Rheem R410a System

[dash]

If the return temperature is the same ,at the grille and the inlet to the equipment ,in the heat of the day ,there likely minimal return leakage .

[docholiday]

2 stage huh? This might just splain something.

Can I ask you for a model and serial number of both the outdoor unit and the furnace? Here's why. Rheem did not make a 2 stage a/c unit up until recently but their furnaces would accept one if it were made by another manufacturer. Most of the other brands have a 100% and 50% capacity. Therefore the furnace board used these numbers to control the fan. However, when Rheem developed their 2 stage unit, they had to change the logic in the furnaces because thier 2 stage a/c capcities were 70-100 and the furnaces would not control 70-100. The furnaces have been changed but who knows when the furnace you have was built. It may have been just prior to the change and this may be whats happening here.

Post model and serial numbers from both furnace and a/c. (the serial nubmers have a date code in them) Coil would be nice but unless you have that on some paperwork, I wouldnt want you to go opening anything.

[docholiday]

I must also admit I am somewhat concerned as to why the system is running when the return temp is 66 degrees.

[ms7168]

It was running in brief periods and cycling when the return was that cold.

I got model and serial numbers off of the condensing unit and the coil but I cannot locate them on the furnace It must be on the side or back and it is installed in a service closet so I can't see them. I looked all over the front and behind the two removable front panels. It says on it Rheem Criterion II Plus 2 LXE Gas Furnace and it is a 75k btu model. I am uncertain whether it has a 1/2 horse or 3/4 horse fan motor but I'm guessing 1/2 because of the playing around with the CFM's. The 1/2 horse has a top speed of 1200cfm and the 3/4 has a top speed of 1600cfm.

The air conditioner is model RAML-036JAZ and Serial 6575-M1801-17109 and the coil (this is on the front of the case it is in) is model RCHL-36A2GG21 and Serial T1901.

All three were purchased on the same day from the Rheem Distributor and supposed to be for each other. The air conditioner and the furnace have similar cases and match each other.

I was led to believe it does 80 / 100 but it could be 70 / 100.

It's cooler in here today. The temperature outside topped about 96 today so the unit has only slipped a degree (so far). The supply dry bulb temp is currently 60 and the return is 71.

[docholiday]

The RAML is a single stage air conditioner. The furnace is two stage variable speed. Your really do have a nice set up.

Ok here is my suggestion.

Have a two stage cooling thermostat installed (you may already have one since your furnace is two stage). Have the technician wire the second stage cooling to the ODD terminal and configure the dip switches to ODD. This will allow you to run at the 15% lower airflow when the system capacity is holding the temp giving you the better latent capacity. The other switches (switch 1 and 2) should be set to provide nominal airflow. When the load calls for second stage the fan speed will jump up to full speed to handle the sensible load. This, will actually make your single stage unit run like a 2 stage unit, something like 85-100.

The ODD stands for On Demand Dehumidification. In most cases a humidistat would go here but this is actually a little better for an application like yours.

[docholiday]

BTW, the sticker is inside the removable pannels but on the side, hard to see without a light. I dont need those numbers, I thought maybe we were talking about a new system.

You're system is a perfectly acceptable match built in 2001.

[ms7168]

Coolies

I have a two stage thermostat already (2 cool and 2 heat)
It will either say Cool 1 or Cool 1 & 2. I am not sure how it is presently connected. I considered adding a humidistat but the setup you suggest is even better.

The thermostat is a White-Rodgers 1F81-71

[ms7168]

I called the service tech today. He said "put it back on 1200cfm, if you just must go ahead and cut it back 15% but I think it's only going to raise your bill and not net you any better results."

I told him I would try it. I put thermometers on the furthest supply outlet and the return and watched them all day. I've also observed the temperature and humidity in the house. Guess what? It does the same thing on full speed as it does on 1020cfm. Except there is more air moving so it makes it feel a little cooler. And as bad as I hate to admit it the humidity is decreasing at a faster rate than before.

He said that if I really wanted him to he would come out and hook the second stage cooling to the ODD but he would have to consult with the supplier first to get the instructions on doing it because NO one has ever done it here before. He also said it would be $80. for the call.
I told him I would think about it.

[dash]

If Doc says it's not a two stage,I bet it's not a two stage.

Hang in there and find the problem.

[docholiday]

I think he understands its not a two stage cooling system. What I was referring to was a means to make it work like one. Unfortunately, I cant break the rules and spell out the detailed instructions in this forum.

His tech needs to talk to his distributor service rep.

[dash]

Oh ,I see now ,said the blind man.LOL

[ms7168]

Thanks guys I appreciate it.