USING PURE R-22 IN A SYSTEM DESIGNED FOR R-12.

This note addresses possible implications of using pure R-22
in a system designed for R-12 refrigerant.

* R-22 is a much higher pressure refrigerant than R-12.

Static pressures & Temps
Temp    R12-PSIG R22-PSIG
70F     70       121
116F    150      245

A common "low side" design (test) pressure is 150 PSIG for evaporators,
especially in cars. On a hot conditions, a (non running) R-12 system,
charged with R-22 could easily exceed these pressures and blow out
a fragile evaporator, blow out plug or other weak spot.

When operating, R-12 high sides run at 150-175 PSIG, and R-22 runs
at 230-280 PSIG range.. Again danger of blowing out safety relief
and other weak spots.

* R-22 is a much higher "capacity" refrigerant than R-12.

A compressor made for R-22 for a given temperature use (low, med,
or high temp), at a given horsepower rating, will have much less
piston displacement than (typically 3/5) an R-12 compressor for
the same service class, so they result in equal capacity and
motor amperage draw.  Using an R-12 compressor with R-22 in
the same service class, will result in motor overloading
and burnout as the motor will be overworked at roughly 5/3
of it's rated capacity.

It may be possible to use an EPR (evaporator pressure
regulator) or system "unloading" devices to allow the
compressor to run at 3/5 of capacity (with R-22) so the
net capacity is the same. EPRs or unloaders will hurt total
system efficiencies some though. They may also raise
the compression ratio (see section on R-22 high heat of compression).
Failure to control the evaporator pressure can easily
result in an evaporator which is much too cold and
cause freeze-ups..

It also may be possible to use a compressor designed for
High temp (airconditioning), R-12, to be used with R-22
in low temp service (freezers below 0F). The "lower" the
temp of service class, the larger the piston displacement
for a given horsepower rating.  However, using R-22 in
low temp applications may cause other problems (see the section 
in R-22 high heat of compression).

Ancient open "belt drive" compressors, may have the pulley
on the motor made larger, to slow down the RPM (by 3/5)
of the compressor  so it has the same capacity as it
did with R-12.


* R-22 has a much higher "heat of compression" than R-12.

For high compression ratios (e.g. a freezer or low temp service),
R-22 heats up much more than R-12 does during compression. 
It fact it (in the compressor discharge valves) may easily 
exceed 300F, above this temp breakdown of the refrigerant
starts to occur.  R-22 freezers have long been plagued
with "coking" of the compressor valves, the compressor discharge
line turning black and carbonizing, and all this mess working 
its way to the expansion device, etc. Acids formed from the
refrigerant breakdown eat away at the motor winding insulation
and form "sludge". R-502 was invented to help overcome the
high heat of compression of R-22 in low temp service.

A technique called "liquid injection" also can help here.
A small hand operated expansion valve (needle valve) rated
at about 1/10 of total system capacity, may be used to inject
liquid refrigerant directly into the suction line at a point
near the compressor, to provide pre-cooling of the suction
vapor. Each degree of drop in the suction gas typically also
drops the discharge temp a degree also.

* Refrigerant metering device may need to be changed out.

* R-22 is less miscible in R-12 mineral oil than R-12 is

In short, R-22 does not dissolve in mineral oils as well as
R-12 does, so there may be problems returning oil to the compressor,
if the refrigerant is changed from R-12 to R-22.

Systems  designed for R-22, use smaller diameter suction lines, to
increase gas velocities to help "drag" the oil back to the compressor.
If this isn't done, poor oil return, may result in oil "logging"
in the evaporator, impairing efficiency, and in severe cases, the
compressor may run out of oil, and fail mechanically from lack
of lubrication.  Since may systems do not have an oil sight glass,
this problem is often discovered only after it has already happened,
when it is too late.

