One or two years ago my ac compressor was not working. I did some research and found the capacitor is often the problem. I tested it and the numbers were a little low so I swapped it at about 10 years old.

I started my system early this year and everything worked fine (as it did last summer after the swap). Just yesterday it was doing the same thing. I would turn down the temp and there was no click at the thermostat or the compressor - which is what usually happens before it kicks on.

I left it set to "cool" for a few hours and the system never came on so I turned it off.

Tonight when I got home I figured I would give it a shot and sure enough it kicked right on an cooled down the house 4 degrees in 10 minutes.

I don't want to get stuck when it gets really hot so I'm trying to be proactive.

Any thoughts on what this may be? Could it be the contractor? Is it possible the capacitor when bad again after such a short period of time?

Any advice would be greatly appreciated.

It's a Carrier system about 12 years old now. I can take it apart this weekend when I have time to do further inspection.

Thanks!

 

Not thinking that cap is bad after 2years.

 

Me either. As we speak it is running fine and kicked back on.

What could cause it to do this?

Years ago I had an issue where one of the low voltage connections had rusted out. I replaced with a water resistant wire nut so I don't think that is the issue.

 

If the compressor unit should be running and it isn't..... you need to check for 24vac on the two wires that go from air handler to compressor unit. If you have that voltage then my guess would be low pressure cut off due to low refrigerant charge.

 

You mentioned that when it didn't come on recently, you didn't hear a "click" from the thermostat. The click is the relay closing in the thermostat. If you're not hearing the click when you set the thermostat for cooling, the problem may be in the thermostat. If you can access the wires where they connect to the thermostat, when the A/C doesn't come on, try connecting the R, G, and Y terminals together. If the A/C comes on, it would point to a defective thermostat. Have you tried replacing the batteries in the thermostat?

 

Thanks - I will test those this weekend.

However since it was running all last night I suspect they will have voltage.

Do you know what the click at the thermostat is controlled by? The one time it didn't work I didn't not get the click there. I wonder if it could be something with the thermostat?

 

The click at the thermostat is a relay engaging.

 

Bob / PJ - Thanks.

I ran the AC all weekend without issue. Tonight it stopped working again so I took a look at the thermostat.

It does not have batteries (must be run off the 12v wire) but I connected the R/G/Y wires together and the compressor kicked right on.

So since it has no batteries to change, is it that the thermostat is defective or could this be a symptom of another problem? My guess is that the relay (which kicks on a second before the compressor) is either not getting a signal or is faulty.

The model I have is a Thermidistat which, according to the installation company, will control not only temperature but humidity as well. I did a search for the number on the circuit board and found it to be this discontinued model:

TSTATCCPRH01 - Programmable Thermidistat Control Description

They have a few for sale on eBay and other sites for ~$400 (yikes!), but I'm hoping I can replace with a current model (if necessary).

I have an older Honeywell thermostat for my oil / hot water system right next to it. I asked the installation company if they could wire it to that but they they said it was not compatible.

One other piece of information I should note is that this model has an outdoor temp sensor (so I was told). Both times it did not work it was cool outside (50's). Could that factor into why it was not working?

Here are pics of the model number and the wire connections:




I really wanted to get a new WiFi thermostat so I can control when I am not home. Is there a model that can handle the Carrier AC as well as the hot water system? I saw a Honeywell at HD that got good ratings, but would like something colorful as well.

But first things first, I would like to figure out this issue (and I wonder if last year's issue was not the capacitor after all?).

Thanks again for your assistance!

 

If the thermostat calls for A/C and you don't hear that click then it sounds like a thermostat problem. If you had a meter you could verify it.

You can also combine your A/C and heating systems together.

 

Pj, I do have a multimeter. Should I test the wires coming from the air handler as you noted in your above post or something else?

Also, I feel like I should only test when it's not working, correct?

 

It's been working fine so far this week. Any advice on what exactly to test?

 

Same model Carrier AC, roughly the same age. If I mess around with the time/day settings I can usually get it to come on. I think the thermidistat is bad but my AC guy insists it's the compressor and wants me to pay $850 installed for a new one. What did you ever find was the root problem with yours?

 

Henry,

The ac kept on working so I didn't do anything more. Try the suggestion above about the wires - if that works, perhaps get a cheap replacment and run that for a while. You will lose the thermidistat function though.

It would also be a good idea to replace the capacitor. I got mine online from west side wholesale for pretty cheap. They do go bad after a while so good preventative maintenance.

Finally, check the wires in the compressor and make sure your connections are good.

