26
Fig. 9-5
ELECTRICAL CHECKS
1. BE SURE ALL THE ELECTRICAL POWER IS OFF TO THE COMPONENT BEING
CHECKED.
2. Remove at least one wire from the component being checked.
3. Measure the resistance of the holding coil with an ohmmeter
4. Measure the resistance across the normally closed (NC) relay contacts.
A. The resistance should be zero (0) ohms.
5. Measure the resistance across the normally open (NO) relay contacts.
A. The resistance should be Infinite (Ğ)
MECHANICAL CHECKS
AIR FLOW
will reveal this problem. With sealed relays, use an ohmmeter to test for open or closed contacts.
A. A specific resistance indicates a good holding coil.
B. Infinite (Ğ) resistance indicates a relay with an open holding coil. REPLACE the defective
an appropriate service part.
relay with an appropriate service part.
B. If the resistance is more than 0.2 ohms the contacts are pitted. REPLACE this relay with
B. If the resistance isn’t Infinite (Ğ),.REPLACE this relay with an appropriate service part.
In relays ,mechanical faults are few. But check relay body for signs of physical damage .
Indoor coil air flow in any air conditioning system is critical. Too much air and the system will not be able
they indicate the cubic feet of air per minute(CFM) moving through the coil. An inclined manometer or
magnehilic guage can be used for measurement.
A velometer measures the velocity of the air in feet per minute(FPM). If the area of duct is known,
1.08 hTEMP RISE
COMPRESSOR AND SYSTEM FAULT DIAGNOSIS
misdiagnosed.To ensure that does no t happen, the technician must determine if the compressor has
problem. The following procedures should help determine if the compressor has failed.
to suffers lack of dehumidify in cooling. insufficient air flow while cooling may result in coil freeze up,
excessive dehumifification and lost capacity.
rrovided to show how to measure pressure drop across the coil. If pressure drop tables are available,
the velometer reading times the area of duct (in square feet ) calculates the air flow.
Checking air flow is the most important diagonistics a service technican can perform. Instructions are
If the indoor unit has an electrical heater, air flow can be estimated by measuring the air temperature
CFM (Electrical Heater) =VOLTShAMPSh3.414
entering and leaving the heater and calculating the CFM.
Compressor manufacturers state that maul of the compressors returned as defective have been
failed or if another control has either failed or stopped the compressor from operating after detecting a
Prior to replacing a suspected failed compresso ˈa thorough check must be made of all existing electrical
electrical components .If not done ,a replacement compressor might also failed or not operate at all
WARNING: THE FOLLOWING PROCEDURES SHOULD ONLY BE ATTEMPTED BY QUALIFIED SERVICE TECHICIANS
EQUIPPED WITH PROPER TOOLS, SAFTY PROCEDURES AND EQUIPMENT AND INSTRUMENTS TO PERFORM
THE DESCRIBED REPAIRS.
Central Air Conditioner Model: Cooling Only, 13SEER units
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