Is the pressure switch on the a/c dryer a dual high low pressure switch or
just a low pressure switch? It has four terminals and the diagram I have
shows that it is one device with two switches. There is no continuity on
the switch in any configuration which leads me to believe the high pressure
switch is open and the low pressure switch is open at the same time which
leads me to believe that I have a defective switch. Anybody have a source
or part number for this switch. Thank you for any help.



BG
Poteau, Ok

"BG" <techman (AT) alltel (DOT) net> wrote

low to high and vice versa. You need to hook up a manifold gauge set to
properly check the switch.

If you disconnect the connector and look at the terminals on the switch,
think of the terminal closest to the locking tab for the connector as 12
O'clock. Terminal 1 is at 12 O'clock, terminal 4 is at 6 O'clock. These 2
terminals control the magnetic clutch on the compressor. If you check
continuity between terminal 1 and terminal 4, you should see an open
circuit, when pressure is at 28 PSI, then closed up to 455 PSI, then open
again when pressure reaches 455 PSI.

The other 2 terminals at (terminal 2 at 9 O'clock and terminal 3 at 3
O'clock) control the cooling fan. You should have continuity when pressure
is at 220 PSI and open below 178 PSI.

If the receiver/drier pressure switch does not check out, replacement
requires evacuating the refrigerant, unscrewing the switch, lubricating the
O-rings on the new switch with compressor oil, tightening the new switch to
7 ft-lbs, and re-charging the system. Obviously, you need manifold gauges,
an evacuation pump, and purge tanks to change the switch.

Receiver/drier pressure switches rarely fail. What is going on with the AC?
--

Ray O
(correct punctuation to reply)

On Fri, 4 May 2007 23:31:24 -0500, "Ray O"
<rokigawaATtristarassociatesDOTcom> wrote:

And if they'd have spent 25 cents (or less) more on parts, you
wouldn't have to evacuate the system for a simple problem like that.

All it would take is a standard 3/8" SAE Flare fitting (or metric
JIS Flare considering) with a Schrader core valve on the refrigerant
line, and a female flare fitting with a core depressor tit on the
bottom of the pressure switch. Remove the pressure switch, and you
only lose a few grams of refrigerant.

I have to agree with Ray, how long has the AC been dead? (Have you
tried using it at all this year yet?) And when was the last time you
had the AC system serviced?

The Low-High compressor cutout section (terminals 1 & 4) should read
closed at all normal temperatures - unless one of two things is
happening: Either the refrigerant charge is too low for normal
operation, or the condenser/radiator fans aren't running sitting
parked and the system pressure spikes too high while running.

The AC system is going to leak a small amount of refrigerant per
year just permeating through tiny holes in the hoses and past the
compressor crankshaft seal even in the best of conditions, and if
nobody's ever touched it 10 years is rather good for it holding a
charge. Perhaps all you need is a quick servicing and a pound or two
of R-134a refrigerant added. $100 and you'll be fixed up for a few
more years.

Note, DO NOT just buy a can of refrigerant at the Auto Parts and try
adding it yourself unless you have a manifold gauge kit ($50 to $100)
to see what is going on with /both/ the high and low pressure sides of
the system - if you overfill the system something can burst and cause
severe injuries and/or expensive repairs.

You also need to check for leaks using a sensitive electronic leak
sniffer, to make sure the new refrigerant you add isn't going to leak
right out again in a week. Unless you have the budget for $250+
electronic toys, you don't have one. (I do, but then I work on them
often enough to justify having one - so there. ;-P )

And if the leak that developed was bad and the system is down to
zero pressure, air and moisture can get inside the sealed system from
temperature changes. If so, you need to have the leak fixed, then
have the Filter/Drier canister changed (the desiccant inside soaks up
any stray moisture but 12-20 Drops and it's full) and the system
evacuated with a vacuum pump for an hour or two before refilling.

