intermittent central air problem

[nine4gmc]

Hey guys, we just moved in to a home about 4-5 months ago and during the first week, started having problems with the AC. The previous owners had a NEST thermostat on the wall but replaced it with what looks like the older original thermostat that the house came with. It seemed like every few days, the AC would not automatically kick on, the temp would be low 80's in the house and you could set the thermostat to any temp, nothing would happen. I had a newer digital thermostat that I used in my old apartment and it worked fine so I swapped them out. Another week or so goes by and it's back to intermittent again. I try new batteries in the thermostat, no help, I try the old thermostat and it starts working again, but only a few days then it's back to same old stuff. I finally put the newer thermostat back up and for a month or so, it has worked fine but now it's low 80's again and burning up in here.

Apparently the thermostat is NOT the problem, since it does the same thing with both different type thermostats. What would you check first?

Thanks

 

[GMBracing]

sounds like a connection problem, check the wiring for tarnishing or bad connection

 

[nine4gmc]

Checked. It does it randomly with both thermostats but this time it's been 12 hrs since it last worked.

 

[LS6 Tommy]

Does the evaporator blower work properly with the stat in the "Fan Auto" setting? If so, check the contactor in the condensing unit. They get bugs/spider webs, etc. in them and they stick open sometimes.

Tommy

 

[kd3pc]

If you can get to the attic/crawl space/basement to see the actual wire, else time to break out the meter and check for continuity and voltage - correctly present....

check when "working" and then when not....

contactor check is in order as well, same with the plug "disconnect" at the outside unit, it may be corroded.

 

[joel63]

Does the evaporator blower work properly with the stat in the "Fan Auto" setting? If so, check the contactor in the condensing unit. They get bugs/spider webs, etc. in them and they stick open sometimes.

Tommy

^^^^^^^^
A good place to start.
I 've run across it in the past.
Ants like to play in the contacts in a contactor.

 

[Zrexxer]

Yeah I just had to replace the contactor in my condensing unit this past summer... *&^%$ fire ants got into it and shorted it out. My A/C guy put in a sealed contactor this time. The fire ants can go pound sand, now.

 

[nine4gmc]

The auto/on fan switch does nothing, it seems like last time this happened, the on fan switch may have worked but to be honest, I can't really remember for sure.

Since I can not get it to kick back on, I can not check while running, is there anything I can check while not running? It's a 4 wire thermostat with "G, Y, W, & Rc" connections.

Here is the thermostat

attic unit

and outside unit. the wire connectors on top look like the fan was replaced at some point

 

[nine4gmc]

Ok, I was checking continuity from the thermostat to the attic unit and everything was good, then I looked over and noticed the drip pan FULL of water. :tard:

Back working fine now, nothing to see here, move along

 

[nine4gmc]

Back Again! OK, the drip pan filled about 4 gallons over night, the home warranty people said that they would keep us on the books because it WILL fill up again and "that ______ line needs flushing". My girl spoke to them but missed hearing what goes in the blank up there.

Is this something that can be DIY repaired or will I need to have the service guy come out?

 

[kenfain]

Sounds like the drain line is clogged. Not letting the condensation drain. Use some compressed air to blow out the line, from the attic side. That'll likely solve that problem. Sorry I can't help with the other one.

 

[JackDiddly]

If you can get access to the underside of your evap coil (the side the air is blowing into) there is a good chance that the previous home owners were bad filter changers and the fins of your evaporator coil could be blocked which in turn will cause a properly charged unit to start freezing up and turning the coil into a block of ice because of improper airflow. If you clean it try not to bend the fins depending on how bad it is you might need a fin comb to scrape off the nastiness.

 

[BillK]

gmc,
Is there a float or sensor that keeps the unit from working if the drip pan gets full ? My unit uses a pump to pump the condensate up and out of the house and if something happens to the pump there is a float switch that keeps the system from running so it does not soak the floor. Our unit at my business has a drip pan and it the drain does get clogged up once a year or so. I just blow it out with my compressor. I actually do it from the end where it drains out of the building

 

[JackDiddly]

Might have spoke to soon and misunderstood... but yeah there should be a drain line going somewhere from the evaporator coil out if you can cut it open blow the line out and ensure that its not blocked at the drain pan coming out, dust and dirt will mix with your condensation as the system is running and build up scale in the drain line.

