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01-26-2011, 10:40 AM #1
OT: Heat pump off after 5 mins with work to do?
Outdoor temp is 35 degrees. Heat pump is a Ruud 2.5 ton unit R22 w/aux heat strips, 16yrs old. Clean air filter, unit looks fine. Tstat set at 68 degrees and ambient room temp is 66 degrees.
What it's doing: When heat is called for by Tstat then the heat pump turns on and runs for a few minutes and then turns off before 68 is reached. Several minutes later the aux strips kick in and bring temp up to 68. From there heat strips seem to be the order of business until unit turns itself back off. Later when heat called for again by Tstat it will cycle on again with the heat pump only running for a few minutes before shutting back off. Heat pump USED to run nearly all the time in cold weather. What's up?
Any suggestions as to what my problem might be appreciated.
01-26-2011, 10:53 AM #2
First thing you need to do is see if your Tstat it kicking out it's call for heat. Usually hear the relay kicking in and out. If it is staying in, I would want to check the current draw for the compressor. Some do have a auto reset thermal switch which would kick out early.
Lets go from there..
01-26-2011, 10:59 AM #3
When the outdoor unit is running, the refrigerant lines shold both be noticably warm. The larger line should be warmer than the small line.
If you can catch it when the ODU first comes on, and see if the lines are warm and then get cooler as it runs a bit, that'd be an indication its lost the gas and is cutting off on low pressure, which seems the most likely problem.
If the reversing valve dies, it typically fails to the heat position, but even if it was stuck in the cool position the compressor wouldn't normally shut down.
About the only two things I can think of offhand that would cause it to shut down and then restart would be low pressure and the klixon within the compressor that'll shut it down on a high motor winding temperature. You could verify if it was the klixon by checking for power to the compressor after it shuts off. Compressor contactor would still be pulled in and there would be power to the terminals on the compressor, but nothing happening.
01-26-2011, 11:17 AM #4
This morning I swapped the Tstats to see if that made a change and it didn't. I believe the Tstat is continuing to call for it to run but something else is turning it off. Also the contactor is opening when the compressor turns off. If I push down on the main contactor again it will come back up and run no problem.
I didn't know the heat pump would shut down on low freon but it certainly makes sense? I know in the summer if the freon gets low it will freeze the A coil in the air handler.
I will try to check the lines for a temp change as suggested.
I have a nice gauge set and know how to use it. I have added freon to this system a few times over all these years with no problem. Usually only 1/2 to 1lb is all thats needed mid summer to bring it up to snuff. Now you've got me thinking the leak is worse!
01-26-2011, 11:26 AM #5
If you have gauges listen carefully, DO NOT use the cooling side ports for testing. You may actually need to switch to cool mode for testing, I cannot remember. Also, as I said, the very first thing I would do is just put a amp hoop over the motor lines and see what the compressor is doing. 9/10 times, if the compressor is pulling good current, it is not overheating, especially that fast. If current is high or creeping up, there might be an issue there.
There is a pressure sensor in the condenser for heat mode. I would just bypass that for a quick test. If the heat stays on, you probably know what you need to do.
I see a LOT of leaks develop right at the test ports. Check for that...
01-26-2011, 12:07 PM #6
Just measured amps at 11.8 right up to the second it shut off.
The RLA for this compressor is 13.5 so it appears to be good on that.
With that I'm thinking the condenser sensor is detecting low pressure?
01-26-2011, 12:22 PM #7
yep....you are on the right track
01-26-2011, 02:01 PM #8
After adding 7.25 oz of freon I have the system working properly again now with the exception of the low pressure schrader valve. It was oily when I removed it and it has a leak. Seems like I remember Robinair or similar selling a pressure swap tool for these cores?
01-26-2011, 02:06 PM #9
Now listen carefully, go get a 2 cent oring and put it in the cap that goes over that port and cinch it down tight... That will usually seal your problem right there. many people forget to remove the cores when they solder and it cooks them.
01-26-2011, 02:21 PM #10
A friends mom has what I think is a Ruud heat pump.
It has a strip of frost what looks like two inches thick (that's on the outside of the housing, so it's hard telling how thick it actually is from the coil surface on out) and about a foot tall all around the outside of the unit.
I called my friend and told him I thought something was wrong with his moms system. He told me that they've called someone to check it and they weren't alarmed by what they saw. It has been doing it for a long time- like years. I noticed it last year.
Evidently there is nothing wrong as far as keeping the house warm, so I am puzzled about what is going on with that thing.
It bothers me, driving by and seeing this unit that looks like they are building an igloo. If I could get away with it, I'd get her garden hose and hook it up and hose that thing down til I melted the ice off it.
I sure wonder how those things work that it could be OK in the house and froze solid looking on the outside?
Would those heat strips you're talking about be keeping her warm all by themselves.
01-26-2011, 02:38 PM #11
Will do Viper, I appreciate your help.
On the Ruud freezing up. Maybe the defrost cycle just not getting it done?
