Condensing unit time delay bypass ?

[Bobe5531]

I had a unit today that customer complained that whole condensing unit would shut down for significant periods of time while the indoor fan motor kept running and turning the cooling system on / off at the stat had no effect. I was wondering if any of you guys had bypassed time delays that are enclosed in the condensing units ? I know the thermostat has a built in 5 minute delay.

Thanks,
Bob

[Bseliger]

Some people put them in the condensing unit because of previous or other problems. Short run times... etc. If there was one, im guessing it would be by the contactor. I ususally cut the control wire and splice the module in before the coil.

[Bobe5531]

Some people put them in the condensing unit because of previous or other problems. Short run times... etc. If there was one, im guessing it would be by the contactor. I ususally cut the control wire and splice the module in before the coil.

It is a little circuit board right near the contactor. I believe that it comes standard on some condensing units. I just wanted to know if anybody has had to bypass them because of issues with the CU running properly.

[Bseliger]

Ive never seen them come standard on CU, but most of my experience is on refrigeration and Ice makers. Mayber check with manufacture to see if it came installed, im guessing a tech put it on.

[Bobe5531]

No I think they are quite standard from some manufacturers. I run into them quite often in the Chicagoland area.

[Acexpresss]

If you have an older furnace i have seen where the fan control will pick up extreme attic temps and bring on the blower when no call was made by the t-stat. To remedy this you would adjust your fan control limits. I see that you are well north of me so im not sure if this would apply to your situation.

[Baycienda]

There are a lot of residential condensers that have a built in time delay. It could be a little 2"x2" square board or a 2"x2" black box. But the main thing is to inform the customer why there is a delay. It doesn't hurt to bypass the outside time delay if the thermostat has one. Make sure you find out if its short cycling because its oversized and inform the customer. And make sure it is running correctly. It could be over heating.

[pacnw]

your post is vague on the details!!

did you actually go to this customer's house?

if so, what is the problem?

is there actually a timer in the CU?

many stats do have a delay feature, but not ALL. even those that do can have them eliminated.

[Bobe5531]

your post is vague on the details!!

did you actually go to this customer's house?

if so, what is the problem?

is there actually a timer in the CU?

many stats do have a delay feature, but not ALL. even those that do can have them eliminated.

Yes I was at the house. The system was working fine while I was there ,the complaint was that the CU would completely shut down every now and then while the indoor fan continued to run while in cooling mode. Yes there is a timer in the CU and I bypassed it. I took amp , volt readings, pressure check and all looked fine. Checked for loose wires too. Hoping that bypassing the timer did the trick. Hard to troubleshoot something while its working fine. I have another service call tomorrow with the same complaint.

[MicahWes]

Do they have a load-shedding device installed by their electric utility that cuts the condensing unit for 15 or so minutes during peak demand times?

[IRBH]

Have seen those "Delay-on-break" timers go intermittant.
With a delay built into the stat, it's redundant anyway!

[goedelite]

I am not an HVAC tech; just a physicist with an HVAC in my little condo. So take what I say as an effort to help but don't bet your HVAC on it.

The condenser unit contains a compressor, compressor motor, and a condenser-coil blower-motor plus associated circuitry. The indoor fan blows the cool air (or heated air) through the living quarters. It is turned on by the thermostat and a fan relay.

The indoor fan may be on independently of the condenser system. If the compressor does not turn on and it is good, then it is not energized. Either the contactor is not closing the compressor-motor's circuit, or the internal protective circuitry of that motor has opened its circuit. That circuit would open if the motor were overheating from too heavy a load. A third cause of failure to run would be a bad run capacitor. The motor is an induction motor that requires a phase shift between the fields of the stator and rotor windings. That is the purpose of the run capacitor. The voltage across the capacitor is usually over 240V. They are dangerous to handle by an uninformed person even with the power off and the fuses pulled! The capacitor can be tested with an ohmeter, if one knows how. Otherwise, call a technician!

If the run capacitor is good, then the contactor which closes the compressor-motor circuit must be checked. The is also a higher echelon job. If the contactor is good, then the comp-motor is overloaded. This can happen if, for example, the condenser-coil were not being cooled by the blower-motor. If the compressor and compressor-motor are good, it is possible that the run capacitor (a second one) for the blower motor has failed. What I wrote before about caution applies. The blower-motor and the compressor-motor are separate circuits.

The delay-on-break timer prevents the compressor-motor from restarting immediately after it has been turned off. Were it immediately restarted, the compressor would be working against the high pressure fluid it had just delivered to the system. That would be starting against a heavy burden. The motor would draw excessive armature current for lack of back emf in a slow start. For that reason, a delay-on-break device is placed in the thermostat's circuit. It is not a good idea to defeat this protection or to alter the delay time from that recommended by the manufacturer of the compressor/motor system.

[Bobe5531]

I am not an HVAC tech; just a physicist with an HVAC in my little condo. So take what I say as an effort to help but don't bet your HVAC on it.

The condenser unit contains a compressor, compressor motor, and a condenser-coil blower-motor plus associated circuitry. The indoor fan blows the cool air (or heated air) through the living quarters. It is turned on by the thermostat and a fan relay.

