Heating, Air Conditioning, Fridge, HVAC/Carrier AC cool but no heat


QUESTION: Hi Joseph, I am myself an ex Army Aircraft technician, Helicopters, turned Fridge tech 3 years ago. I have a carrier ducted system with R22 so quite old. She runs on cold fine, but when on heat she runs for 1min then shuts down. I have recovered and refilled fridge with correct amount, there are no hi or low Px switches on this system. The wall thermostat and internal PCB are new. any ideas? Many thanks Peter

ANSWER: Peter,

Taking this is a Heat Pump? If so typically low pressure switches are mounted on the inside of the outdoor unit liquid line. They open mainly when system is extremely low on charge or no charge in the system. Check to make sure your indoor coil is clean and not restricted,as that is the condensor in heat mode, you may be tripping on internal overload of the compressor,due to high head pressures from a dirty indoor coil which also raises the running amps. if your positive there is no pressure switch. look at wiring diagram to see what is in series with the compressor contactor and you would need a meter to troubleshoot the control system. Check to see what safety controls you have. If you have a biflow filter drier you may be partially restricted in the heat mode.Touch each side of the drier, it should be the same temperature on each side,if the outlet side ( during heat mode ) is colder you probably have a partial restriction. You do not mention any refrigerant pressures,or compressor run amps to compressor designated run amps. You can bypass the the t-stat by jumping at the outdoor unit ( one piece packaged unit ) by jumping R to Y to O to G , if this is a two piece system jumper those points at the indoor unit. see if your heat stays on longer than one minute.Does the blower fan continue to run when the compressor shuts off after the one minute period, It should.

In closing find what is in series with the compressor contactor , there should be some type of safety control to protect the compressor. Check for 24 volt ac at the compressor contactor coil then determine where your loosing it.your pressures should be on average 45 PSI suction , certainly higher or lower depending on OD temps.head pressure varies ,from 170-250 .Those are general pressures reading only.

After answering your question, I looked at the question pool, you described a completetly different set of problems for the same unit ( dated 26 Feb. ) reading your pool question sounds more like electrical miswiring than anything. suggest downloading a wiring diagram of your unit if you don't have one attached to a inside panel on the outdoor unit and check each wire connection to the wiring diagram

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QUESTION: Hi Joseph, thx for getting back to me, the previous problem with wiring is now eradicated, a single pole switch was being used, I have now installed a dual pole, thus compressor and fan can be controlled separately.
So I have double checked the wiring diagram and what is on the unit, low and High px switches were an option, these have not been fitted. All filters and coils are clean and free. The only sensors I can find on the system and wiring diagram are. 1. internal coil temp thermistor B4  2. Internal "Air On" thermistor B3.  3. External Coil Thermistor S1&S2. I shall check to see what filter driers are fitted.


If these are thermisters , you would have to know the resistance reading that corresponds with the temperature reading its sensing. That would be hard to determine.If this is a heat pump then you  should have a defrost thermostat attached to the outdoor coil, that is a switch not a thermister and can be checked with a meter. That only controls when too initiate and terminate a defrost, it should not have anything to do with the unit shutting down after one minute.Double check for any check valves if this is an older heat pump,they were somewhat common on the older models.You also may have issues with the metering device for the heat cycle.As you know there are two metering devices on Heat Pumps.

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.


Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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