 

[JackDiddly]

If you want to eliminate the t stat to see if it will run you can jump Red and Yellow (verify that you have 24v first), if it comes on and doesn't with the t-stat, then its likely the stat. The auto/on function won't work unless the G wire is connected at the furnace (Typically R is 24v (brings 24v potential from a transformer in the furnace to the stat) - Y is cooling, G for fan, W for heat.) Can't make out the low volt connections at the furnace in your pic.

 

[nine4gmc]

Thanks guys, there is a drain line from the evaporator core that looks to go inside the wall of the bathroom below and there is no drain in the pan that is sitting below the evaporator. I can see the drops of water coming out of the evaporator and dripping into the pan, there is a panel that I will need to remove to check the coil inside and the drain pipe. Thank you guys for all your help, I will update this tomorrow after I get back up there.

 

[kenfain]

No reason why you couldn't clear the drain from the outside, in. Other than the mess. If you've got an electrician's snake, that'd likely work also. I can't imagine they'd put in a drip pan without a drain.

 

[nine4gmc]

I thought for sure the drip pan should have a drain pipe as well but it doesn't and the drain for the evaproator does not go outside, it goes into the wall of the bathroom below, I assume to the sink drain inside the wall. The water heater has a drip pan as well but it does run out through the brick wall on the patio. I'm thinking they ran the ac drain to the sink so the patio would not stay wet all the time.

Should I plumb the pan into the pipe that drains the evaporator, maybe tee off or what?

Here are some pics of the evaporator drain pipe and the pan. The drain pipe is on the left with the tape over the stub sticking up.

You can see where the water is dripping from the rust stain on the pipe from the condenser.

 

[JackDiddly]

That pan looks like it has a float switch on it, which is most likely what is cutting off the unit when the pan fills(your t-stat takes its power from batteries so if the float switch trips your stat will not show any different but that switch interrupts the 24 v signal not allowing the stat to function as a switch, which is all it is). This is a fairly common installation practice. I am thinking that I was right with my first reply and your Coil is likely dirty, or if the primary drain is plugged the pan will overflow, if not you may need someone to check the charge of the unit (which can also cause it to freeze). The pan without the drain is a safety NOT something you should rely on you need to stop the water from dripping out of the evap coil. If it freezes like I previously suggested the unit will continue to run until enough ice has melted to fill the pan and cut the float switch which most likely interrupts the R wire between furnace and stat. I have also seen a lot of older evap drain pans that were made of metal get old enough to rust all the way through in spots allowing for the condensate to escape.

 

[joel63]

No reason why you couldn't clear the drain from the outside, in. Other than the mess. If you've got an electrician's snake, that'd likely work also. I can't imagine they'd put in a drip pan without a drain.

Time for a Wet/Dry vacuum. You may also consider removing the panel and checking the evaporator drain pan.

Some install a secondary drain pan with a float switch because:

#1 Don't want to take the time to run a secondary condensate line to the exterior

#2 Figure this method is good enough; when unit stops cooling customer will call for service.

#3 ??????

 

[zmaxmotorsports]

Does the evaporator blower work properly with the stat in the "Fan Auto" setting? If so, check the contactor in the condensing unit. They get bugs/spider webs, etc. in them and they stick open sometimes.

Tommy

 

[LS6 Tommy]

From what I can see in the pics, you're getting water in your emergency pan because there is no p-trap on the condensate drain line...

Tommy

 

[nine4gmc]

The drain line was clogged, thanks to you guys I used the shop vac to **** out all the trash and clean up the coils. Everything came clean and it's been draining normal, the water I couldn't vacuum out of the drip pan is even drying out now. I will be monitoring the drain pipe and make sure this don't happen again. Thanks for you guys help!

 

[southalabama]

Once a year I use the shop vac on my drain line. It's an older system and it clogs and dumps water in the hall.

 

[ckaz613]

In his situation you would not use a p-trap. Horizontal coil that the forced air is blown from furnace through coil to supply duct. A p-trap is nessasry when the air is pulled not pushed thru coil. But, if his drain is connected to a house plumbing drain, then he would need to have a p-trap to keep sewer gases from getting picked up the ac drain and brought into house from system.