Rheem trouble

Mr. Blonde

I haven't been back because the customer was leaving for vacation. There due to return today. I'll post more later.
thanks

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Mr. Blonde

I'm working on a 4 ton Rheem system that has low suction. Furance is a Rheem with a 5 ton drive. Suction preassure is 58 to 60 with 53* suction line temp. Discharge is 180 with 82* liquid line temp. Indoor ambient is 75* and outdoor is 75*, delta t of 18*. I removed the plenum door at the evap. and the furnace door for the blower to check for airflow issues and no change. I removed the TXV bulb and suction came up to 67, suction line temp. went down to 40*. I thought that i had a txv that wasnt feeding enough refrigerant. The unit was low when I started and I found that the evap. was leaking so I thought it coudn't have worked out any better. I replaced the coil with another Rheem unit that had the txv factory installed and the same exact problem. The txv is non adjustable. The only other thing that I thought was strange is the condenser is a 10 seer and rheem uses a piston type metering device for these with there 12 seer units using the txv. I talked to the rheem dist. and they said that there is no problem matching this 10 seer condenser with the 12 seer evap. Any thoughts?

thanks

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Eugene Silberstein 3

It appears

From the information you provided, you are operating with 19 degrees of superheat and only 13 degrees of condenser subcooling. These are both indications of a system undercharge. Given that the TXV is factory set and non-adjustable indicates that the valve is likely opening wide but still unable to get the superheat down.

Your condenser is presently operating with a deficiency of refrigerant, as is your evaporator.

Techman

Rheem

samoore!The Professor is the Professor!Also try an "electronic sightglass" right at the evap.I try to think as the Professor does,`and I"m right sometimes!and I"m left[behind] sometimes!Real good info by the way!!!!!
Possibly the use of a "hard start kit",with the TXV ,might be needed.

Mr. Blonde

I have raised the subcooling to as much as 30* with only a 1* drop in superheat and no change in suction preassure.I left the unit with 25* subcooling. I thought normally you only want 12* to 15* of subcooling anymore than that and your stacking liquid?

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Eugene Silberstein 3

Typically...

typically we like to see between 15 and 20 degrees of subcooling.

don_163

Sometimes

If airflow is not what it suppose to be high or low will effects your readings.

If it was insufficient airflow everything across the board would be low.
If it was a unbalance heatload everything would be low except subcooling.

What was the wetbulb temp?

Mr. Blonde

My digital sling psychrometer wasnt working so I'm not sure. I know thats what I get for buying a digital unit. I remember that the customer had a digital thermo-hygro and I think it said 40% humidity.I think that might equal around 60* wet bulb?

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jim lockard

A shoelace

and a themometer will give you a wet bulb reading, you can then check a temp chart to get you RH. Best Wishes J.Lockard

Eugene Silberstein 3

I thought

I though I was the only one doing that trick!

jim lockard

one thing

about the Wall, Professor. Keeps you on your toes! Best Wishes J.Lockard

Jim Bergmann_2

Rheem Problem

In order to properly charge the system, the airflow must be correct first. If the airflow is not correct the system cannot operate as designed. Normal subcooling for that unit is 8-12 degrees. You have it overcharged at 20. With a thermal expansion valve your superheat should be measured at the evaporator outlet at the suction line, not the condenser inlet at the suction line. The TXV cannot control the superheat after the bulb. 20 degrees of superheat could be ok at the condenser depending on the length of the lineset and the temperature of the space it travles through. Also removing the return air door would only increase the airflow if the return air were too small or restricted. If the supply were small or restricted the airflow would not change. You need to measure the airflow with all of the panels on and set it first, a 416 mini vane anemometer (testo) would work best for this, then charge the system using the manufactures charging chart on the inside door. There is a charging chart for TXV systems I believe it is based on exactly 11 degrees of subcooling.

For highly accurate quick measurement the rotating vane anemometer is the best way to measure airflow. Vane anemometers have several advantages over any other method. The primary advantages are speed, accuracy, and ease of use. Vane anemometers do not require air density compensation due to air temperature, humidity, or atmospheric pressure. The mini vane allows for a full duct traverse with an automatic calculation of the CFM in the duct if the dimensions are input into the instrument before the measurement is taken. It is imperative that the ducting attached to the appliance, and the base pan, if side returned is used, is sealed. Air leaks up-stream of where the measurements are made will significantly alter the actual reading obtained with this method. If done carefully the measurement error will be less than 3%. Changes in yaw and pitch of the probe head in the duct as much as 10% will result less than 1% error in the measurement making the mini-vane an ideal probe for field air measurement

Subcooling is measured to assure that the expansion device has a solid column of liquid fed to it assuring that metering device will be able to control the load at its peak efficiency. With a TXV the subcooling will follow a manufacturer’s curve based on a given set of operating conditions, or proper equipment subcooling will be listed on the manufacturer’s equipment tag. With a fixed metering device the subcooling is not often measured, as the system is charged from a superheat curve. The subcooling will be a function of the refrigerant in the evaporator.

