Is it normal that HVAC compressor starts 40-50 minutes after the outdoor unit turns on?

[Sandy T]

Hi experts,

After replacing the capacitor last year, cleaning the condenser coil and replacing the filters last week, and adding 1.5 lb refrigerant and sealant today costing $400 by a technician, I decided to ask for help here. The problem is that the compressor outside start sometimes 40-50 minutes after the unit turns on. It happens during the hot time of a day (like at 2-3pm). It doesn't happen during nights.

The technician said that it was because the refrigerant level was low, so he added refrigerant and sealant. One and a half hour after he left, it happened again. Please help me. The late start (40-50 minutes) of compressor is normal? If not, what else could be the reason? Compressor itself or some electrical?

Thank you,
Sandy

 

[Fitter30]

If the condenser fan is running and the compressor doesn't start its possible that it's off on a thermal overload. The overload is self resetting than it starts. A start kit might help the problem.
https://www.amazon.com/SPP6-Capacit...kit+for+air+conditioner&qid=1595513869&sr=8-4

 

[Sponsor]

 

[Sandy T]

Hi Fitter 30,

I greatly appreciate your help and advice! Yes, the fan is running but the compressor doesn't start for that long.
Then, my follow up questions are,,, I replaced the capacitor last summer. But, you mean the capacitor isn't enough to do the job?

And, do you have a clue what causes this issue? What makes the thermal overload off? To explain my situation better, my condenser is under a tree so it never gets a sunlight directly. I timed the length of AC's operation yesterday and today and noticed that it's operating just for 7-8 minutes once it's turned on in the morning or evening when it's not hot. In this case, there is no delayed start of the compressor. When it's hot (early afternoon), the AC ran longer than 10 minutes but once it's turned off, about 5 minutes later it started again (of course, in this case the compressor didn't start for 30 minutes). I googled this situation and learned it's called short cycling. But, isn't it natural to be automatically off when it's not hot and the thermostat meets the set temperature quickly? Greatly appreciate it if you share your knowledge.

 

[HudsonDIY]

A bad TXV will cause short cycling. I had one go bad on my unit last winter and it would not heat although the A/C worked fine but it can cause issues either way.

Also if you have a drip pan with a cutoff float switch it can do the same thing if the pan fills. Check the drain and make sure it flows freely. This is something we have to do in Florida on a regular basis due to the high humidity. I have a PVC fitting which will accept a garden hose. I remove the drain at the pan, connect the fitting and flush out the drain with a garden hose.

 

[Sandy T]

Hi HudsonDIY,

Thanks for the information about TXV. I did some research of it, and it seems my issue has something to do with TXV. Though I don't think I have a DIY skill for that job. Could you tell me how much you spent if you hired a tech for replacing it?

 

[HudsonDIY]

Sandy this is a time when it was good to have friends in the trades. I have a friend who works in commercial refrigeration that replaced it for me for the cost of the part and a six pack.

He did tell me he thought it would be about a $300-$400 repair including parts.

Probably best to have an expert take a look to be sure. I am far from an expert.

 

[Sandy T]

Thank you ! and good for you to have a friend with knowledge and skills !!

 

[LLigetfa]

When the compressor shuts off it can take five minutes or longer for the differential pressure to drop. Starting the compressor against high pressure can cause the motor to overload. Some units would have a timer to delay the restart.
https://highperformancehvac.com/delay-timers-air-conditioner-condenser-hvac-control/

 

[Fitter30]

Watch the condenser fan motor might be stopping or slowing down.

 

[Sandy T]

Hi LLigetfa,

Thanks for reference. I've read the article and have a question. Then, do you mean 40 minutes late start of the compressor is normal and even preferable? In the hot afternoon, the inside temperature keeps going up and it's not cooling for 40 minutes until the compressor runs. I'm not sure if this is really normal.

Fitter30, what do you mean? You mean the condenser fan motor will stop or slow down if I don't change the capacitor? Or the motor will eventually stop because of the late start of the compressor?

Thank you!!!

 

[LLigetfa]

My guess is that 40 minutes is after one or more thermal trips so then no, not normal and not preferable.

 

[Sandy T]

Hi LLigetfa, then, what do you think is the reason for the delayed start of the compressor? So far, the suggestions are adding a hard start kit or replacing TXV.

