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Delay Timers and the Air Conditioner Condenser - Air Conditioners are big HVAC refrigerators. Air Conditioners and Heat Pumps use the HVAC refrigeration cycle to transfer heat from a place where it is not wanted (inside absorbing heat with the evaporator coil) to a place that makes no difference (outside using the condensing unit)(in the cooling cycle). The heart of any HVAC air conditioning, heat pump, or refrigeration system is the compressor that pumps the refrigerant through the HVAC air conditioning system.
When the refrigerant leaves the compressor it is compressed and therefore a higher pressure than it was before it entered the compressor inside the condensing unit. This pressure remains constant (give or take under certain conditions) until it passes through the metering device where the pressure and temperature are reduced. This low pressure remains constant (again give or take under certain conditions) until it again reaches the compressor inside the condensing unit and is compressed again.
Pressure Equalization in the Condenser
When you turn the air conditioner condensing unit off these pressures equalize within five minutes. The equalized pressure is often referred to as static pressure to HVAC professionals. The high side pressure on a hot day can be as high as 300 P.S.I. and higher in some systems. If your HVAC system is not equipped with a delay timer and you turn the system on within five minutes of turning it off, the compressor inside the condenser must start against that higher pressure. That is not good for the compressor and could possibly damage it.
Problem
The HVAC air conditioner condensing unit compressor should not be started unless the air conditioning or heat pump system is at static pressure. I have responded to calls where the air conditioner or heat pump condensing unit was not equipped with a delay timer and the air conditioning or heat pump condensing unit was inadvertently started before the pressures were allowed to become static. Often the compressor inside the condenser is locked up, the run capacitor is shot, a fuse is blown, a breaker is tripped, the compressor is damaged mechanically or electrically beyond repair or a combination of any of these things mentioned.
HVAC Condensing Units and Compressor Mechanics – Delay Timers and the Air Conditioner Condenser
If the homeowner is lucky, the only thing wrong is the capacitor or fuse. The run or start capacitor for your compressor can be replaced for a minimal cost compared to replacing a compressor. If the compressor is locked up there is a chance that it can be unlocked (note the word chance). A hard start kit and a good rap with a hammer can sometimes do the trick. If this doesn’t unlock the compressor then you will have to replace the compressor or the air conditioning or heat pump condensing unit. It is often in the homeowner’s best interest to replace the condensing unit.
Before this happens to you, call the company you often deal with to maintain and repair your HVAC system(s). Ask to speak with the HVAC service manager or HVAC technician that has worked on your HVAC equipment. Ask them if your condensing unit is equipped with a delay timer. They should be more than happy to answer your question…………and if they are not sure ……check to see if the condensing unit is equipped with a delay timer. You may want to have the model number, serial number (for both the condenser and air handler), and type of thermostat you have. Most modern digital and programmable thermostats have delay timers built into them.
Delay Timers and the Air Conditioner Condenser - Digital Thermostats
If you have an older mechanical thermostat it’s a good idea to make sure you have a delay timer in your condenser. Ask your HVAC contractor to make sure you are protected against this problem.
Air Conditioner Service and Repair - another great article to help you from High Performance HVAC
For more on air conditioners click here.
Delay Timers and the Air Conditioner Condenser
Are carrier’s parts always in delay ? is this the right time to select a Carrier for AC replacement ?
I think everything is in delay because of the COVID thing. From my experience, Carrier is like everyone else for getting parts.
Hi: When I had my 2 ton condenser replaced, my ac mechanic thought he was doing me a favor by replacing it with a 2 1/2 ton unit. Now, my house is not properly dehumidified. I’m an electrical contractor and I was told by installing a time delay relay in series with the condenser contactor and delaying the start cycle, I’ll allow the fan coil to drip condensate for a longer period of time and that this may solve the problem. Is this true? Thanks, Dave
Running the fan at a slower speed will create more dehumidification. That is difficult to do without a variable speed ECM blower and the correct solid-state controls. Yes, oversizing will cause humidity problems. This can likely be rectified by changing the metering device but you need someone who really knows what they are doing and can replace the metering device to derate it to 2-tons. Therefore, you will not have to do anything with the fan. High-efficiency systems run the fan at 50% speed or less on start-up to increase the dehumidification process. That translates to more comfort and efficiency. This occurs for approximately 5 to 10 minutes and then it ramps up to 100%. However, that is only achieved with an ECM blower with accompanying controls as noted previously.
