Laurel's Adventures in Home Repair   


Why is My Swamp (Evaporative) Cooler
Blowing Hot Air?



This is one of the questions ALL swamp cooler owners eventually ask at some point least once a season, or
...perhaps several times a season. 

This page will cover as many reasons as I can think of for an evaporative cooler NOT to blow cool air.
1) Relative Humidity Outside of Your Home

Before grabbing that ladder and climbing onto your roof.... What is the relative humidity outdoors?  Has it been raining for three days and you feel like you're living in the tropics? 

Evaporative coolers work at their best in dry weather.  If it is humid outside, forget about it.

Use this handy chart below to determine if humidity is the reason.  You will need an indoor thermometer.  Outside readings for your region can be found online or on most smart phones.

Example:  As I write this, the current temperature in El Paso, TX is 82 degrees.  The relative humidity is 31%.  According to the chart, my inside temperature with my swamp cooler on, should be about 71 degrees.  My indoor thermometer reads 73 degrees.  Off by 2 degrees.  Not bad for late in the season when my pads have more scale build-up and my water tube holes are partly clogged.

Chart used to determine what temperature should be inside with a swamp cooler based on
 the relative humidity and temperature outside

2) Is Your On / Off Switch Turned on Fan (Vent) or Cool?

Many swamp coolers have two main settings.  A fan (vent) setting and a cool setting.  The cool setting turns the pump on at the same time.  Inside your cooler, the pump is pumping water to your pads and the blower is pushing cold air into your home.

If only the fan (vent) is on, then you are just blowing the outside air into your house.  If it is 95 degrees out, that is what you are going to have inside your home.

Typical on-off controls for evaporative cooler

So what is the point of the vent feature?  I use the fan (vent) feature in the evenings to blow fresh dry cool air into the house when the temperatures drop into the low 70's and 60's.  Sometimes it is just nice to have air moving around the house.  Since it is cooler, I don't need the pump on blowing moist air.
3) Water Delivery System.  Is Everything Functioning?

The swamp cooler needs water flowing over some type of pad.  No water = Hot air.

How it Works

a)  Water goes through a water line (copper tubing, poly tubing, a hose, etc)
b)  The water flows through a float valve on the side of the cooler into a basin
c)  A pump sitting in the basin pumps water through a tube to the pads
d)  The water drips off the pads back into the basin
e)  When water evaporates more water comes through the waterline.
f)  The float valve regulates the level of the water in the basin cutting off the water until the basin level drops again, ........and again, and again...........


- Is the water turned on?
- Is the water flowing through the tubing or hose?
- Is the water tube connected to the cooler?
- Is the water flowing into the basin of the cooler?
- Is the water high enough in the basin for the pump to suck up the water?

If yes, to all above then......


- Is the pump pumping water to your pads?
- Is enough water being pumped to the pads

If yes, to all above then go to water distribution tube/pipe below.

If no, then you might need to buy a new pump. First check the tube that goes from the pump to your water distribution system to make sure it is not clogged.  Sometimes sediment or chunks of hard water scaling get lodged inside the tube blocking it.  Clean it out.

Did the pump fall over into the water basin and get wet?  The top part of these pumps need to stay dry.  Only the bottom portion of the pump goes in the water.  If the top part of the pump got soaked, toss it, so you don't electrocute yourself.

Did you or someone buy the cheapest pump available that did not have enough horse power to pump water to your pads?  Before you buy a pump make sure it is powerful enough for your cooler.  You will have to do some research.  If your not sure, have your cooler brand and model number written down before you visit the hardware store.  In swamp cooler regions, the big box stores carry a variety of pumps that cover most coolers. 

Water Distribution Tube/Pipe

The water travels from the pump through a tube to some type of housing that contains some type of tube/pipe that sprinkles, dribbles, oozes, the water over your pads.

The water distribution housing of my cooler holds a pvc pipe with holes in it.  That is it.  The problem with this PVC pipe is that, in hard water regions the pipe gets clogged.  It needs to be cleaned at the end of every summer.  Sometimes, in the middle of the summer season also.  You need to poke something in the holes to open them up.  Run a coat hanger through the inside to scrap off residue.  You can also soak it in vinegar for a few days to soften the hard water scaling.

If your tube/pipe is so clogged up that you cannot get anything through the holes to clear them, you are probably better off just buying a new tube.  Unless you have weeks to soak it in vinegar.

Screw driver used to unplug the holes.

Cleaned up water distribution housing with gray water delivery tube attached on the other side 
The gray tube attaches to the pump.  The whole housing (black thing) sits on top of the pads.

4) Cooling Pads or Media Need to be Replaced?

If the water, pump, and your water delivery tubes are all functioning properly, the problem could be your cooling pads.

The type of cooling pads my cooler uses are the paper waffle things shown below.  They are called cooling media.  To me they are paper waffle things that are a pain in the ass to carry onto the roof.  When I am discarding them, I drop them off the roof to watch them break into pieces.  Easier to throw away when the pieces are smaller.

If your cooler uses this type of cooling media it should be showing some brown color.  If it is totally white and hard as a rock it is time to buy new pads.  The white scaling will not come off without the paper breaking off.  In a hard water area expect to only get 2-3 years out of these pads.

In other words, if your pads can no longer soak up and hold water, you will not have cool air. 

When I winterize my swamp cooler (see how to do this here...) and notice that my pads are shot, I order them online from the Home Depot during the winter and store them until I need them in the spring.  These are a seasonal item so you will only see them in stock during late spring and summer in the big box stores.  So if you need to replace them mid-season you should have no problem finding them.

Swamp cooler pads after only 2 months of use.  A little scaling. Still good.

5) Are All of the Access Doors on the Cooler Closed?

If a door or a piece of your cooler housing is open, you are not going to have cool air.  The cooler works in a box.  If the box is open, the cool air goes out the hole and not into your house.  All you get is warm air.

In August of 2016, my cooler was blowing warm air.  When I climbed up on the roof, I discovered why.  A previously damaged access panel had blown open during some high winds  (see this panel here...).  I reattached it.  Placed bungee cords around the cooler to keep it on.  Ordered a new panel and replaced the damaged panel.
- For information on how to prepare your cooler for winter, please go to this page...
- For information on float valves and how to install them, please go to this page...


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Why is My Swamp (Evaporative) Cooler Blowing Hot Air?
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