In this Ask Derek Cole Show episode, Derek answers listener questions about common HVAC problems. He explains that an air‑conditioner freezes primarily due to two factors: restricted airflow—often caused by high‑efficiency (high‑MERV) allergy filters that choke the system—and low refrigerant levels. He stresses regular maintenance, clean coils, and timely filter changes to prevent freezing. When asked about pricey allergy filters, Derek notes that while better filtration is beneficial, overly restrictive filters can impede airflow and cause freezes; he offers a practical rule of thumb—if a filter is hard to pull out or its corners cave in, it’s too tight. He also advises replacing filters every 30‑45 days or when visibly dirty. Regarding a manufactured home with a gas furnace, he explains that AC can be added by installing a coil and outdoor unit, or a heat‑pump can be paired with the existing furnace to create a dual‑fuel system, providing both electric heat‑pump efficiency and gas backup. He confirms this approach works in various climates, not just North Carolina. Throughout, Derek balances technical advice with a conversational, slightly humorous tone, aiming to give homeowners actionable guidance while warning against over‑optimizing filter efficiency.
Questions this video answers
It freezes mainly because of restricted airflow—often from an overly efficient allergy filter—or because the refrigerant level is low. Dirty coils and lack of maintenance can also contribute.
Better filters are beneficial, but if they’re too restrictive they can cause airflow problems and freezing. Choose a filter that balances particle capture with airflow, check that it pulls out easily, and replace it every 30‑45 days or when dirty.
You can add AC by installing a coil and outdoor unit onto the existing furnace, or install a heat pump to create a dual‑fuel system where the gas furnace serves as backup.
The dual‑fuel concept works in various climates, not just North Carolina; it’s applicable in places like Wyoming as well.
Why does my unit freeze?
Unit freezes because you bought that expensive, expensive allergy filter and now I can't breathe. Hey, what's up? We are throwing it back today to episode 45 of the Ask Derek Cole Show. Uh, very important because we're talking about AC freezing this time of year. Something very common that happens is there's frost or ice on your AC unit. Why does that happen? Check out episode 45. It is years ago, so my speech is a little better than today with my MS, but good information. Keep watching.
Why does my unit freeze?
Unit freezes because you bought that expensive, expensive allergy filter and now I can't breathe. No, I'm just kidding. But no, that could be one of the situations. You could have too good of a filter and the air can't get back to the unit. If airflow is a challenge, it will freeze over because airflow is a challenge. Also, it will do it because of low refrigerant. Those are really the two big reasons you have that freezing problem. If you're low on refrigerant, it will freeze. Airflow problem, it will freeze. Those are really the two main things. Could be, you know, some minor things inside of that, but those are really the two biggest things. We saw a lot of that in the summertime, a lot of freezing units, and it was because of stopped-up coils, filters, and it was just lack of maintenance. So again, if It's important to do the maintenance on the system and change your filter because the service calls could have been prevented with that happening.
Are the Allergy Air Furnace filters worth the extra money?
I know the answer to this question, but it really, I mean, I hate to say it, but it kind of depends on what you have at your house. And what the situation is. The better filter is helping, but you can go a little too far and get too good of a filter, and then you have an airflow problem which will cause the unit to freeze and cause some other issues. So it kind of depends on your situation. When our techs go out to the house, they can recommend what's better for you. But I would, yes, you need a better filter than the 69-cent Home Depot see-through filter. I mean, if you can lay it on your table, take salt, pour it over it, and the salt gets through, that's not a good filter. That makes sense? Because you're trying, I mean, the big filter is stopping, or the cheap filter is stopping things like sandwiches and chickens and any kind of furry pets from coming through, but it's not stopping the small particles that you need to be stopping. And that is 98% of your problem is the small ones, not the big ones. So that's what you need to be focused on. So the better filter is better for you, but you do have to walk a fine line of, uh, restricting airflow and stopping the particles. Now, there are air cleaners on the market that can handle both. We have them, but you just have to be careful about— not wish— I'll tell you a good sign. So when you put the filter in the return and the unit's running, if it starts to cave in a little bit and the corners cave in a little bit, the filter is too much for that unit. It is too tight because now you're caving it in a little bit and the air is still going around the corners. So I mean, you defeat the purpose. It's not, it's not going into the filter anymore, it's going around the filter to get to where it's going. So you know, you should give a gentle little tug to get it out. Um, you shouldn't have that much force to get it out. So that's kind of a rule of thumb. I kind of hate rule of thumbs, but there you go. There's one of them. So if you have— I mean, if you have to like, you know, lean against the wall to get it out, that is a problem. But if you have to just, just pull a little bit, you're good to go. Okay, so the answer is it kind of depends on your system. I really hate that kind of an answer, but It depends on your duct system, it depends on your setup, depends on all those factors into making sure you have the right filter. But regardless of the filter, the most important thing you can do is change that on a regular basis. If you go 30, 45 days and there's no dirt or anything on that filter, That is the indication to know the air is bypassing that filter because it's not even dirty a little bit and it's getting to the unit and we have another problem.
My manufactured home has gas heat and I'm wondering if installing air can use the same system or if it needs to be a completely different system.
So good question. What usually happens on a mobile home is you have a gas furnace or a Leisure Furnace in the closet. You open a little closet, you're like, hey, there it is. So what you can do is actually add air conditioning to that with a coil and with an outdoor unit. Um, so you could use that existing furnace most likely and just add AC to it. Um, or you can do what we do a lot of, which is add the AC to it, but instead of an air conditioner outside, you have a heat pump outside. So now you're actually creating a dual fuel system. You have a heat pump outside and you have a gas furnace inside as your backup source. So instead of electricity, you're using gas as backup. So it's really the best of both worlds. So yes, you can add AC. I would go ahead and kick it up a little bit more and make it dual fuel.
Is that mainly for here in the, like, in North Carolina where we're at, or is that in general? Because I know the person that asked that question lives in Wyoming.
You don't see too many gas furnaces here. You see a lot of electric furnaces, but it should be the same in Wyoming. Okay, I was just curious if it's the same kind of manufacturing.
Like, we use more heat pumps here than like—
yeah, I mean, we run into a few of the gas furnaces in the mobile homes. It's just not— it's just kind of rare for this part of the area, country, state, turn to a gas furnace, so move on. But it does happen, and when it does happen, we have, you know, converted those over to a dual fuel system, which saves you a ton of money because they use whatever— if it's electricity or gas, depending on temperature outside, it switches between the two. So it's really efficient as to using the best source of heat for what the weather calls for. So if you have a 50-degree day in Wyoming, you will use heat pump heat. If you got a 20-degree day in Wyoming, you'll probably use your gas. So it's going to use the best of both. That's it. That was a good one. All right, episode 45, um, done. So, uh, yeah, appreciate all the sharing, man. Facebook has been lighting up with people tagging other people on the little post and sharing. Really appreciate that, so keep it going, and we will see you next time.