The indoor fan may be on independently of the condenser system. If the compressor does not turn on and it is good, then it is not energized. Either the contactor is not closing the compressor-motor's circuit, or the internal protective circuitry of that motor has opened its circuit. That circuit would open if the motor were overheating from too heavy a load. A third cause of failure to run would be a bad run capacitor. The motor is an induction motor that requires a phase shift between the fields of the stator and rotor windings. That is the purpose of the run capacitor. The voltage across the capacitor is usually over 240V. They are dangerous to handle by an uninformed person even with the power off and the fuses pulled! The capacitor can be tested with an ohmeter, if one knows how. Otherwise, call a technician!

If the run capacitor is good, then the contactor which closes the compressor-motor circuit must be checked. The is also a higher echelon job. If the contactor is good, then the comp-motor is overloaded. This can happen if, for example, the condenser-coil were not being cooled by the blower-motor. If the compressor and compressor-motor are good, it is possible that the run capacitor (a second one) for the blower motor has failed. What I wrote before about caution applies. The blower-motor and the compressor-motor are separate circuits.

The delay-on-break timer prevents the compressor-motor from restarting immediately after it has been turned off. Were it immediately restarted, the compressor would be working against the high pressure fluid it had just delivered to the system. That would be starting against a heavy burden. The motor would draw excessive armature current for lack of back emf in a slow start. For that reason, a delay-on-break device is placed in the thermostat's circuit. It is not a good idea to defeat this protection or to alter the delay time from that recommended by the manufacturer of the compressor/motor system.

I have seen time delays go bad and the only way to get the system started is by bypassing it. Also majority of thermostats have built in time delay to protect the system

[Poodle Head Mikey]

Just off the top of my head it seems more likely to be a safety opening than it does a defective or redundant time delay relay.

Although . . . maybe a safety opening And a 10 minute combined time delay. <g>

What components are in the control circuit? Any anti freezing stat on the evap coil? Some units do come standard with an anti-freeze-stat. HP? LP? What can shut the condensing unit off besides the thermostat?

PHM
------

I had a unit today that customer complained that whole condensing unit would shut down for significant periods of time while the indoor fan motor kept running and turning the cooling system on / off at the stat had no effect. I was wondering if any of you guys had bypassed time delays that are enclosed in the condensing units ? I know the thermostat has a built in 5 minute delay.

Thanks,
Bob

[goedelite]

I have seen time delays go bad and the only way to get the system started is by bypassing it. Also majority of thermostats have built in time delay to protect the system

I suggest another way would be to replace it. Many sell very cheaply on the internet, just a few dollars. One that matches the old one would be a good idea.

There is no harm in doing without it briefly, but once the system has been running a couple of minutes and the high pressure is developed, then if the system for some reason power is interrupted (brief power-down, for example) and then resumed, the compressor-motor would be starting against a high back-pressure.

You may be right about thermostats with their own time delays built in, but since a compressor system is very expensive to replace, I would be cautious and insert a new, cheap time-delay to replace the old. But I am not an experienced tech, so I have to be extra cautious.

[Bobe5531]

I suggest another way would be to replace it. Many sell very cheaply on the internet, just a few dollars. One that matches the old one would be a good idea.

There is no harm in doing without it briefly, but once the system has been running a couple of minutes and the high pressure is developed, then if the system for some reason power is interrupted (brief power-down, for example) and then resumed, the compressor-motor would be starting against a high back-pressure.

You may be right about thermostats with their own time delays built in, but since a compressor system is very expensive to replace, I would be cautious and insert a new, cheap time-delay to replace the old. But I am not an experienced tech, so I have to be extra cautious.

I guess seeing as 95% of Condensing units dont have one of these I dont see any problem with bypassing them on units that do have them.

[Bobe5531]

Just off the top of my head it seems more likely to be a safety opening than it does a defective or redundant time delay relay.

Although . . . maybe a safety opening And a 10 minute combined time delay. <g>

What components are in the control circuit? Any anti freezing stat on the evap coil? Some units do come standard with an anti-freeze-stat. HP? LP? What can shut the condensing unit off besides the thermostat?

PHM
------

That might be possible, but as soon as I bypassed the timer the compressor and fan started up and ran prefectly, so I assumed the problem was the timer.

[goedelite]

I guess seeing as 95% of Condensing units dont have one of these I dont see any problem with bypassing them on units that do have them.

A one in twenty chance of being wrong is an acceptable statistic where the cost of being wrong is not high. You are right about that.

Another thought is the age of the system. Newer thermostats may have the time delay built in as you suggest. I live in an older condo. My AC system has the delay-on-break as an external part in the thermostat circuit. Also, I live in Florida where tropical storms and high winds through above ground power lines often cause power interruption. For these reasons, I have a battery back-up on my computer, and a delay-on-break on my AC.

I enjoyed the exchange with you. Best wishes!

[CoolWine]

I think what several are referring to as a "delay-on-break" is actually a "delay on make". Different animals. Different purposes.

[Poodle Head Mikey]

Can you detail the different purposes ?

What is each type intended to accomplish?

PHM
-------

I think what several are referring to as a "delay-on-break" is actually a "delay on make". Different animals. Different purposes.