Replaced capacitor, A/C unit works but won't turn on?

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Old 08-12-11, 06:34 PM
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Question Replaced capacitor, A/C unit works but won't turn on?

Hello everyone!
I've been trying to figure out this issue all day.

My dad came over to help me out, as he knows quite a bit about HVAC, but he was ultimately stumped.

So, we have an older Rheem air conditioning unit, and earlier this year it was freezing up, but we charged the unit and it's been working well ever since-- at least until last night. I'm not sure if this is relevant, but it has been VERY HOT this year here, and the past few days have been the first days below 100 degrees Fahrenheit in a few months.

Last night, the blower was blowing just fine, but when I looked at the A/C unit, the fan and the compressor weren't turning on.
Today, my father and I took a look at the unit-- first he tried replacing the contactor-- it seems like once he did that, we started having the other issue, which I'll get to in a minute. He replaced the 20 amp contactor with a 30 amp, but he said that shouldn't be a problem.

It still didn't fix the issue, so we took a look at the capacitor-- and the top was all bubbled up, it seems that it went bad! So we went out to a local A/C supplier and picked up a new one. We replaced the capacitor without issue.

When we manually depress the contactor, the A/C unit now works fine-- the fan and the compressor kick on and work well. But the thermostat no longer seems to activate the contactor...

Just to be clear, we did switch the new contactor with the old one, and the issue persisted. My father checked out the charge difference (sorry, I'm not sure if that is the correct term) between the wires from the thermostat/ furnace, that tell the A/C to start working on, and instead of having a 24 volt difference, there is no difference (which he interpreted as the thermostat not telling the A/C unit that it needs to turn on, even though it should).

The thermostat still would make a small clicking sound (as it always has) when I turned on cooling, and had the thermostat lower than the ambient temperature-- but it did not turn the air conditioning on. Additionally, flipping the fan switch from "auto" to "on" no longer turns the blower on.

So, we went out and got a new thermostat (even though it didn't make sense that the thermostat would suddenly stop working completely in the space of a few hours), and hooked up the new one. (The old one was a White Rodger, the new one is a Honeywell).

It still doesn't work.

We looked at the wires as we switched the thermostats, and they look perfectly fine-- no burns, the wires are un-kinked and look to be in good repair.

It seems like we fixed what was initially broken, but now we have some other problem, and I have no idea what to try next!

We double checked the circuit breakers, and none of the circuits need to be reset.

Any thoughts? Thank you in advance for any help! I'll keep an eye on this thread, and update as requested!
 

Last edited by chloeishere; 08-12-11 at 08:13 PM.
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Old 08-12-11, 07:10 PM
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Press the reset button located outside of the condenser.


 
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Old 08-12-11, 08:13 PM
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Originally Posted by Houston204 View Post
Press the reset button located outside of the condenser.


Hi! Thanks for the suggestion. I looked all over the back of that thing for a reset button, and I could not find anything. It is a 10 seer Rheem air conditioner.

It is possible that there is one inside the case, but it's dark outside and not a great neighborhood, so I'm going to wait until daylight to take off the cover tomorrow and take another look to see if there's a reset button somewhere that I missed-- I'll let you know if I find one.

Would the A/C still work if you depressed the contactor, even if it needed to be reset, because it does still work? I did a bit of googling and some people said that only Rheem heat sinks have reset buttons.
 
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Old 08-12-11, 09:13 PM
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The reset can also be located at the pressure switch.
You can follow the 24VAC wire from the coil side of the contactor to the pressure switch.
 
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Old 08-12-11, 10:30 PM
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Manually engaging the contactor would still start the unit with a tripped pressure switch.

Pressure switches are not limited to heat pumps.

 
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Old 08-13-11, 10:26 AM
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Hi again, Houston!

Well, I opened it up and looked around. I'm not entirely sure which wire is the 24VAC, I know it's low voltage and alternating current, and I thought it was the one that comes from the thermostat? I've poked around in there for about 20 minutes, and I can't find any sort of button.

