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Jim Young
06-15-2007, 12:10 AM
Need help from AC experts. Our AC unit seems to be cycling alot now-a-days. The unit comes on for about 30 seconds and then shuts off again for another 30 seconds (or so). Then it starts over again. The whole time the furnace blower remains on. Sometimes it runs normal, blower on then compresser on for several minutes then both shut off. Is my compressor dying? Or is there something else going on?

Gary Herrmann
06-15-2007, 4:06 AM
Is it sized appropriately for your house? If the unit is too large (number of tons) it could well cycle a lot.

mark page
06-15-2007, 6:03 AM
I don't know much about home systems but if same principles as automobile units, it could be as simple as low on freon or have a restriction somewhere. Auto units have high and low pressure switches and will shut the system down if it detects either one. Low pressure is low on freon, high pressure is either overcharged or a restriction in the line, condensor, evaporator, etc.

Jeffrey Makiel
06-15-2007, 7:16 AM
Jim,
I'm no expert either, but...

1. Low on refrigerant: check the suction line (the fat copper line) coming out of your indoor coil (evaporator coil or "A" coil) to see if there's frost or icing on it. If it does, you may have a small leak and need servicing.

2. Restricted air flow inside your house: this will also cause your unit to short cycle also. Make sure the filter is clean and all register grills are open. Also, high allergin filters cause a lot of restriction. If they are clean and open, you still may have flow restriction due to a frozen indoor coil from a low charge. Then it's back to step one.

3. Other less likely things to check are:

a) Make sure the outside condenser coil is clean. Remove all debris and spray with a hose (with unit shut off). Let dry for about 1/2 hour before restart.

b) Make sure the big fan on the condenser is spinning when the compressor is running.

c) Make sure the indoor fan is on the correct speed. A/C usually requires the indoor fan be at a higher speed for cooling and a lower speed for heating (assuming you have a hot air heat and not just an air handler). Normally, your system does the fan's speed change automatically. A very general rule of thumb is to see about a 20 degree temperature drop across the indoor coil. 16 degrees can also be OK if it is very humid in your house when you start the system.

Good Luck...Jeff :)

Al Willits
06-15-2007, 9:38 AM
Look on the wiring diagram and see if there's a low pressure cut out, or look on the suction side of the system in the condending unit for it.
30 secs is to short for the comp cycling on the limit (normally) and if the furnace fan is staying on and thermostat fan control is in the "auto" posistion I'd suspect low freon.
Unit at rest pressures could be high enough to run unit, then when comp starts, the low side of the system (low pressure) would drop far enough to trigger the pressure switch.
Also dirty condensor would heat the comp hot enough it wouldn't cycle that often, takes much longer normally to cool down and reset.

Easy to check if you have, or can get a set of A/C gauges.

Good time to remind all to make sure their condensing units are clean and check their furnace filters.

Al

Randy Denby
06-15-2007, 9:49 AM
Well...I am considered an expert. And I must say, the non-experts are good.
One more possibility I can think of off hand, would be to check your contactor inside the condensor (outdoor unit). Ants have a bad habit of being drawn to the electrical field and getting in between the (points) contacts, which will hinder/stop current flow. And it wont do it every time its calling for cooling sometime.It can cause voltage drop and the unit will cycle on overload.Or stop current flow altogether. Just look for dead ant bodies in the cabinet/contactor.
Also, check the outdoor fan motor to see if the bearings are going bad. WIth the unit off, stick a small blad screw driver thru the grill and see if it spins easily or has any side to side play.
With the unit "short cycling" tho ,I tend toward the unit cycling on low pressure , which can be low on refrigerant or restriction of refrigerant flow or air flow.,as the most probable cause.

There can be many possiblities and might warrant a technician to have a look at it. Wouldnt hurt to have it serviced anyways . Good luck
Randy

Al Willits
06-17-2007, 4:36 PM
So...we ever find out what was wrong?
Inquiring minds want to know...:)

Al

Jim Young
06-17-2007, 6:12 PM
So...we ever find out what was wrong?
Inquiring minds want to know...:)

AlI will be calling a tech this week. I looked over the condensor unit and found no bugs or anything kinked. The top fan support looks a little rusty but other than that I see nothing wrong.

Jeffrey Makiel
06-17-2007, 7:33 PM
I think I may have jinxed myself. Now my unit needs refrigerant! Never talk about appliances in front of 'em! They listen.

I like to do my own repairs around the house, and I only need a little bit too. Unfortunately, one needs a license to buy R-22 these days. Phooeeey!

Oh well...Jeff :)

Al Willits
06-17-2007, 8:52 PM
To bad your so far away Jeff, I have a jug or two laying around.
Bit fer to stop by unfortunately.

