Our downstairs A/C (heat pump) went out the night of a bad July thunderstorm. The next morning we called our local Trane A/C repair company and they (thankfully) made it out here in only about 3 hours. That was the good news. The bad news was the A/C compressor was burned out, probably from voltage drop during the storm.
Our serviceman, Walter, had to replace the compressor and would not be back with the parts until the next morning. Even though the compressor was under warranty (thank you Trane for the 10-year warranty on the compressor) it still cost over $900 for the two service calls, the 2nd one being about a half-day. Here are some interesting facts we learned from Walter.
1. How to tell if your heat pump is cooling correctly
This trick is a good way to keep an eye on the health of your heat pump without expensive spring and fall service calls. With clean air filters (or better yet with NO filters in place), and on a normal day with respect to heat and humidity, place a cooking thermometer in the A/C vent and give it a couple of minutes to come to temperature. Write down that temperature and then put the thermometer in the air return vent and, again, give it a couple minutes. Subtract the temperature of the cold air coming out of the vent from the warmer temperature of the air going back in the air intake. The difference should be in the range of 15-18 degrees. For example, the air out of the vent is 58 and the air temp at the return is 73, you have your 15 degrees of difference.
Note: Some of the newer high efficiency systems have a smaller difference – they move more air to cool the same amount. Overall, your cost per degree of cooling is still lower.
If you do this test monthly and begin to notice a decrease in the temperature range, first check your filters. If, after replacing or removing the filters, you still do not have the normal amount of difference between incoming cool air and the return air, you may be starting to get low on refrigerant. If more tests over the next couple of days confirm a drop in temperature difference, shop around and find someone who can top off the refrigerant and check for leaks.
Note: Your normal temperature difference may be 14 degrees, it may be 19 degrees. What is important is to understand what is normal, and to monitor it for a change that may indicate a problem.
2. Expensive, high efficiency air filters reduce cooling and cause your system to wear out quicker
Anything that restricts the free flow of air in your heat pump system ( the type of whole house cooling most people use) reduces efficiency, drives up your electric bill, and produces additional strain on the system causing it to wear out more quickly. High efficiency filters that fit in the air return vent trap a lot more pollen and dust, but they cut air flow significantly. Heat pumps were made to cool or heat your house, not be an air purifier. The purpose of a filter is to keep too much dust from building up inside the ducts, on the fans, and on coils.
Walter advised staying away from the cheapest blue fiber filters and go one step up to the ones that are generally white. I think they are made from spun fiberglass. Rather than spend money on an expensive filter every month, buy 2-3 cheap filters and change them as often as every two weeks. Not only will you save money on filters, but you will reduce your electric bill and repair costs.
If you have a dust problem, an odor problem from pets or smoking, or if you have allergies, use the money you save to buy a real air filer. Let the heat pump do the job it was designed to do; buy a system like this Air Filter System – Air Purifier to clean the air. The air will be both cooler (or warmer), and cleaner if you do.
3. When the AC guy comes to do an annual check of your system, take the filters out, or make sure you have brand new filters installed.
On Walter’s initial service call, I asked him to take a quick peek at the upstairs unit to make sure it had a good charge of refrigerant. Since I had just paid him $105 to tell me there was nothing he could do that day and he would have to come back, I was concerned because the upstairs temperature would creep up during the day from 76 to 86+ degrees, despite the A/C running non-stop with the thermostat set to 76. He checked it, and it was fine. During his visit (but after the A/C check), I removed all the filters from the return vents to see how much different the system would run without my allergen and pollen filters.
The next day when he returned, he replaced my compressor and (for some reason) checked refrigerant in both systems. To my surprise (less his), the system was 1lb low on refrigerant. The difference was due to the restricted flow in my air filter. I say all that as background for my comment that you need to remove or replace filters before you have the refrigerant checked or you may be low and not know it.
4. How to maximize cooling efficiency if your heat pump is having a hard time keeping the house (or upstairs/downstairs) cool
This is pretty simple: Keep your filters clean (airflow = cooling) and leave the fan running; do not put it on auto. Running your fans all the time is often better than putting them in the auto position for several reasons:
- It keeps the air mixed, reducing hot/cold spots
- It is actually less wear and tear on the fan motor in hot or cold weather to keep the fan running than having it constantly starting and stopping.
- It also takes lot less electricity to keep it running than to get it running.
The proof is in the pudding, as they say. I mentioned above that our upstairs unit could not keep up with the heat load during the hot summer months. Since I replaced the fancy (and expensive) air filter and left the fan running around the clock, its been a constant 76 degrees upstairs.
One last tip: Keeping the humidity down with a whole house dehumidifier can make the temperature feel cooler.
Thank you Walter!