I am not licensed HVAC professional.

My HVAC is not blowing cold air. Last year I called one guy and he said that it was low on refrigerant, refilled it, AC started working. After a year, I have same problem.

Asked few contractors, they are saying that refrigerant leak is more common near evaporator coil. According to them, If coil has rust, it needs replacement. They are charging me around $250-300 just to come and look at the coil to confirm. They can't tell me how much it is going to cost to repair it until they look at it.

I understand that these technicians have knowledge and they deserve the price they are asking for their service.

I recently lost my job, I was wondering if there is a way I can unscrew the AC panel, and can visually inspect the coil to confirm their suspicion. It would save me around $300 bucks and I can directly request repair estimates.

Here are the pictures of my HVAC.

I took 2nd picture from that small service panel door(blue arrow in 1st picture), hoping that I will be able to take picture of coils, but looks like they are covered.

I was thinking to open the screws, in 1st picture to inspect coils, and may be take pictures and share with my contractor so he can confirm. I am not going to touch anything inside the panel. Just want to open, take few pics, and close it back. Is it safe to do it ?

Evaporator model 4txcb025bc3hcaa which is an R410A unit.

enter image description here

enter image description here

  • @keshlam - rust. Contractors told me if coil has rust, it needs replacement. Commented May 21, 2023 at 23:08
  • Right; just noticed that's in your problem statement. Sorry.
    – keshlam
    Commented May 21, 2023 at 23:09
  • 8
    I think it's a safe bet that there's a leak if they guy came out last season, filled it up, and now it's low again. Having to fill it last year is a good clue, having to refill it again this year pretty much confirms it. They used to have a product that they'd put it which would include a dye to reveal the source of the leak as well as a sealant to (with some luck) plug the holes for a year or so until the coil could be replaced. I don't recall the name of the stuff or if it's still used, but you might look into that.
    – gnicko
    Commented May 21, 2023 at 23:42
  • 1
    It's safe to open the panel if you turn the breaker off, and you should do that annually to clean inside there. But looking for leaks yourself is a waste of time. As others have said ... you clearly have one, and you can't fix it yourself.
    – jay613
    Commented May 22, 2023 at 22:38
  • 1
    @gnicko it's just called "UV dye". A professional will look for large leaks using a leak detector and if none found will recharge the system adding the dye to look for small leaks. The system will run for at least a few weeks, then be inspected with a UV light to look for stains around tiny leaks.
    – jay613
    Commented May 22, 2023 at 22:42

4 Answers 4


Yes those covers can be removed for inspection or cleaning. There won't be much more to see than what you've already seen, but at least you'd be able to see it more closely.

Yours is an A-shape coil, so named because when viewed from the end it looks like an A. The "coils" are the parts circled in yellow below. Tubes around 1/4" or 6 mm diameter run through the fins visible in the photo. At each end of the coil there are "elbows" like a macaroni noodle connecting one tube/row to the next.

evaporator coil

Evaporator coils are often made of aluminum because it conducts heat well - and doesn't rust! The technicians you spoke with who said if it's rusty it needs to be replaced must have misspoken, or been misunderstood, because the refrigerant-carrying parts of a coil aren't made of ferrous metals. Sure, there can be some steel sheet metal included in the assembly, but rusting of that stuff won't contribute to a refrigerant leak.

If you remove the cover that'll give you a chance for a better look. In addition to refrigerant, the system also contains oil to lubricate the compressor. A leak often will leave evidence in the form of an oily residue. This is something you can easily look for on all the components: the evaporator shown here, the connections to the copper line set indoors and outdoors, around the service valves and coils of the condenser, and on the body of the compressor itself.

If you've only tried calling the contractors who advertise heavily, then try asking neighbors, friends, or other associates for a referral of a sole proprietor or "mom-and-pop" small contractor. They may be willing to do inspection/evaluation at a price that's more agreeable to you.

  • 1
    Is it advisable to spray soapy water and look for bubbles? Commented May 22, 2023 at 14:05
  • 4
    Is it worth shining a UV lamp on it in case leak detecting dye had been added to the refrigerant? Commented May 22, 2023 at 14:30
  • 1
    @user253751 It seems that some soaps can be corrosive to aluminum. I would think that a refrigerant leak would have to be pretty significant to show up under the soapy water test, so it's probably not an effective test.
    – Greg Hill
    Commented May 22, 2023 at 16:44
  • 2
    @AndrewMorton Sure, a bit of UV exposure likely won't hurt. It's probably a long shot, though. UV dye is not routinely added to a system because adding it reduces the cooling capacity of the system (it takes the place of some of the refrigerant, but does not contribute to cooling like the refrigerant would have). It is possible, though, that a technician previously struggled with this system and chose to add dye.
    – Greg Hill
    Commented May 22, 2023 at 16:49

There's not much to look at when you remove those panels. The technicans will usually pressureize the coils and then spray or brush some leak detector and look for leaks. They might pump the coils up with a colored dye and look for leaks. If you're already low on refrigerant, you won't be able to find any leaks yourself. If there are leaks, they will be much smaller than a pin hole. It is safe to open those panels but you'll want to turn off the breakers and/or open the disconnect switch.


It lasted only a year instead of many years. If it went low it has leaked. Where and can it be repaired only a professional can do that test not you. Looking at it will not reveal the leak, one needs testing equipment for that.

Get the model number from that coil and start shopping. Take look at the refurbished market they are a fraction of the cost.

I would start with determine the problem of not cooling.

1- Is the compressor running ?

2- If yes, get a professional to find the leak - it might not be the coil, it can be outside or anywhere

3- can the leak be fixed

  • 2
    It seems important to note that even if a homeowner saves money on buying a refurb or aftermarket coil a specialist will still have to be engaged to fill the system. It may be possible to buy or rent the specialized equipment and refrigerant. In any case there may be more costs to consider beyond just replacing the single part.
    – Freiheit
    Commented May 22, 2023 at 13:42

You have an R410A refrigerant system. You don't have the scary supply problems of R22 systems, but R410A is still illegal to self-service - you need not only a refrigeration handling license (not terribly hard) but also the recovery equipment and upward supply chain to recycle refrigerants, so finding a vendor willing to work with a pro-am DIYer. Even if you plan to simply add refrigerant, you need to be able to recover and recycle if anything goes wrong.

Now two products are sometimes used in pursuit of leaks. One is a dye which is added to the refrigerant. Where it leaks, it leaves dye traces visible under ultraviolet light. The company you used last year may have employed the stuff, so it may be worth searching the system with a UV light.

The other is sealant, which is quite poorly regarded within the industry as a last-ditch stop-gap used by amateurs and hacks - such repairs do not tend to hold for long, and they tend to do long-term damage to the system. (which of course works great for the installer, by creating demand for new systems).

This for sure: something will need to be repaired/replaced and you are unlikely to get out of this for under $500. If that's not in the cards right now, A/C is, after all, entirely optional and you can simply try to be out of the house in late afternoons, or open windows for cross-breeze.

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