 

If you have a Carrier A/C unit and are experiencing intermittent issues, here's a possibility. I have a Bryant (made by Carrier) A/C unit that's currently ~25 years old. A few years after it was installed, it would intermittently not turn on. The thermostat would call for cooling, but the outside unit wouldn't turn on. Sometimes it did, other times it didn't. I took the cover off the outside unit (compressor/condenser) and looked at the wiring diagram. That model used a "time delay relay" for lack of a better term. It's purpose was to prevent the compressor from turning on too soon after it turned off. I spoke to the dealer who installed the unit and I was told that that part was a frequent failure item and wasn't really needed if you had a modern digital thermostat, since the thermostat has a 5 minute delay built in (A/C won't turn off until 5 min have passed since it was last running). I bypassed the "relay" and the unit has been working fine ever since.

I don't know if your unit has this time delay circuitry in it or not, you would have to look at the wiring diagram on the unit. If it does, that may possibly be the problem.

 

Bob,

I must have jinxed myself because it started acting up again tonight after no issues since I posted originally.

Can you go into more detail about the bypass? I would prefer to keep it OEM - is there a relay I can replace? How can I tell from the wiring diagram?

Thanks

 

I just connected the wires together behind the thermostat and it kicked on. I suppose it is an intermittent problem with the thermostat?

 

I also noticed that the temp outside was in the 50's again like last year. The thermostat clicks to call for cooling but the compressor will only kick on if I connect the three wires together.

 

If the outside temperature is in the 50's, you don't want to run the A/C, as you run the risk of it freezing up due to the low ambient temperature. Assuming you have a wiring diagram inside one of the covers on the outside unit, take a picture of the wiring diagram (make it as large as possible), and post a link to the picture. We can then tell you if you have a time delay circuit (not all units have them).

If the A/C won't turn on via the thermostat, but does if you connect the wires together, it points to the thermostat as being the problem. It's possible you have an intermittent relay in the thermostat. You can pickup an inexpensive thermostat to see if that solves the problem. If it does, then you can look into either getting your current thermostat repaired (unlikely) or purchasing a new thermostat with comparable features (likely to be pricey).

 

Bob,

Thanks. What is the safe cut off temp to run the compressor? Normally I would open the windows but my gf suffers from allergies.

Since this model has an outdoor temp sensor, is it possible that the thermostat is preventing the compressor from running? It does all the normal steps when it calls for cooling (clicks, flashes cool, the. Puts a small blinking triangle next to the cool button which would normally turn solid once the compressor kicks on).

I have my heating thermostat next to it so I can try and hook that up. I'll also try to snap a pic of the diagram tonight if the rain stops for a minute.

 

I'll be honest, I don't know what a safe temperature would be below which you shouldn't run the A/C, but I would expect it would be somewhere around 70F. Heat pumps are meant to be run in cold weather and have sensors that monitor freezing, as do some A/C units meant to be run in cool environments. I don't know anything about your thermostat, so I don't know if it senses the outdoor temperature and is preventing the compressor from turning on, but I suppose it's possible (if it knows what the outdoor temperature is).

 

I'd be leery of running my A/C when it is less than 55 if it is getting sun... 60 if it isn't.

 

Noted. I figured as long as it was above freezing I would be ok.

Rain didn't let up and the temp is still cool. I will post the wiring diagram but it may be a few days.

Thanks for your help!

 

Here is the wiring diagram.



The AC worked during the day but stopped working when the temp got below 55 (I had it on and the temp dropped).

I'm really starting to wonder if the outdoor tempurature sensor prevents it from turning on below a certain temp?

 

On the wiring diagram it refers to notes. What does note 14 say ?

The wiring diagram shows a blue wire bypassing all the safeties and it has a "refer to note 14".

I see what looks like a low limit switch (LLS) but it's connected across Y and C. That makes little sense.

In the sensor chain I see high pressure sensor, low pressure sensor and D? temperature sensor.

 

PJ,

14 says "Wire not present HPS, LPS, DTS or CTD are used".

 

From the wiring diagram, it appears that you do have a time delay circuit. It's labeled "CTD" and is in series with the sensors (low/high pressure and temperature). However, from your description that it appears to not start when it's cold outside, my guess is that the temperature sensor is preventing it from turning on rather than the time delay circuit. If you can follow the wiring and find the sensors (pressure & temperature), on a cold day when the compressor won't run, set the thermostat to call for cooling and check with an AC voltmeter to see where the 24VAC drops out. It appears from the wiring diagram that the 24VAC passes through the high pressure sensor, then the low pressure sensor, then the temperature sensor, and finally the time delay circuit.

 

Thanks. It seems to be working normally during the day when the temp is higher.

I'll try testing to see if it is the temp sensor causing the issue. I'm also going to call carrier to see what they have to say.