Hi Fitter30, I have read the reviews of hard start kit you suggested. It seems like it could solve the issue. But before trying it, my question is, if my issue is due to the shortage of electricity when the AC turns on, the compressor should start late every time when the AC turns on. Yet, this is not the case. The compressor starts on time (like 5-7 minutes late) in the morning. The very late start (40 minutes or so) only happens in the afternoon when the temperature is very high. So, I am confused and think that it should be related to outside temperature in a way or another. What do you think?

Hi HudsonDIY, do you think the TXV's operation is related to outside weather?

 

[LLigetfa]

My guess is that it is trying to restart too soon after stopping and the high pressure is throwing the motor into thermal overload. By the time the motor cools and the thermal overload resets, the pressure has dropped enough for it to start. I'm guessing the motor is dying.

 

[LLigetfa]

I used to work in IT and air conditioners were a royal PITA if/when there were power failures. The time it took for the backup generator to restore power was too fast and resulted in the A/C sometimes trying to hard start which was tripping the breaker. We had one unit that had a digital control which had a hard start delay option, but on power failure, it would revert to factory default with no hard start delay. Stupid design. I had an environmental monitor system that would page me when the server room got too hot but by then it was a race to drive the distance before other kit started shutting down from the heat.

I had another A/C in another sever room that would stop for some unknown reason. I had to tie ribbons on the louvers so that the security guards could watch it on camera and go restart it if it stopped. I also had it trigger an audio alarm at security.

 

[Bannerman]

A TXV is located in the indoor unit as it will vary the amount of high pressure liquid refrigerant that will enter the evaporator coil based upon the temperature of the suction line which returns to the outside condenser unit. Not all AC units utilize a TXV as many are equipped with a simple fixed orifice (aka piston). Unlike a fixed orifice which has no moving parts, a TXV does utilize moving parts and is therefore more prone to problems and more expensive to replace.

If a TXV is stuck in the closed position or if a TXV or piston is blocked with debris from within the refrigerant, it may take longer for liquid refrigerant to pass through and for the system pressure to equalize. If the amount of refrigerant passing through either device is restricted, then cooling will not occur or will be less effective than usual. As your unit does eventually run, is cooling performance as good as it has been in the past?

If the TXV or piston is not causing an issue, perhaps adding start kit may provide the additional start power needed if the compressor is attempting to restart before the system pressure has equalized fully.

 

[Sandy T]

Hi LLigetfa and Bannerman,

I greatly appreciate your explanations and suggestions. Speaking of cooling performance, yes it is as good as in the past and as long as the compressor runs, it feels very cool inside the house.

My bottom line question is why the delayed start of compressor only occurs in the afternoon. I'm not sure how a hard start kit, blow motor, or TXV is related to weather. Would anyone be able to enlighten me on this puzzling issue?

Thank you again!

 

[LLigetfa]

My bottom line question is why the delayed start of compressor only occurs in the afternoon.

Is it hotter in the afternoon and/or is the compressor unit in direct sun in the afternoon? Perhaps the building has larger windows letting in sunlight in the afternoon? When it is hotter inside, the A/C starts more often so the off-time between when it turns off and then back on might be too short and the pressure too high. This may be tripping the thermal overload on the motor. The higher ambient heat around the motor could also contribute to the thermal overload tripping.

Place a clamp-on meter on the compressor feed to monitor the current as well as a voltmeter to confirm the presence of voltage. If when you see voltage, you observe a short high current spike followed by no current it would indicate thermal overload.

 

[Sandy T]

Hi LLigetfa, yes, it is much hotter in the afternoon (above 90F) compared to the morning (75-85F), but the compressor is not in direct sun and my house doesn't have larger windows letting in sunlight. But, also yes the AC's off-time is just about 5-7 minutes between operations. If this short cycling or some higher ambient heat around the motor contributes to tripping the thermal overload, what is the solution? Do you still suggest replacing the motor or adding a hard start kit as someone suggest above? I also wonder why this is happening this year if the reason is the higher heat either inside or outside or both, which would be the same for this year and last year.

 

[Sandy T]

I had another technician taking a look at the problem yesterday and while doing so, I learned that I already had a hard start kit. Also, a worsened symptom was that the compressor didn't even start for two hours in the afternoon while the fan was running. So, I watered it to cool the compressor down and then it ran. I learned from youtube that a technician solved a very similar problem by closing the thermal overload.

The question is, just closing it or replacing it? Please experts,,, help me out.