and see what temp air I am getting.  It is definitely "cooler" than ambient but far from what one can feel in an auto A/C.  Mostly I am trying to find out if my 2nd compressor is working at all.  Seems that if it was, the other heat exchanger should be doing something, assuming that is what it is.  I do know my unit is a RVP brand if that helps anyone.

On mine, if you are running on the generator, the EMS will display the total amp usage of the coach. If you look at what the amp usage is, then turn on the air conditioner, after both compressors come on, I would think the amp usage would go up around 25 amps. There is probably a time delay between compressors coming on.

 

[Neal]

(4)  Is there anything that needs service or maintenance inside the box on the right side and, if so, how in the heck does one gain access to it?

(5)  How does one get a set of refrigerator gauges on this beast to tell  if it is low on refrigerant or not?

Those are my questions for now....maybe when I know more, I'll have more questions.

Thanks

On mine the outdoor coil is the heat exchanger on the passenger side at the rear. The whole air conditioner is enclosed inside a box at this point.  To get to the controls & check freon, you hinge up the panel that contains the grill for this outdoor coil. Then there is a panel to remove that exposes all the electrical controls. & some where close by are the refrigerant taps.

 

[tennsmith]

Thanks Neal, I'll look into access via that route.  Question, do you have another coil on the driver side?  If so, what is it for?  Transmission cooler?

 

[Neal]

Thanks Neal, I'll look into access via that route.  Question, do you have another coil on the driver side?  If so, what is it for?  Transmission cooler?

No, the drivers side coil is for something else, I did know, but am having a senior moment. The evaporator coil is inside the box that contains all of the air conditioner. I have not had my air cond out, but read instruction, along with pictures, I think on this web site, where someone had to change a blower. It did not sound to difficult. Mostly like working on any selfcontained package unit.
We printed out a manual from www.rvcomfort.com/pdf_documents/1976408_copy10.pdf, the manufacturer.

We were able to make a couple minor changes, trying to get more cooling. Increased filter area at return from about 16x16 to 20x25. Increased return air grill size. This will tend to decrease static pressure & increase air flow, which normally increases cooling capacity. We also made foil covers styrofoam window covers that snap in, when needed on extra hot days.

 

[tennsmith]

Neal, I had a senior moment myself.  I'm pretty sure that the coil on the left side is for the dash A/C.....finally came to me.

 

[dfdcaptain]

Bob;
Two tips.  When this unit gets to one degree of the set point it drops out one compressor and the remaining compressor is not able to cool the coach down to the set point.  As a result the unit will keep running and the second compressor will cycle on and off as the temp. rises and falls.  You can over come this by setting the temp a few degrees lower than the desired temp.  Also check the plenum that sends the cooled air up to the duct work that supplys the coach.  It is behind the rear cap on the coach and can be seen from beneath the coach looking up towards the roof.  These units are prone to the tape failing that seals the seam in the plenum , end result is more cool air goes out the opening than in the coach.

 

[Neal]

Neal, I had a senior moment myself.  I'm pretty sure that the coil on the left side is for the dash A/C.....finally came to me.

One other thing that is different about this heat pump versus a house heat pump, is that it does not have the same type defrost cycle. When it needs to defrost, it just shuts down & goes to gas heat. Also turns on gas heat for 2nd stage on t-stat under some conditions. There are times we would rather not burn our gas, so we put a switch it the white control wire to the gas heat, so we can keep it from coming on when we desire.

 

[tennsmith]

Great idea on the setpoint Bunky...I'll keep that in mind and will also check the ductwork (I've seen it back there, but haven't made a check with the system running.