Question about Coleman Mach III Air Conditioner
I recently purchased a caravan with a Coleman "Mach EL RV Series" airconditioner. The unit on top of the van has written on it "Mini Mach".
When I turn it on, it seems to fire up OK, but does not produce any cold air.
The unit was made in the USA in 1982. Heats fine, blows fine - just doesn't cool. I left it going the other day for an hour or so but to no effect.
Any thoughts would be appreciated.
1.The selector switch may be open.
2. Thermostat may be open.
3. Overload switch may be open.
4. Compressor winding may be open.
and rotate the switch to the proper position and read
continuity as follows:
Terminals Switch Position
L-1-3 Lo Heat
L-1 Lo Fan
L-2 Hi Fan
L-1-4 Lo Cool
L-2-4 Hi Cool
The compressor motor is located inside the hermetic
compressor housing and therefore not accessible for service or
visual observation in the field. However, the motor winding
condition can be analyzed by using an ohm meter. Be sure to
remove all the leads from the compressor terminals before
making this check.
1) If the resistance between any two terminals is 0
ohms, the motor windings are shorted.
2) If the resistance between any terminal and the
compressor housing is anything but infinity, the
winding is grounded.
3) If the resistance between any two terminals is
infinity, the winding is open.
On a good compressor, the highest resistance will be between
the R (run) and S (start) terminals. The lowest resistance will
be between the C (common) and R (run) terminals. The
intermediate resistance will be between the C (common) and
S (start) terminals. Notice that compressors have the
identification of the terminals marked on either the terminal
cover or on the compressor housing.
There are several capacitor test devices available. The ohm
meter is one of them. The ohm meter cannot verify a
capacitors MFD (microfarrad) value. However, the following
procedures will show you how to use an ohm meter to
determine if the capacitor is good, open, shorted or grounded.
Before testing any capacitor, always perform the following
* This test must be done with a analog type meter.
a) Disconnect all electrical power to the air conditioner.
b) Discharge the capacitor with a 20,000 ohm (approx.
3 watt) resistor or larger.
c) You may discharge capacitors with a standard volt
meter if you use a scale over 500 volts and touch the
leads (one lead to each side of the capacitor). The
volt meter will discharge the capacitor.
d) Identify and disconnect the wiring from the
e) Set and zero the ohm meter on the “highest” scale.
When testing for a good, open or shorted capacitor,
perform the following checks: Place the ohm meter
leads across the capacitor terminals (one lead on
each terminal) and perform a continuity test. Then
observe the action of the meter needle or indicator.
Reverse the leads and test again. The result should
be the same. Note: If the capacitor had not been
properly discharged, a false reading could be
indicated on the first test. Always test several times
(reversing the leads with each test). This will verify
the capacitors condition.
If the capacitor is good, the indicator will move from infinity
(the left side), towards zero ohms and slowly return back to
infinity. Reverse the leads and test again. The result should
be the same.
Most models use a start capacitor and a start relay to give the
compressor high starting torque. The compressor will,
therefore, start against normal pressure difference (head
pressure minus suction pressure) even when shut down for a
short period of time. The start relay will disconnect the start
capacitor when the motor reaches approximately 75%
Start (Potential) Relay
The start relay consists of –
1) Normally closed contacts internally between
terminals #1 and #2 which switch in the start
capacitor in parallel to the run capacitor during shut
down and then switch out the start capacitor when
the motor reaches approximately 75% normal
2) A high voltage coil internally between terminals #5
and #2 to actuate the contacts. The coil is too weak
on line voltage to actuate the contacts, but it is
connected in series with the start winding and it gets
the generated voltage of the start winding portion of
the compressor motor. This generated voltage is
much higher than line voltage and varies with the
speed of the motor. Therefore, since the relay is
designed to open the contacts at 75% of normal
running voltage (measured between terminals #5 and
#2), the contacts will open (thus disconnect the start
capacitor) at approximately 75% of normal running
(B) Positive Temperature Coefficient Resistor
(Commonly Known As PTCR Start
The resistor acts like a potential relay in that it takes the start
capacitor out of the start circuit, but uses resistance of
electrical flow (back EMF from compressor) instead of
opening a set of contacts. The service person should be careful
handling the resistors. They will be hot during operation (up
to 160 degrees F). The air conditioner needs to be off for 3-5
minutes during cycle time and when servicing to let the
resistor cool down.
That covers everthing.
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Posted on Feb 09, 2009
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Posted on Jan 02, 2017
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