If my line-set is undersized what problems could this cause?

many factors can cause excessive condensation on your unit. the BIGGEST problem with air conditioners is when ducts are undersized or the unit is simply too big. You didnt post what type of unit you have but airflow is critical. Clean filter, clean drain line, and a good seal around all unit penetrations along with good airflow and you should be in much better shape!! Hope this helps!!

Set an undersized heater thermostat to any temperature you want - if undersized, it will not be able to get to the set temp if it's cold ...

Shut downs with new heater might be defective PC board.
Other issues could be associated with improper installation.
Low gas pressure caused by undersized gas meter or water in the gas line, undersized gas line to unit (requires 1" gas line to within 10 feet and then 3/4"), wrong type of gas line (cannot use flexible gas line), improper vent (for example too long horizontal run or undersized vent pipe or shared vent with furnace or other gas appliance), not enough incoming fresh air supply, nearby exhaust fans or vent fans stopping proper draft on tankless, temperature set too high for cold incoming water supply (install tempering tank to help preheat water),..
http://waterheatertimer.org/Tempering-tank.html

Other causes can be clogged water filter located where cold water enters tankless, or clogged water line, or crossover caused by bad single-handled faucet or bad crossover valve on recirculation system, improperly sized recirculation system. These problems can mean less water flow through tankless, so burner shuts down, and unit throws error code because sensor indicates water flow is still moving but inadequate to trigger burner
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/Water-heater-recirculation-system.html


Gene
Water Heater Timers Save Money

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

An undersize suction line decreases the capacity, and causes the compressor to work harder and more frequent starts. It may even experience low suction pressure and high superheat.

Undersized gas line. Water in gas line. Low gas pressure.
Copy following links:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://waterheatertimer.org/How-to-install-gas-water-heater.html
http://www.thetankatwaterheaterrescue.com/forums/forum3/

gene
h

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

a high pitched whistle is a gasflow problem. usually caused by the techs who installed the heater who didnt ensure proper gas pressure supplying that heater. undersized gas line, or gas meter too small

Likely two very separate problems:

Prime failure is either mechanical wear in the pump or an air leak in the suction line. It is usually easier to look for air leaks in the suction prior to disassembling the pump to look for trouble. A clogged foot valve, a clogged impeller, clogged inlet screens, etc.

Line leads discoloring can mean many things: Line voltage may be dropping too much and/or the line leads undersized. The motor may be beginning to fail causing an increase in amp draw. The pump may be overloaded but that is unlikely.

As you narrow down the possibilities please add comments to this post if you need additional guidance.

John

the ignition control is not rectified for flame change it

Try these:

1. Check the water dispenser arm. It must have some resisting force when pushed or pulled. Otherwise it is defective, then replace it.
2. Check the water line and water inlet valve for clogging. It can cause poor water flow, undersized ice cubes and overfilling. Replace if found defective.
   

Note: The ice and water dispensing system of your refrigerator is complex. Aside from simple problem of a leaky water tube or a jammed ice chute, most other components are not user serviceable. Service of a qualified appliance repair technician is suggested for such repairs.