Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
38
Hunting Superheat
NOTE:
Hunting is when the valve superheat swings more than 10°F
Superheat in repetition. This is typically an application issue.
20. Check for obvious kinked or pinched distributor (capillary) tubes
causing imbalance to the circuiting.
• If OK proceed to Step 21
21. Check that proper size valve is used per Product Literature.
• If OK proceed to Step 22
22. Check airflow, sensing bulb tightness, orientation on vapor tube
and ensure bulb is properly wrapped.
• If OK proceed to Step 23
23. Check for even temperature distribution (15 degree range between
circuits) at outlet of each circuit of evaporator and for even air
distribution over all evaporator slabs
• If OK proceed to Step 24.
24. Move sensing bulb further down suction line.
• If problem not corrected, replace valve
Pseudo Evaporator Superheat Instructions
The Pseudo Evaporator Superheat calculates the superheat at the outlet
of the evaporator with known and available information. Because there
generally is not a pressure port on the vapor line at the indoor coil, this
procedure allows the service personnel to evaluate the evaporator
superheat with the vapor pressure port at the outdoor unit.
The method requires the following information:
• Suction line temperature at the outlet of the evaporator (°F).
• Suction line pressure at the outdoor unit (psig).
• Outdoor nominal unit size (btuh).
• Suction line equivalent line length (ft).
• Suction line pressure drop from tables (
).
• Pressure-Temperature relationship for refrigerant used (P-T Chart).
If system uses a vapor line the same size as vapor service valve fitting or
larger AND the line set equivalent length is 80 feet or less, the pressure
drop in vapor line of line set can be ignored.
1. Take suction line temperature at outlet of evaporator at indoor unit.
2. Take suction service valve pressure at OD unit.
3. Determine lineset vapor line equivalent length and tube diameter.
4. Determine suction line pressure drop from
(R-22).
5. Calculate Pseudo Evaporator Superheat.
• Add the suction line pressure drop to the pressure reading obtained
at suction service valve.
NOTE:
For nominal and larger diameter vapor lines with standard
length linesets (vapor line same size as service valve fitting size and
larger with equivalent length less than 80 ft) the pressure drop can be
ignored – use vapor service valve pressure and evaporator outlet
temperature to calculate superheat
• Determine saturated evaporator temperature from a refrigerant
pressure temperature relationship chart (PT chart).
• Subtract saturated evaporator from evaporator suction line
temperature to obtain evaporator superheat.
A01058
Fig. 37 – Tube Fitting Geometry
Table 5 – Fitting Losses in Equivalent Feet
TUBE SIZE OD
(IN.)
90° STD (A)
90° LONG RAD (B)
45° STD (C)
1/2
1.2
0.8
0.6
5/8
1.6
1.0
0.8
3/4
1.8
1.2
0.9
7/8
2.0
1.4
1.0
1-1/8
2.6
1.7
1.3
