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Can you successfully flush evaporator

LS6Fever on Thu July 03, 2014 2:06 PM User is offline

Year: 1992
Make: Buick
Model: Roadmaster
Engine Size: 5.7
Refrigerant Type: R-134a

Originally R12. Converted to r-134a 3 yrs ago and worked great. Now front compressor seal failed and lost oil and some refrigerant and I assume that's why it sent some metal through the system.

Now i have a new compressor, accumulator and orifice. I have been reading up on condenser flushing and this is a serpentine style with larger tubes. (not tiny tubes). So im going to flush that a whole lot with denatured alcohol and follow up with some a/c flush. I have the flush gun to do this with.

My main concern was the evaporator. Are they parallel flow design or serpentine. I cant find anything on this? and I cant tell by looking at it. Also most of the debri/metal should have been caught by the orifice anyways i would think. This is the evaporator in the link.

I just dont want to destroy a new compressor. But dont really want to put anymore money into this car being the age it is. Thanks all.

GM Tech on Thu July 03, 2014 3:30 PM User is offline

parallel flow 5 tubes north 5 tubes south 5 tubes north...

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

HECAT on Thu July 03, 2014 4:25 PM User is offline

Someone just asked me the same question on a Professional Technician site.
So, I cut and paste...Enjoy.

For efficient thermal transfer, Evaporators are often
designed using similar micro channels as a Condenser.
Therefore, the required and capable flushing process would
also be similar.

Since metal debris from a compressor failure is essentially
"filtered" by the Condenser, Orifice (OT or TXV), and
possibly a Filter/Dryer; the amount of debris that gets to
the Evap is usually on the order of metal fines or
"sparkles" . Scroll Compressors tend to
"pop' when they fail; and the high side to low side rapid
decompression tends to throw large chunks of metal debris
back up the Suction Line. For this reason it is recommend to
flush the Evap in the same direction as normal refrigerant

Simple solvent circulating flush machines, RRR flush
features, flush guns, aerosols, and "pour in blow out"
methods are described as simple laminar flow; and will be
subject to follow the "path of least resistance".

This steady (laminar) low flow will find its way thru as
little as only one of the potential 5 or 6 micro channel
paths to the next chamber in the component (Condenser or
Evap). This lack of energy and "path of least resistance"
becomes even more of an issue when encountering debris and
oil residues (buildups) in the micro channel paths that are

Furthermore, due to the lack of velocity; it is almost
impossible for these methods to lift and carry out the
weighted larger metallic particles from the inlet chamber of
a Condenser (when back flushing), or to push them back out
the Suction Line when flushing the Evap.

But the solvent outflow will often show some "sparkles" and
dirty oil; unfortunately convincing (deceiving) the user
that the process is actually working. Obviously it is doing
some good; but in heavy contamination issues from
catastrophic Compressor failures, its not working.

Would you want to attack a driveway cleaning job with a
squirt gun or a pressure washer? I guess anything is
possible (even using a toothbrush) if the time and effort
required is truly of no concern. But someone would surely
proclaim "you can't do that". Just like A/C components are
being proclaimed as not flushable. Why?

1. Simple laminar flow methods are physically limited. They
worked on the simple path of the older tube and fin
components, but not longer with the newer complex component
designs. Sometimes we just have to give up on 50+ year old
tooling technology.

2. Capable (high energy, high volume, high velocity)
flushing processes (HECAT) are deemed as too expensive; even though
this is not necessarily true. Expensive compared to what?
Methods that don't work? Really? Purchasing needed, capable,
and proper tooling is part of staying current in this
business; right?

3. Technicians may not be willing to take the time
necessary; even though proper flushing can be quicker at
times, than component replacement. But somehow, we can
always find the time to do it again. Shortcutting proper
practice such as solvent drying (removal); is nothing more
than just shooting yourself in the foot.

4. With the exception of RRR machine flushing and Ford's
solvent process (IMHO, weak to incapable, as explained
above); OE's don't give us strong support on this topic;
because it is seen more as an aging fleet issue, than a
warranty issue.

5. Aftermarket suppliers are going to support the purchase
of many additional parts with a new Compressor for most
obvious reasons. Compressor suppliers are hoping if you
throw enough new parts at it so the contaminations will be
reduced enough for their unit to survive thru warranty.

...and we call this professional A/C repair?



HECAT: You support the Forum when you consider for your a/c parts.


LS6Fever on Sat July 05, 2014 1:03 AM User is offline

This is a separate question to what i asked before. Also, Thanks for that info.

This is on a 98 dodge ram 1500. I noticed the compressor cycling on and off to often. Air cool but not cold. So i hooked some gauges up and it the pressure would go up to about 40psi when it kicked back on then when it got to 21psi it kicked off. Low side of course. So i added about 1/2 a can of r134 and compressor has stayed on constantly. about 83degrees and 50% humidity. With the low side pressure at 35-36psi at idle speed and 50 degrees at the vents inside.

I just wondered what caused the low side pressure to drop so quickly when the compressor was running when it was cutting off. Obviously it was low on refrigerant, but now it stays around 35psi. Is it supposed to drop to 21 psi eventually and cycle the compressor off?

I really just want a better understanding to why the pressures do what they do? and how often should the a/c clutch cycle on and off when properly charged.

Jag987 on Sat July 05, 2014 2:09 AM User is offline

You have lots to learn my friend, lots to learn. Stick around, do some reading through to older threads and your head will start to spin with all the knowledge that is here.

The very simple version of what you have/had going on is the dodge truck has a leak. The leak is why the low side was low and the compressor kept cycling. The low side hose going into the compressor is also called the suction line/hose. The compressor is "sucking" refrigerant in at a low pressure. If the pressure gets to low, about 21 psi in this case, it shuts itself off. Why you ask? Because along with the refrigerant moving in the system is oil to keep the compressor lubricated. If there is not enough refrigerant flowing, there also is not enough oil getting to the compressor so the low side pressure switch cuts off the compressor so it does not over heat and burn itself up. So no, it should never just drop to 21 and turn itself off, but it does turn off if it is low on refrigerant and drops that low. Now when the compressor is off and no longer sucking, the low side and high side start to equalize pressure. High side pressure can be anywhere from about 150-250+ on a R134 system, but high side is another topic. When the compressor cycles off, high side drops and low side raises. Once the low side rises to an acceptable level (about 40 psi in your case) the low pressure switch cycles the compressor back on, it starts sucking again, low pressure drops, and it kicks it back off. With the correct amount of refrigerant (or close to the right amount), the low side does not drop low enough to cycle the compressor. Now I know there are other reasons (like evaporator temp too low), but there are two main reasons why the compressor cycles off, low pressure to low and high pressure too high.

Now if you would really like to learn more about air conditioning, I would suggest doing a lot of reading here, get a good manual to help like this one, a set of quality manifold gauges and read and learn till you have a good understanding of what is going on then learn some more. You do not always get lucky, half a can of 134 does not always make things work better. I was working on a G6 two days ago, the pressures where way to high to start with. I recovered twice as much refrigerant from the system as should have been there. What was the problem? The compressor electrical connector had come undone. No amount of refrigerant would have ever fixed that. Read and learn and do not be afraid to ask questions.


I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

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