Accumulator Facts & Tips

Bryan teaches a class about accumulator facts and tips. He explains what they accumulate inside an HVAC system, covers some common problems, and gives some tips on how to use them.

Accumulators are designed to accumulate liquid refrigerant before that liquid can reach the compressor. Liquid should never get inside the compressor. When liquid floods the compressor, it washes out the oil. Many compressors are also refrigerant-cooled, and that refrigerant has to be a cool vapor, not a liquid.

Accumulators are more common in Carrier heat pumps because those systems have fixed-orifice pistons that don't control the superheat. Therefore, the accumulator is an additional safety measure when there is no control over the superheat in a wide operating envelope; it interrupts the liquid before it can affect the compressor. Although the accumulator can become liquid-locked and feed back, it's unlikely. Accumulators also prevent slugging. However, modern compressors are unlikely to slug due to their refrigerant-cooled nature. Slugging happens when liquid gets into the compression chamber.

Overall, getting liquid into the compressor in any capacity is undesirable because it starts foaming the oil and ejecting it from the compressor. The oil lubricates the compressor bearings, which keeps the compressor working for its entire lifespan; premature failure may happen if there is too much mechanical wear without the oil. When oil is ejected from the compressor, it also goes to the rest of the system and can get stuck in the evaporator coil when it gets more viscous.

The accumulator has a U-shaped tube with a small pickup hole at the bottom, which picks up oil. (Oil is heavier than liquid refrigerant and will sink to the bottom of an accumulator.) If that bottom port gets blocked, oil won't be able to get through and will get stuck in the accumulator, so it can't lubricate the compressor. Copper shavings, dirt, and carbon flakes may block that port. There is also a port near the top that stops the accumulator from becoming liquid-locked.

In some cases, oil also may not return to the compressor due to long line sets. Long lines require the HVAC/R technician to add more refrigerant, and special considerations need to be taken to make sure that liquid refrigerant doesn't migrate (or vapor refrigerant doesn't condense to a liquid in the compressor). These strategies include liquid line solenoid valves, hard shutoff TXVs, and crankcase heaters.

When we replace a compressor, we want to pay attention to the accumulator. Replacing the accumulator is perhaps the best practice, especially in a burnout situation, but the old accumulator can be reused if it's flushed and completely cleaned out. It's a good idea to dump out the accumulator and analyze the oil; a lot of contaminated oil indicates a lot of oil loss and could be a burnout. The accumulator is a good place to test the oil, too.

Charging a system with an accumulator is different from charging a system without an accumulator. Liquid charging could result in refrigerant going into the accumulator and getting cold, which makes it hold liquid refrigerant and indicate undercharge because the subcooling won't go up (even though the system could be overcharged). So, using a charging scale and giving the system plenty of time to equalize will help prevent that from happening. With labor, refrigerant, and callbacks being as expensive as they are, the small details matter.

It's also worth noting that motors and electrical parts often fail due to mechanical conditions, not electrical ones. So, burnout isn't always caused by lightning strikes, start capacitors that aren't taken out of the circuit, or over-voltage conditions.

[Captain_Kdawg]

Good video. I knew the basic understand of the accumulator. But I can say I learned about the holes in the pick up tube today !!

[jasonjohnsonHVAC]

Tech tip....accumulators can and do leak....usually from the bottom. Don't forget to check them on a leak search

[TheMylesTheGray]

Please tell me more about hard start kits being negative. I’d appreciate it.

These videos have been enlightening and I have been in this trade for almost 20 years as a refrigeration mechanic, gas fitter, and electrician.

Thanks for the quality content!

[davidryder]

As an HVAC instructor, I appreciated your pain when you asked a simple question and nobody answered.

[enochian]

Mr Brian, thank you for these videos .For some of us studying online these videos are valuable! Your students are lucky to have you as an instructor.

[Harrison]

I give you two thumbs up my friend
I have been a HVAC / Refrigeration technician for over 42 years

[TheBanaxel]

You sir are a honest contractor. Thank you.

[jpstryker]

just started this trade, thank you sir for putting this together in a concise explanation, im going to a school via our union in florida and these classes are helping fill some gaps where i dont fully understand at school. i love the animation, just seeing it helps tremendously.

[mathman]

Love the chit chat with the techs you have now that’s an employer who teaches and strengthens their employee training kudos to you all and for sharing that knowledge.

[adamcox]

I'm considering entering the trade and the amount of information I've learned from this channel for free is incredible. Thank you so much!

[benkuxhouse]

Nice video I’m a technician of 37 years and learned a few things. About the oil test I did a compressor replacement in freezer the compressor was $5000.00 alone Wholesale. Needless to say I came by a few times to do inspection of oil site glass and a few oil acid tests. as he said in this video which is correct commercial compressors can be very expensive

[lynncomstock]

Good job. One correction at 11:06 Liquid will end up in the compressor oil regardless of temperature difference because oil has a very low vapor pressure, and the refrigerant vapor migrates into the compressor oil to increase the vapor pressure of the mixture. (Think of the low vapor pressure of the oil as like a very slight vacuum. It takes quite a while for this to happen. Manufacturers asked that the CC heaters be activated before startup because the bulk of the refrigerant shipped in the equipment will always be in the compressor oil. This is also a reason why compressors have twice the minimum operating oil ensure that they have enough oil under widely varying conditions.)

[nathanhurst]

Thank you so much for these work meeting videos and all the others you do. They are all awesome 👏

[LheodaDjTechTv]

Watching and sending support thanks for sharing

[POlin-qsum]

Great stuff. Coastal Nc area, Blackbeard Country. RustyTanks and Driers blow first, then Coils. A.c.r 30 Yrs. Sometimes I'll wrap a new Tank with black cork tar tape. It will never rust out. Ocean Salt galore. Life is a Beach! Great vids!

[gorrillaback]

This video came at a right time. I wanted more knowledge on accumulators and this video was recommended on the algorithm.

[sparkyobrian]

love these videos, hvac terms are so different than my field, very interesting !!!

[samutokakece]

thank you for awesome and informative knowledge

[ryanmullins]

Just changed a compressor tonight, only to find a bad accumulator, I changed drier, contactor, dual cap, braised with nitrogen, had a feeling accumulator was bad knew I should have replaced it to, now have to recover and either flush or replace accumulator, thought it was mechanical but nope

[mohammadalshaikhhasan]

Thanks Brian, a good topic to attention.

Replacing the accumulator requirs attention about the size.

If you describe little about what could happen when installing a bigger size accumulator in the system.?

Thanks again