Carrier 50PG20-28 Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for 48PG20---28: User's information manual User's information manual Installation and service instructions

Carrier 50PG20-28 Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 61 page image

A redLEDisprovidedtoindicatethefunctionoftheboard.Seethetablebelow.LED STATUS FUNCTIONOn Continuously Relay contact closed (normal operation).Relay contact open (phase loss or phaseBlinking reversal has occurred) -- No power will besupplied to the control system.Off 24 vac control power not present (off).Thermistor Troubleshooting -- The electronic con-trol uses thermistors to sense temperatures used to controloperation of the unit. Resistances at various telnperatures arelisted in Tables 50 and 51. Thermistor pin connection points areshown in the Major System Components section. The generallocations of the thermistors are shown the Major SystemComponents section.AIR TEMPERATURES Air temperatures are measuredwith 10 kilo-ohin thermistors. This includes supply-air temper-ature (SAT), outdoor-air temperature (OAT), space telnperaturesensors (T55, T56, T58), and return air telnperature (RAT).The supply air temperature (SAT) and outdoor air tempera-ture (OAT) thermistors use a snap-mount to attach through theunit sheet metal panels. The snap-mount tabs must be flattenedon the tip end of the sensor to release _br relnovat from thepanel. See Fig. 13. To reinstall, make sure the snap-mount tabsextend out.REFRIGERANT TEMPERATURES Condenser coil tem-peratures are measured with 5 kilo-ohin thermistors. Thesemeasurelnents provide an approximate saturated condensingtelnperature tbr each circuit (SCT.A, SCT.B). Ensure that ther-mistors are placed at the correct location and axe snapped se-curely over the return bend so that contact is made between thethermistor and the tube.THERMISTOR/TEMPERATURE SENSOR CHECK Ahigh quality digital volt-ohinmeter is required to perform thischeck.1. Connect the digital voltmeter across the appropriate ther-mistor terminals at the J8 terminal strip on the Main BaseBoard (see Major System Components section).2. Using the voltage reading obtained, read the sensor tem-perature fiom Tables 50 and 51.3. To check thermistor accuracy, measure temperature atprobe location with an accurate thennocouple-typetemperature-measuring instrument. Insulate thennocou-pie to avoid ambient temperatures tioln inlluencingreading. Temperature measured by thennocouple andtelnperature determined fiom thermistor voltage readingshould be close, within 5° F if care was taken in applyingthennocouple and taking readings.Table 47 -- Gas Heating Service AnalysisPROBLEM CAUSE REMEDYBurners Will Not Ignite. Active alarm. Check active alarms using ComfortLink TM Scrolling Marquee.No power to unit. Check power supply, fuses, wiring, and circuit breakers.No power to IGC (Integrated Gas Control). Check fuses and plugs.Heaters off due to time guard to prevent short cycling. Check using ComfortLink Scrolling Marquee.Thermostat or occupancy schedule set point not Check using ComfortLink Scrolling Marquee.calling for Cooling.No gas at main burners. Check gas line for air and purge as necessary. After purging gasline of air, allow gas to dissipate for at least 5 minutes beforeattempting to re-light unit.Water in gas line. Drain water and install drip.Inadequate Heating. Dirty air filters. Replace air filters.Gas input too low. Check gas pressure at manifold. Refer to gas valve adjustment onpage 90.Thermostat or occupancy schedule set point only Allow time for W2 to energize.calling for Wl.Unit undersized for load.Restricted airflow.Too much outdoor air.Limit switch cycles main burners.Poor FlameCharacteristics. incomplete combustion (lack of combustion air)results in: Aldehyde odors, CO, sooting flame, orfloating flame.Burners Will Not Turn Off. Unit is in Minimum on-time.Unit running in Service Test mode.Main gas valve stuck.Decrease load or increase of size of unit.Remove restriction.Check economizer position and configuration. Adjust minimum_osition using ComfortLink Scrolling Marquee.Check rotation of blower, thermostat heat anticipator settings, andtemperature rise of unit. Adjust as needed.Check al! screws around flue outlets and burner compartment.Tighten as necessary.Cracked heat exchanger, replace.Unit is over-fired, reduce input. Adjust gas line or manifold_ressure.Check vent for restriction. Clean as necessary.Check orifice to burner alignment.Check using ComfortLink Scrolling Marquee.Check using ComfortLink Scrolling Marquee.Turn off gas supply and unit power. Replace gas valve.61