 ICM Head
Pressure Controls
ICM’s head pressure controls regulate system
pressure to help prevent evaporator freeze-ups, low-pressure cutouts and
liquid-slugged compressors in low ambient conditions that can lead to costly
downtime and/or loss of valuable perishable goods. They can eliminate
overshoots common to on/off pressure switch controls and also control
refrigerant circuits. Features include hard start, low temperature cutoff and
high temperature bypass. ICM's head pressure
controls are ideal for air conditioning and refrigeration applications.
Meier
Supply is your complete HVAC/R Wholesaler.
Call
your local branch today!
Superheat
Part 4 of 4
As important as the superheat at the
compressor inlet is, the temperature of the returning refrigerant is also
very important. Most compressor manufacturers state that the return
temperature should not exceed 65ºF.
With this in mind, if the saturated suction temperature leaving the
evaporator was -40ºF and the return gas temperature was 65ºF, this is 105ºF
of superheat. Yes, this is too high of
a superheat. This high superheat would
probably cause the compressor discharge temperature to also be too high.
The compressor must handle heat picked
up in the refrigerant in circulation. The compressor cannot distinguish where
the heat came from. The heat picked up in the suction line causes the overall
system to be inefficient. This will be
the subject of another article.
George Story has been in the HVAC/R industry for 50 years. Most recently George was
the Manager of Customer Training for the Copeland Corporation. In that
position he was responsible for the renowned Compressor Operation and Service
Seminar. Previously the manager of Meier Supply’s Erie store, he currently is
Meier Supply’s Refrigeration, Air-Conditioning and Heating Technical
Specialist.
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TECHNICAL
BULLETIN
February 2006
Lack of Flame Sense
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The heating season
is when we all begin to field some calls from our customers that are
experiencing a problem with one of our Ruud
furnaces. One of the more common problems that the technicians seem
to encounter is a lack of flame sense.
When the furnace goes into a soft lockout the OK light on the IFC will have one blink. Soft lockout is a result of four failed
ignition attempts. So what are some
of the possible causes of failed ignition/flame sense? First we must establish that the power
supply is correctly polarized. Have
the tech test L1 to ground and he should read 120 volt. Common to ground is 0 volt.
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Once it has been verified that
the incoming power is correctly polarized we must establish that the furnace
has been properly grounded. A good ground
is absolutely essential for any
furnace that utilizes a flame rectification system. With flame rectification a small DC current
is generated by the IFC through the burner flame via the flame rod. That is why the burners must be properly
grounded or the flame signal will not be detected. The following is a quick and simple test
procedure to determine a proper ground.
·
Set ohm meter to the lowest setting and then test from
the burners to the common on the IFC. The reading
should be 0 ohms, however 1to 2 ohms is acceptable
·
Next test from the IFC common to ground and once again should read no more than
1 to 2 ohms resistance.
·
The last test is from the furnace ground to a cold water pipe and the reading must
be no more than 1 to 2 ohms.
If the resistance readings check out ok then
pull apart the molex connectors in the furnace
cabinet to ensure that they are dry and clean. Moisture within the connectors may cause a
flame sense failure. Moisture will
sometimes enter the furnace cabinet especially when a drain trap is not
properly installed in the combustion air pipe. This is a problem that will sometimes show
up on a furnace that has been installed for awhile and suddenly begins to
experience ignition failure. Finally,
the technician needs to make sure that the transformer is phased
correctly. Most technicians are
familiar with making sure that the furnace is properly polarized, however
many are not aware that the transformer needs to phased properly. To check transformer phasing simply test
between L1 of the primary and L1 of the secondary. The voltage present should be a result of
L1 primary minus L1 secondary. Ideally
you would read 96 volts. If the
voltage read is L1 primary plus L1 secondary (or 144 volts) then the
technician would know that the transformer needs to phased and he would
reverse the SECONDARY winding
leads only. In conclusion, flame sense
failure can sometimes be a frustrating problem for all of us to figure out so
hopefully I have given some tips that will be helpful in the future. Please contact Steve Post at Meier Supply
if you have any questions.
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