With the condenser running the slower fan speed allows more moisture to be removed with the colder coil. Less air moving across the evaporator coil equals less heat hitting the coil allowing it to operate well below the dew point, therefore, removing more moisture from the air.
Also, it depends on the system but there are no guarantees it can be derated or derated efficiently by changing the metering device.
The time delay is not recommended in the fashion you suggest. With no air blowing across the coil you will freeze the coil turning your AC into an ice maker.
I hope you’re still around as I have a question. I had a new system installed in 12/2017. Now when it storms and the power flickers, I get a loud noise coming from my outside units. I called a company out to look at it and they tell me there isn’t a time delay and want to charge me $200 a unit to put them in. I call the orginial AC company to find out why they weren’t put in to begin with and they tell they are not necessary. Yes this is why the AC unit is making a loud noise but it doesn’t cause damage and it has 10 year warranty so any possible damage would be covered.
Now I don’t know who to believe. How necessary are time delays on new systems?
Thanks
If you have a digital thermostat then you most have a time delay. Most of the modern digital thermostats have a built in time delay. The purpose is to prevent the compressor from short cycling. Not sure about the loud bang unless you have a heat pump. Sometimes the reversing valve with cause a loud noise when switching.
the unit in my place was changed in 9/2017 now it goes into delay mode after 20 minutes of running. switched the batteries on the thermostat and also changed the filter to the unit. what could possibly be triggering the unit to go into delay mode without cooling the room to the set temperature.
It could be a number of things and depending on how the system is controlled and what controls are installed in the system will depend on the problem. A low refrigerant charge could make it go into delay mode after running for a time. That is usually tied to a low pressure switch in the system. Alternatively, a high pressure switch could also be causing the problem although most high pressure switches in HVAC systems are manual reset and not automatic reset. Low pressure switches are typically automatic reset. Something could be getting hot and shutting down, then when it cools it starts back up again. The best thing to do is to call the installer and ask them to send a technician to check it out. Most reputable companies (should be in writing in the contract upon purchase agreement) will cover most things under a warranty for one year. Besides, if installed by a reputable company, the unit should still be inside the manufacturer’s warranty period so there will be/should be minimal costs involved for you. The most common warranty for a new system is five years for parts but you have to pay for labor. Definitely call an HVAC service company because things like this tend to never get better. Only worse. Good Luck!!!
I just bought a honeywell wifi thermostat. I tried the Green wire delete as per honeywell, but cant get anything to work. Now mind you i blew the 3 amp fuse in the air handler. I also have a seperate baseboard hot water heating system. i can get that to work no problem. the wires on the air handler are as follows red on r, green on g, and blue on c. somehow I need to wire the red and white that turn on the compressor to this mess. I didn’t wire it originally. can someone please help me
take some photos and upload them on our photo upload page. I will look at it and try to help. I need the photos of the wiring at the thermostat and the air handler.
How to wire a delay timer to a compressor
It needs to go in the control circuit for the compressor. It’s easier to hook up a digital thermostat that has a delay built into it for the control of the compressor.
The central air conditioner/heater waits until it gets uncomfortably warm before the AC turns on, then stays on until it is to cold. In cold weather, the heater waits until it gets uncomfortably cold before the heat comes on, then stays on until it gets to hot. The wall thermostat has been replaced two times with new ones. Does that mean that the timers need to be replaced?
no, it sounds like a thermostat problem. Too much temp swing. There are many different thermostats that will help you solve this problem.