This problem may be combated in several ways:
1) use smaller diameter suction lines to get better oil return.
2) change the mineral oil to "AB" (Alkylbenzene) oil which has
   better miscibility in R22.
3) add 5% or so of propane, isobutane, to provide for oil return.
   R-406A uses this approach. (4% isobutane)


--ghg

From: ghg@cidmac.ecn.purdue.edu (George Goble)
Newsgroups: sci.engr.heat-vent-ac
Subject: Re: Freon Breakdown Question
Message-ID: <4394na$hos@mozo.cc.purdue.edu>
Date: 14 Sep 1995 11:46:50 GMT
Organization: Purdue University Engineering Computer Network
Lines: 73

In article <4387pd$sqo_001@grail715.nando.net> pjm@nando.net (paul
milligan) writes:

>	The system runs mainly unloaded most of the time.  The compressor 
>runs very hot ( On a recent mild day, the sump was 130F with no CC heater, 
>the body next to the suction line was 120F, and the head at the discharge 
>line was 220F.  This was on a VERY mild day.  Head pressure was running 275.
>On hot days, head gets up to 350 - 375 - +.  Ouch !!!  I assume compressor 
>temps rise accordingly.

If you have acid, which I suspect you do .. then R22 breakdown is probably 
going on.  Compressor discharge line temps (at the compressor) should
NEVER go over 300F.. or 275F to be safe.. HCFCs start breaking down then.
Although "pure" HCFCs, in sealed glass tubes, may not decompose until 
500F or higher, in real life systems, the oil, metals, etc, act as
a catalyst.. and our tests show around 325F-340F range for the breakdown.
If you unsweat the compressor discharge line, you will most likely
see it caked with carbon as well.  

Scrolls dont have valves, but recips can start R22 breakdown
if the discharge valves hit 325F or so.  The early Copeland
residential scrolls I installed a few years back, all had
"top hat" thermostats (24V) on the compressor discharge to
shutdown on high discharge temps.. which were presumable caused
on low on charge systems (low suction pressure == higher
compression ratio, more heat of compression)
THe reason that home freezers dont use R22 anymore is for this reason.

CFCs like R-12 have slightly higher breakdown temps.. maybe 400F.
R22 has a very high "heat of compression" (that is why 502 was invented).
High compression ratios (ie low back pressure) makes the problem worse.

What are your evaporator pressure/temps?

If the suction pressure at the compressor, goes below 40-50 PSIG,
then you may have high heat of compression problems, causing breakdown.
The hot gas bypass system, may cause high suction gas temps in
certain modes of operation?? like when you are not there??
The "noncondensibles" is probably hydrogen  (R22 is R12 with
one chlorine atom changed to a hydrogen == weaker bond, so lower
breakdown, lower ozone depl, etc)
We have seen hydrogen "form" when running R22 through a gas
chromatograph at slightly over 300F also.

Suggestions:

change the oil, and flush out the system if possible.. get
rid of the acid.. Check the discharge line for carbon buildup.
Run a "megger" ohm test on the compressor windings (to ground)
to check for insulation breakdown.. good should be over 100
megaohms..  If less than 50-60 megaohms, then insulation may
be damaged with a "burnout" failure to soon follow.

As you said, try liquid injection at the compressor.. I have
read, that for every degree the suction gas can be lowered,
the discharge is lowered 1 degree also. IF it were me, I would
not put a TXV there, but get a "superior" hand expansion
valve.. They have red knobs and look just like the packless
liquid line valves, but they are needle valves, so you can
adj it.. get the 1/4" size.. cost is about $40. (double a similar
liquid line valve).. This way you can set the amount of inj
you want.

Get a discharge line gas temp protector device.. and set it
for 275F or less.. just a clamp-on temp sensor for the discharge
line and cuts out if over 275F.

If you can deal with flammability issues, change the refrigerant
to R-290 (propane).. heat of compression much lower than R22, 
no breakdown problems.. drop-in for 22.