01-26-2011, 04:20 PM #12
As JL said, it sounds like its failing to go into defrost. Most of them have a board in the control section of the ODU that controls the defrost cycle. There's usually a jumper on the board that sets the time between defrost cycles. Usually selectable for something like every 30, 60, or 90 minutes. When someone looks at the unit and doesn't see anything wrong with half the coil frozen, its time to get another, hopefully more knowledgable, set of eyes to look at it. Failure of the defrost board is one of the more common problems with a heat pump, and there's a half dozen different ways they can fail. You typically determine it ain't working and put in a new one without worrying how the old one failed.
When the outdoor temp is in the 40 degree range, the coefficient of performance of a heat pump will be in the 3 range. That means you get 3 watts of heat for every watt of electricity it uses. The electric strip heaters have a coefficient of performance of approximately 1. IOW, you buy a watt of electricity to get a watt of heat. A blocked condenser can easily double the power bill compared to what it would be with a properly functioning outdoor unit. You get more energy out than you put in even at 20 degrees outside temp. Starts to fall off pretty quick past that, and is down in the 1 to 1 range by the time the temp falls to 10* or so. The energy savings would pay for the repair in short order.
01-26-2011, 05:42 PM #13
They do sell a tool for changing the schrader core without removing the pressure but I don't know the name and it would be costly for just one use.
01-26-2011, 06:17 PM #14
I'm for the O-ring fix. Done it many times, then making a mental note to get back to it when it's Spring. Of course, I never do, but it's the thought that counts.
By the by......if you go that route, and follow my process of procrastination, I would strongly suggest a brass Schrader cap as opposed to those plastic ones that will invariably crack, thereby defeating the O-ring fix.
01-26-2011, 06:42 PM #15
Atty. Great to see you back. That is a good point on the brass caps. I guess I have not seen the plastic ones on a decent condenser but that does not mean they are not out there. Certainly are all over the automotive industry. I had a friend come by when I set one up last year and he sniffed it and found the leak at the port. I then put on my "special" cap and ne sniffed it again and got all excited... i was like "uh, so you don't know what an oring kit is?" No procrastination here, I have no plans to remove them....lol
01-26-2011, 07:17 PM #16
JL, you can pump the unit down and change the schraeder valve in most cases without losing more than an ounce or so of gas. This is assuming the leak is on one of the main service valves at the pipe entrance to the unit.
To pump the unit down means you close the liquid line valve, pull all the gas in the system back into the condensing unit, condense the majority of it to liquid in the condenser, and then close the suction line valve. At this point, you'd have only gas in the lines and the evaporator, at a pressure of just a few psi. With the service valves closed, the schrader valves are still open to the lines, but not to the condensing unit. You can then change out the valve core in a few seconds and the quantity of refrigerant that bleeds out during the change is minimal. The unit needs to be in the cooling cycle for pumpdown, and its ideal to do it on a cool, but not necessarily cold day.
The unit needs to be running. Close the liquid line valve (small one). You'll hear the sound of the unit change as the compressor pulls everything out of the system. Once the low side pressure drops sufficiently, the low pressure switch will cut the unit off. Quickly close the suction line valve and cut off the power to the unit at the disconnect. If you've got a gauge hooked to the service port on the suction side, you can manually engage the compressor contactor to pull the system pressure even lower prior to closing the valve, but always stop when you still have positive pressure. If you pull into a vacuum, you'll pull air into the system when you remove the valve core.
Now you're ready to change out the valve core.
When that's done, open the liquid line first to allow the system pressure to equalize. Then turn the unit power back on, and if the stat is still calling, the unit should restart.
In the meantime, pick up a hex brass cap for 1/4" OD flare fitting at the local refrigeration supply house and use it to cap the port with the leaking valve core. The knurled plastic or brass caps with o-rings are designed to keep dirt and water out of the service ports and they won't stop a gas leak completely. The hex flare cap will stop it. Last time I checked, a 30# drum of R-22 was going for about $185, so you don't want any of it getting away unnecessarily. Re checking for other potential leaks on the unit, quickest way to spot them is by the presence of an oily film in one area. The ref supply house will also have a small bottle of leak detecting soap bubbles that'll allow you to pinpoint leaks. Pretty cheap. A spray bottle filled with household ammonia will also work well to spot real small leaks. For some reason, a freon leak that soap bubbles won't hardly show up will make ammonia fizz like crazy. Another cheap diagnostic tool
And the thing to always check first when looking for a leak is to make sure all the schrader valve cores are tight. Next likely suspect is the refrigerant line connections to the outdoor and indoor units if they're flare or compression connections rather than hard soldered connections.
01-27-2011, 05:51 AM #17
Good stuff! Thanks so much guys!. I'm going to get some of those brass hex caps!
01-27-2011, 04:10 PM #18
They do make a valve core tool for swapping out core without loosing r22, If I remember it was not too much $. R22 UNITS ARE NOT BEING MADE ANYMORE, so R22 is getting more $'s. It's just a little hand tool with some o rings to hold in pressure, while swapping stem. Look online at some HVAC supply houses or find a AC guy to borrow one. Try Robinaire I think they have one on there site, but other supply houses are less $'s.