The house was a warm so I set the thermostat a couple of degrees lower. A short while later I noticed that no air was coming from the air vents and the outside compressor unit wasn’t running. The problem was caused by a broken condensation pump which triggered the overflow safety switch to shutoff the AC and prevent flooding.
Purpose of an Air Conditioner Condensation Pump
An air conditioner condensate pump is used when a drain line to the outdoors or a floor drain isn’t feasible, for example when the air handler is located in the basement. My home has two air handlers: one in the attic with gravity condensate drain line to the outdoors and another in the basement with a condensate pump.
The pump reservoir collects the condensate water from the air conditioner evaporator coil drain line in the summer and excess water from the whole house humidifier mounted to the air handler in the winter. A float switch activates the condensate pump when the reservoir is full to pump out the water to drain or overhead sewer line. If the water level rises to the high water mark, the float switch activates a safety cutoff switch to turn off the air conditioner to prevent flooding.
The condensate pump drain line is connected a brass tee fitting on top of the overhead sewer line:
How to Replace a Broken Air Conditioner Condensate Pump
I performed a couple of quick diagnostic checks on the central AC system:
- The thermostat relay was making an audible “click” when the temperature setting is lowered and the electronic display said the system was ON. This is good.
- The main circuit breakers for the inside air handler and outdoor condenser were not tripped, so the power wasn’t the problem.
- Taking a look at the condensate removal pump on the basement floor next to the air handler, I noticed it was full of water. The safety cutoff float switch had tripped due to the high water level to turn off the A/C system to prevent flooding.
“Oh great!” I thought to myself. It’s Sunday night and the hardware stores are all closed. There’s no chance of getting a replacement condensate pump tonight. I could call an A/C repairman for an after-hours visit – but there was another less expensive solution…
Temporary Fix for Broken Condensate Pump
As a temporary fix for the broken pump so I wouldn’t be sweating all night:
- I unplugged the condensate pump.
- Removed the four corner screws to the cover of the pump.
- Removed the cover with the pump motor and mechanism off the water reservoir.
- Carried the water reservoir outside and dumped the water.
- Reassembled the pump.
- Plugged in the pump power cord.
The float switch reset itself now that the pump reservoir was empty allowing the A/C system to operate. The air conditioner will run for several hours until the reservoir was full again. With the cooler outside temperature that night, the A/C reservoir was only 1/2 full the next morning.
Replacement Condensate Pump
My pump is a Little Giant Pump Company model VCL-24ULS with a 1/18 HP motor, 1 gallon water tank and will lift 150 gallons of water per hour to 16 feet high. The big box home improvement stores don’t carry this model, so I bought a replacement unit from Amazon.com:
The new condensation pump, installation instructions and sticker with a notice to clean the pump when changing the AC/Heater filters.
Install the New Condensate Pump
The new pump was simple to install and the job took no more than 10 minutes. The wiring diagram is in Operating and Maintenance manual.
The new and old pumps are shown in the following photo. The old pump died after almost 9 years, probably due to lack of maintenance and cleaning:
Remove the Old Condensate Pump
My pump has two input lines:
- Rigid white 3/4 inch PVC drain pipe from the A/C unit
- 3/8 inch inside diameter (I.D.) clear polyethylene tube from the humidifier (used in the winter with heating)
and one discharge line:
- a clear 3/8 in I.D. flexible polyethylene discharge tube that connects to a brass Tee fitting the overhead sewer line
Steps to remove the old pump:
- Turn off the AC at the thermostat.
- Disconnect the power cord to the pump.
- Remove the wire nuts that connect the AC/heater safety shutoff wires to the float switch. This is a low voltage circuit – typically between 12 and 24 volts.
- Remove the flexible 3/8 inch discharge tube from the barbed nipple.
- Remove the four cover screws at the corners of the pump.
- Lift up the pump cover and slide the water reservoir away from the the PVC drain pipe.
I needed to remove the cover because the rigid 3/4 inch PVC drain pipe extended an inch or two below the cover and I needed to tilt the reservoir to clear the pipe.
- Clean the drain pipe and lines with bleach and water.
- Set the new pump in place.
- Reconnect the drain and discharge lines.
- Reconnect the safety shutoff switch wires.
- Reconnect the power to the pump.
- Turn on the AC at the thermostat.
- Fill the pump basin with water and test.
Remove the cover screws and lift off the pump:
Yuck! Everything is covered in crud. It’s remarkable the pump lasted almost 9 years. I see why the new pump includes a sticker reminding you to clean the pump and basin when changing the air filters:
I removed the cover of the new pump because the instructions indicated there might be packing material inside. I found none.
The pump has two float switches:
- Pump motor On/Off switch.
This float rises and falls with the water level in the basin. When the high water mark is reached, it triggers the pump On switch to pump out the condensate water.
- High-water safety cutoff switch.
The Normally Closed switch is connected to one side of the thermostat low voltage circuit that calls for cooling. When the switch is triggered, it opens breaking the circuit (shuts off the low voltage signal) causing the air conditioning unit to turn Off.
The new pump was simple to install:
- Reattach the two wires from the air handler to the two pump wires with wire nuts.
The order of the wires doesn’t matter because it’s simple switch inside the pump.
- Insert the drain lines and reattach the discharge line to the barbed nipple.
I filled the reservoir with water through the hole at the front-right corner to check the pump operation. It worked fine.
Diversitech CP-22 Condensate Pump
The CP-22 pump with a new 3/4 inch PVC condensate drain pipe and 1/2 in O.D. x 3/8 in. I.D. polyethylene discharge tubing:
The Diversitech CP-22 pump is wired the same as the Little Giant VCL-24ULS so it’s a drop-in replacement:
Little Giant vs Diversitech Pumps
Which pump is better – Diversitech or Little Giant? Both pumps are rated for about 22 feet of head (vertical lift). At zero head the performance and warranty are:
- Diversitech CP-22 @ 96 gal/hr.
- 24 month warranty
- Little Giant VCL-24ULS @ 270 gal/hr.
- 12 month warranty
The Little Giant pump is more expensive but also more powerful with about 2.8 times more flow capacity compared to the Diversitech pump. I have about 15 feet of head to reach the overhead sewer line and my 3 ton AC system may produce up to 1 gal/hr of condensate water if the air is very humid. Either pump will do because because the head and flow rate is well within the capacity of both pumps. Aside: The whole house humidifier was removed with the new central AC because it didn’t work well, so the new pump only needs handle the evaporator coil condensate.
Pump LED Status Indicators
The Little Giant pump doesn’t have status lights which can leave you wondering if there’s a malfunction. An advantage of the Diversitech pump are the LED status indicators:
- Run – Amber LED illuminates when the pump is running.
- Alarm – Red LED means there’s a malfunction and the AC is shutoff.
- Power – Green LED indicates the unit has 120 volts AC power via the power cord plugged into the wall outlet.
The CP-22 pump is available on Amazon.com. I cleaned up the Little Giant pump kept it as a spare in case the Diversitech fails some years down the road.
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