Here's the wiring diagram from the case (I've been trying to interpret where to look from this, but I'm not very good at interpreting wiring diagrams to real life):

I thought the HPC (High Pressure Cut-out Control) on the diagram was the wire I was looking for, so I looked for the brown wires, but didn't find anything that I could manipulate on it. It does say OPT above it, which means it's optional? Would that be inside or out of the case?

This is what the electronics inside the case look like:


And here's a side view that includes the compressor. It's really dusty in here, sorry. I've wiped off the wires since I took this picture so I can tell which wire is which color (we are going to wash off the coils as soon as we get the AC working again!):


Does that help anyone to figure out where I should look for the pressure reset button? I am trying my best to figure it out, but I am fail.

Thank you!
 
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Old 08-13-11, 10:47 AM
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The brown and yellow wires on the right side of the contactor are low voltage. They run to the top right of the picture. Trace these wires to the field installed low voltage wires which are commonly red and white. A pressure switch would be between these 2 points.

Wow, that is the dirtiest condenser that I have ever seen. Do you have a Chow or laundry mat?

Do you have a meter? If so, do you have 24VAC at the red and white field installed control wires? Do you have 24VAC at the yellow and brown wires at the contactor?

Your pictures are too close. I cannot see the liquid line. I only see the hot gas line and suction line. Take a step back and left shoot the compressor again. A shot of the outside area around the refrigerant lines might also show a pressure switch.
 
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Old 08-13-11, 12:00 PM
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Originally Posted by Houston204 View Post
The brown and yellow wires on the right side of the contactor are low voltage. They run to the top right of the picture. Trace these wires to the field installed low voltage wires which are commonly red and white. A pressure switch would be between these 2 points.

Wow, that is the dirtiest condenser that I have ever seen. Do you have a Chow or laundry mat?
Nope! The people who used to live here did almost nothing to maintain the house (and for all we know, everyone else before them-- maybe they had a chow!). The condenser probably hasn't been cleaned in at least 6 years. This is our first home, so we weren't aware that it should be cleaned annually. We do have a cat, but he doesn't shed much (or go outside!).

I don't have a meter, but my father does. The problem that he could detect was that the low voltage (the yellow and brown wires going to the contactor) had no current. We didn't check the field wires. He wasn't around when we installed the thermostat, so I'm not sure if we had the power line still working there or not-- we're probably going to take out the new thermostat since that isn't the problem, and maybe I will borrow his multimeter so we can doublecheck that.

Edited to Add: The furnace blower doesn't turn on anymore, if we switch on the thermostat, either. Does that point to a problem further down the line? It used to turn on yesterday, even when the AC initially wasn't working. No circuits are tripped, and the furnace switch is "on."

I went down from the yellow and brown wires, but there is no switch where they run into the other wires (which have red and blue stripes). (See this picture)


I run into the back wall of the house if I try to pull back further from the pictures, but this is what I came up with.
Larger view of A/C (you can see the lines here)

Where the wires go back into the house.




I swear we aren't dirty people, but the A/C unit doesn't make it look that way!

Thank you for your help!
 
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Old 08-13-11, 03:44 PM
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If your furnace is not an older Rheem or Rudd it may have a 3 or 5 amp blade type automotive fuse that has popped.

A Carrier example with a 3 amp fuse...


Rheem and Trane gas furnaces were decades behind everyone else and can require a new transformer if someone did not remove power to the furnace before replacing a stat or contactor.



Will the fan run if you remove the stat and jumper the R and G wires?


2 spade connectors and a 3 amp fuse can be added to protect the next transformer.



Do you have a float switch? (less likely)
 
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Old 08-13-11, 05:39 PM
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Rheem and Trane gas furnaces were decades behind everyone else and can require a new transformer if someone did not remove power to the furnace before replacing a stat or contactor.
Hi! It ended up being the 24 volt transformer! Luckily, RadioShack had one for sale, thank goodness, or we would have had to wait til Monday to buy one! I am positive we removed power from the AC unit before replacing the contactor, but I know we didn't remove power to the furnace. If we need to mess with it again, I'll be sure to remove power to the furnace, as well.

It'll take a while for the house to cool back down, but it's a relief to have A/C back again (my allergies are grateful).

Thank you for all the help, Houston!
 
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Old 08-13-11, 05:54 PM
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That is great news. I'm happy to have helped.
 
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