Al

Pat Germain
06-18-2007, 2:08 PM
My dad had this exact problem with his home A/C system. I told him it shouldn't operate that way, but he disagreed. His thermostat was an early electronic model and I recommended he replace it.

My mom finally convinced my dad to replace the thermostat and it fixed the problem completely. Since it's under $50 for a decent thermostat, it would be worthy trying. This time of year, you'd be lucky to get an HVAC guy to answer the phone for $50. :)

Al Willits
06-18-2007, 3:29 PM
You could by pass the stat to check that, having a bad brain day, but I'd think jumpering r to y would do it, try at your risk though.

Al

Jeffrey Makiel
06-18-2007, 8:38 PM
Well...I broke down and called an HVAC company up today. I called four of them from the yellow pages until I got a real person. Turns out I needed 3 lbs of refrigerant which is more than I thought, however, I was not at home when he came.

The charge was $75 per pound of refrigerant. This price included the techs service charge too. I guess it's not that bad. But I could have bought a 30lb tank and new guages if I were allowed to.

-Jeff :)

Randy Denby
06-18-2007, 8:50 PM
75$ a lb ?:eek: :eek: I have got to go up on my pricing.....I charge 12.85/lb

Al Willits
06-18-2007, 9:00 PM
Jeff, how old is the unit?
Depending on time of leak down, 3.5#'s is a pretty good leak and if it took only a couple of years to drop down, the leak should be able to be found.

Make sure all the service port caps are tight, they usually have a O ring in them to seal and they leak a bit after time, there is a sealant that can be used on them also.
Also the schader valve has a rubber seal in it that can leak, this is replaceable with out dumping the charge with a valve stem tool.
Least your up and running.

Al

Jeffrey Makiel
06-19-2007, 6:54 AM
It's circa early 1960s. About 45 years old made by Fedders. It amazes me. It's like a very old Kelvinator refrigerator that everyones Grandma has in their basement to keep cream soda cold. It just keeps running.

I suspect it's the service valves too. I need to do what you recommended. Is it a special sealant for refrigerant systems? Or will teflon paste do?

I keep saying that I'm going to replace the unit when I do some alterations to my home. However, based on economics, a new unit has a 20+ year payback in energy savings assuming the new unit has a SEER of 13 and the old unit has a SEER of 6 or 7. I use it mainly at night when it's really warm and humid...and that's only 2 to 2 1/2 months a year. So, I'll probably keep the old boy runnin' until I get motivated to begin work on my home.

-Jeff :)

Randy Denby
06-19-2007, 9:30 AM
It's circa early 1960s. About 45 years old made by Fedders. It amazes me. It's like a very old Kelvinator refrigerator that everyones Grandma has in their basement to keep cream soda cold. It just keeps running.

I suspect it's the service valves too. I need to do what you recommended. Is it a special sealant for refrigerant systems? Or will teflon paste do?

I keep saying that I'm going to replace the unit when I do some alterations to my home. However, based on economics, a new unit has a 20+ year payback in energy savings assuming the new unit has a SEER of 13 and the old unit has a SEER of 6 or 7. I use it mainly at night when it's really warm and humid...and that's only 2 to 2 1/2 months a year. So, I'll probably keep the old boy runnin' until I get motivated to begin work on my home.

-Jeff :)

Jeff, unfortunately, most of these old gems are gone down here in texas. Season is at least 4 months sometimes 5 months and they run 24/7. I did find an old American Standard last summer that was put in in the early 60's. It still amazes me the quality they had back then. Everything was heavy duty. And for the most part, the motors and compressors were 900 rpm vs. 1075- 1750 rpm of today.They kept upping the rpm to gain efficiency at the expense, I feel, of longevity.
As to the service valves/caps...use some teflon tape instead of paste.
Randy

Al Willits
06-19-2007, 12:02 PM
""""""""""
I suspect it's the service valves too. I need to do what you recommended. Is it a special sealant for refrigerant systems? Or will teflon paste do?
"""""""""""

Ya, there's a special leak lock liquid that comes in a tube we use, telflon may work, but never tried it.
Can't find it let me know, maybe I have some laying around.

45 years old???? sounds like the Crosley refrig I had in my garage that was over thirty years old when I got it, and it worked for close to 15 years after that, I wouldn't spend any more than you have to on it if I was you. :)

Randy Denby
06-19-2007, 12:34 PM
I wouldn't recommend any teflon paste/leak loc on the shraeder valves. When attaching refrigerant hoses the paste will get in the hose ends and could possibly get into the system when charging....very slight chance but not worth gumming up the core,hose, drier ,metering device ,etc. Leak Loc blue paste can keep the core from seating if it makes its way into the core seat..Best bet is to buy new shraeder caps or replace the o-rings inside them. Actually, just tighten the schaeder caps and leak check them with thinned dishwashing liquid and see if bubbles .
I
The king valve cap is ok to put leak loc on.

Good luck