When charging a refrigeration system, a charging calculator should be used to assure the correct charge. One manufacturer’s chart will work with any brand of equipment provided the same style metering device, and the same nominal airflow are common between them. Manufacturers can have different subcooling requirements for different types of condensers, but 8-10° subcooling is normally the standard.

Steps for proper charging using the testo 523:

1. Inspect filters, evaporator coils, condensers coils and blower for dirt and clean if needed. If condenser is washed, let it dry before charging!!!
2. Make sure evaporator airflow is correct. (400 CFM/Ton AC 450 CFM/ton Hp)
3. Determine type of refrigerant.
4. Determine type of metering device.
5. Measure indoor and outdoor ambient air conditions. (wb and db)
6. Determine proper superheat or subcooling. (Use manufacturer’s chart if available.)
7. Attach Refrigeration System Analyzer (Recording manifold gauge set) to service valves.
8. Attach temperature probe. (To suction line for superheat measurement, to liquid line for subcooling measurement)
9. Verify refrigerant selection in manifold.
10. Charge directly by superheat of subcooling.
11. Verify system pressures and saturation temperatures are within manufacturer’s design criteria if desired.

Kal Row

i was wating for somone to say that...

in my experience - just because it looks clean doesn’t mean it is, especially true if the homeowners are triple f's ( Fried Food Freaks), spray wash'em both down with the green stuff (a mild caustic and soap) - and try setting it by superheat again - think you will be surprised (changes of 15lb on low and 50lb on hi are not uncommon after cleaning)
-all the readings are useless if your heat exchangers are not exchanging heat, could be dirt, grease, a week capacitor, or a dragging motor bearing, fried contactor contacts, and the list goes on, - without proper air volume per sec over clean coils - we are just chasing our tails

- have a friend that lives near the beach, has a few extra sprinkler heads set to wash that sticky salt residue out of his machines twice a day – smart huh? – rheem’s are tuff to wash as you cant get them from well from the outside with their hard metal slot louvered cabinets, you need to aim a hose though the condenser fan to the inside of the coils, but they are more impervious to your neighbors kids playing ball against your machine – I got rowdy kids in my back yard every day and I thank rheem for their cabinet design –they have been abusing this thing for 7 years with no ill effects

Eugene Silberstein 3

I Love Discussing this....

I love discussing this scenario with my students every opportunity I get.

I set the stage by giving them the scenario on our simulation software where the system's operating pressures are low... That's the only information they get...

Many of them decide that, since both the high side and low side pressures are low, the system must be undercharged. So, as the discussion continues, the students decide to add refrigerant until the desired pressures are reached. In the simulator, achieving the "desired" pressures and temperatures is not possible and the "game" continues.

Our "system" had a dirty filter and, as soon as this was found, the system's operating pressures now shot through the roof. High subcooling and almost no evaporator superheat (cap tube system).

I always tell my guys that verifying airflow is task #1.

Without proper airflow, your numbers will be off... could be way, way, way off.

Mr. Blonde

Thanks for the reply. I did check the suction line temp at the evap.I removed the blower door and plenum just to see if I was short of airflow. The fan was set on high for 2000 cfm and after removing the doors I reduced speed to 1600 cfm to see if I was moving to much air and the suction dropped to 56. As I mentioned in the above post the condenser is a 10 seer and the evap. is a 12 seer. The charging chart is for a fixed bore metering device. I thougt about getting the 12 seer chart but I dont know if that would be correct because there normally not matched together. I know that I dont have proper superheat and my suction indicates that I am starving the coil. Thanks for the info on the rotating vane anemometer I will get one.

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Techman

Rheem

Morning all!If the superheat did not change when you added freon which did changed the subcooling up to 30* then back down to 20*,would that indicate a bad TXV or debris in the inlet to the TXV?I removed reed valve pieces from a TXV,installed a filter/drier at the evap,system then ran fine .

Eugene Silberstein 3

How are things going?

We're waiting with baited breath!