So, what can I say "correctly" to find out how to bypass the pressure
switch. Am adding 134a after compressor change and dryer change and
orfice change. Have pulled vacuum down, but need the compressor to
engage so I can pull more 134a (not freon) into system. Do you know
how to do this?
Well good. from the sounds of things initially, you were about
to add the wrong refrigerant.
Engaging the compressor will not "pull" more refrigerant into the
Yes I do. It is done by making the pressure inside the vessel of
refrigerant higher than the static pressure in the vehicles AC
If the static pressure is not high enough to close the low side
switch, there isn't yet enough refrigerant in the system to carry
the necessary lubricant to avoid a compressor failure.
(you do know that the refrigerant carries the lubricant, don't
To raise the pressure inside your charging vessel (jug or can)
you need to heat it up.
Hot water usually will suffice. It will be a little slow, and
you'll no doubt need to make numerous trips to replenish the hot
water to accomplish what you need, but thems the breaks when you
don't have the correct equipment.
Say "thank you Neil" because I just saved you from screwing up
your brand new compressor.
Sorry if this sounds a little terse, but these systems are so
damn fragile that if you don't follow proper procedures, they
tend to be very short lived.
Oh yeah... I hope you used the correct oil in the correct
amounts and distributed it into the correct components in the
proper proportions, unlike another poster in a different group.
Ok. So, I guess I could just plug in my charging cylinder to push the
134a in then.
About the oil,
I added 8 oz to the compressor and 2 to the orfice.
Any more advice before I say "thank you Neil"?
The total oil capacity for the entire system is 8 ounces.
8 ounces inside the compressor is an awful lot...
I'd have put 2 ounces in the compressor, 2 ounces in the
evaporator, 2 ounces in the condenser and 2 ounces in the
At this point, you should attempt hand turning the compressor to
make certain that it's not hydraulically locked before you apply
power to the clutch.
With the can stood upright, gas will be discharged, invert the
can (tapper down) and liquid will be discharged.
If recharging via a 30lb jug, it's vice versa.
In the inverted state, if ambient temperatures are high enough,
by the time the refrigerant reaches the low side service port,
it'll probably already have changed to gas.
When refilling the system via the low side service port, you DO
want the refrigerant to be in a gaseous state. The low side of
the system is the inlet to the compressor and compressors of this
type do not tend to handle the intake of liquids very well.
I read some more and finished the job tonight.
I replaced the compressor, due to bad bearings. I added 9oz (per
manual) 150 visc. oil.
I took it down to a vacuum 29 +- 1 for 35 minutes, let it stand for 5
On the high side, I used a charging cylinder. Measured in 1.9 lbs of
liquid. I then released it into the high side until it slowed, then
in the cylinder heater and emptied it into the car.
I let the car sit another 15 - 30 minutes while I reinstalled air
Started engine, clutch engaged, pressures were as in the spec sheet,
I used to help my dad in his garage years ago using freon, and we had
bypass the pressure switch to get the thing to take freon WITH the
running. I just assumed the same went today. Actually, had I not had
access to the charging cylinder, I would have had to force the freon
the low side as a gas somehow, I thought.
Well, thanks again for your fine advice.
In all seriousness, this is a dangerous task. You could be injured or
killed. I am reluctant to provide information that could injure or kill
you if used incorrectly. By bypassing the switch, it is possible to put
so much pressure on the refrigerant cylinder that it bursts.
I become increasingly suspicious that you don't really understand the
workings of the system and should have it serviced by someone who is more
familiar with a/c systems and how they work.
Jim, I agree with this answer. I am also wondering how you added 2oz of
oil, PAG oil I trust, to the orfice tube? It should have been added
into the accumulator. Do you know for sure that the total oil capacity
is 10oz? Are you using a gauge/manifold set to do this refridgerant
Go have the code cleared. Once you get a low refrigerant code, the
compressor will not turn back on until it is cleared. It will not engage the
compressor clutch relay and for good reason. Do not turn the air back on
after having the code cleared until you have the 134a hooked up to the
An asshole with a can of refrigerant in his or her hand, may very well soon
become a dismembered and dead asshole, with an exploded can of refrigerant
in their missing hand!
Heat the can, to raise the temperature of the gas in the can, in a can of
hot water from the tap, and you'd be surprised how fast it goes in the high
side. With the engine off!
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