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.
The pressure switch on the receiver/drier detects a change in pressure from 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?
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.
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.
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" wrote in message news:d53c9$463c2263$47c2b532$ snipped-for-privacy@msgid.meganewsservers.com...
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.
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.
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