--<< Bruce >>--

"Bruce L. Bergman" <blnospambergman (AT) earthlink (DOT) invalid> wrote

That is one of those great "why didn't I think of that" ideas!

I think we've had the refrigerant re-charged in our '97 Avalon once in the
10 years we have had it. If the OP's Avalon has the auto AC like ours, then
the best thing for the system is to leave it in auto mode year round and
just vary the set temperature. The system will only use the compressor as
needed, and the system will tend to stay more lubricated longer.

Bruce's advice, as usual is great. One other way to find a leak is to have
a shop add dye to the system. Any leaks will show up under UV light. The
dye approach's shortcoming is if the leak is someplace that is not readily
visible, like inside the evaporator housing.

If the OP shares the symptoms with the AC, we can steer him in the least
expensive direction to get it fixed.
--

Ray O
(correct punctuation to reply)

Originally the air conditioning was intermittent. When the compressor would
come on it would cool. Then sometimes the system would come on and just
blow hot air (even with the compressor running. Now the compressor does
not come on unless it is jumped from terminals 1 & 4. When jumped the
compressor starts and there is cooling in the registers but this comes and
goes also as I mentioned so I just have tested for short periods of time to
prevent compressor damage. I believe I may actually have two problems.
I do not read continuity on the pressure switch anywhere. According to
the diagram I should have at least contact from 1 to 4. I should also be
able to read a closed contact on 1 to 2 or 3 to 4 which with both closed
would provide continuity on 1 to 4. The switch cant be reading over
pressure and underpressure at the same time is my reasoning. I have no
closed contacts unless I don't understand the construction of this switch.
The mechanic I am working with also used his scan tool which indicated that
the computer was getting a cut off command to turn the compressor off. I
think this is coming from this ( I believe) defective switch. I think that
once the switch is replaced then I can trouble shoot the intermittent hot
air cold air. Thank you for all of your information.

BG
Poteau, Ok
"Ray O" <rokigawaATtristarassociatesDOTcom> wrote

"Ray O" <rokigawaATtristarassociatesDOTcom> wrote

Guess that my 1991 Camry was an exception. The air condition was never
touched or addded to in the 16 years I had it and it still cooled the car
very well.

"BG" <techman (AT) alltel (DOT) net> wrote

I'll re-post my original advice in case you missed it. You should have
continuity from 1 to 4 if pressures is between 28 and 455 PSI. The only way
you can tell if this is the case is to hook up a manifold pressure gauge,
otherwise you may be making invalid assumptions.

**********
The pressure switch on the receiver/drier detects a change in pressure from
low to high and vice versa. NOTE: You need to hook up a manifold gauge set
to
properly check the switch.

If you disconnect the connector and look at the terminals on the switch,
think of the terminal closest to the locking tab for the connector as 12
O'clock. Terminal 1 is at 12 O'clock, terminal 4 is at 6 O'clock. These 2
terminals control the magnetic clutch on the compressor. If you check
continuity between terminal 1 and terminal 4, you should see an open
circuit, when pressure is at 28 PSI, then closed up to 455 PSI, then open
again when pressure reaches 455 PSI.



I should also be
You should never have continuity between 1 and 2 or 3 to 4.

The switch cant be reading over
I think you are mis-understanding the operation of the switch.

Find a technician with a manifold pressure gauge - that is the first step in
diagnosing an AC problem.

Try jumping terminals 1 and 4 on the harness side of the switch to
temporarily activate the magnetic clutch and look at the sight glass in the
receiver/drier. If you see white foam, the system is under-charged, which
is the most common cause of AC problems.

The intermittent functioning usually indicates either under-charging or
moisture in the system which is icing the expansion valve to the evaporator.
Check refrigerant charge with a manifold pressure gauge. Pressure gauge
readings will tell you what is going on with the system, or at least take a
look and report what you see in the sight glass.
--

Ray O
(correct punctuation to reply)