--ghg
http://ghg.ecn.purdue.edu
http://worldserver.com/R-406A

From: ghg@cidmac.ecn.purdue.edu (George Goble)
Subject: Re: Contaminant Removal
Message-ID: <4qoc1t$p8s@mozo.cc.purdue.edu>
Date: Jun 25 1996
Newsgroups: sci.engr.heat-vent-ac

In article <4qjvjk$mo5@news.enterprise.net> davida@enterprise.net
(davida@enteprise.net) writes:

 >I am about to tackle the follow situation and am looking for opinions.
 >A supermarket rack operating on R22 running ice-cream/frozen food. The
 >problem I am told is that the sytem expansion valve inlets are being
 >blocked with a containant, believed to be the result of an engineer
 >adding mineral oil when the rack is designed for synthetic (PAO) oil.
 >I have been told that the oil has been removed and replaced with the
 >correct brand twice,although I suspect that only the compressor oil
 >was replaced, leaving the separator oil. Filter/driers have been
 >changed as have oil filters. Liquid liner driers have been added to
 >individual cases, two way driers to enable liquid return on saturated
 >gas defrost, but the driers have been breaking up. Information that
 >concerns me at the moment is that the rack apparently has to operate
 >at roughly a 250psi condensing pressure to ensure a positive liquid
 >supply to the cases. For those that know of it the system uses a
 >Hussman Turbashed type oil separator.
 >Any opinions.

 
My $.02 .. Unless this system is multi-stage compression (with intercooling
between stages) or uses liquid injection into the compressor inlet
(to keep discharge temps down), then this system is probably a wreck already.

R22 cannot be used, in most cases below 20F or so evaporating temp, due
to it's high heat of compression and temps over 300F being produced
in the compressor discharge valves. This is why R502 was invented.
R22 was tried in home freezers years ago.. There were many failures from
the cap tube becomming plugged with carbon from R22 breakdown.

The Breakdown also creates acids which break down drier cores, eat away
at motor winding insulation (if internal motor), cause copper plating,
break down the oil, form "sludge".  I dont think some mineral oil
in the system is going to make it any worse than it already is.

Was this some R502 system, that somebody just charged R22 into?
I would run away from this one.

--ghg

From: ghg@cidmac.ecn.purdue.edu (George Goble)
Newsgroups: sci.engr.heat-vent-ac
Message-ID: <4r098c$l9u@mozo.cc.purdue.edu>
Subject: Re: Contaminant Removal
Date: 28 Jun 1996 09:39:24 GMT

In article <125@fridgemech.win-uk.net> mlobrien@fridgemech.win-uk.net
(Marc L O'Brien) writes:
 
>In article <4qoc1t$p8s@mozo.cc.purdue.edu>, George Goble
>(ghg@cidmac.ecn.purdue.edu) writes:
>>In article <4qjvjk$mo5@news.enterprise.net> davida@enterprise.net
>>(davida@enteprise.net) writes:
>> >I am about to tackle the follow situation and am looking for opinions.
[snip]
>>My $.02 .. Unless this system is multi-stage compression (with intercooling
>>between stages) or uses liquid injection into the compressor inlet
>>(to keep discharge temps down), then this system is probably a wreck already.
>
>What about, or if the compressor motor is not suction cooled.
>
>>R22 cannot be used, in most cases below 20F or so evaporating temp, due
>>to it's high heat of compression and temps over 300F being produced
>>in the compressor discharge valves. This is why R502 was invented.

R22 breaks down just above 300F.  You get HCl, HF, R12 and other things
being produced.  Most other HFCs would be similar due to the weaker
hydrogen bonds.  Motor cooling or not.. same thing.. Oil sludges from
all the acid and partly breaks down.  Carbon everywhere.  If motor windings
are in contact with the refrigerant, they may fail also.  When the suction
pressures are below 20F evaporator pressures you are in danger of 
hitting 300F in the discharge valves due to increasing compression ratio.
Liquid injection or multi stage compression must be used to prevent 
hitting 300F.  

POE oils cant even hold their own in newly built equipment, let alone
with refrigerant breakdown going on. Steel is a catalyst to cause
POE's to break down.. Mfgr's add "passivators" to try to counter this
effect.. but they are not always perfect.. High temps greatly increase
the speed of breakdown reactions of the POE oil.

--ghg