SteveG

A/C people: I think I know the answer, I am looking for some consensus. 134a system. Compressor does not come on, fans do. When I jump the pressure switch, I can hear a vacuum change, engine seems to load slightly, no real change in RPM, but still no compressor. Low side reads high (70 psi) and high is low, about 72 psi. There is a very sticky residue on one of the connections forward of the lines that go into the rear floor boards; other connections are dry. So that would be the leak and the fact that it is soooo sticky, leads me to believe they used stop leak; it held for some lenghth of time, then no more and now has gummed up the works and has plugged the expansion valve which is why the low side is so high; and I'm hoping that is the extent of the damage. The compressor will turn by hand. I did not have time to check if there is 12 volts at the compressor. It worked adequately a month ago and the fans work so I don't think it is an electrical prob. So, fix leak, replace dryer and expansion valve, flush, evac, fill w/good stuff. Comments?

Bill Ball

Jump the freeze switch plug at the same time as the low pressure switch plug. If the compressor does not engage, then it is most likely the infamous headunit relay. It could be other parts of the headunit or the harness, but this is far less likely. Yes, check for 12V at the wire that feed the compressor. If not 12V, feed the compressor clutch 12V directly with a wire run from the jump post. If it engages and shows pressure changes as it should, I would just pull the headunit and install a replacement relay or get a rebuilt headunit from 928Intl.

If the compressor engages with the freeze switch and pressure switched jumpered, pull the freeze switch jumper and reconnect the plug to the switch. If it fails to run then, replace the freeze switch.

cfc928gt

Steve, when the A/C is off the low and high sides equalize so don't let that worry you, in fact it's a good sign that they're equal. Once the compressor starts up the high will pressurize and the low will come down.

dr bob

Steve--

Toyota or P-car?

I did a quick-and-dirty meter diagnostic on a loca owner's car a few weeks ago.

1) With engine off, AC off, AC button not depressed. Lift the rain shield at the base of the windshield to find the anti-freeze switch. Ohm meter, ground one lead, other lead to the freeze switch terminals one at a time. You should see about 4 ohms from both terminals. If so, goto step 4. If you see infinity on one and about 4 ohms on the other., the freeze switch is open and needs replacement. If you see infinity on both terminals, goto step 2.

2) Still engine off, AC off, AC button not depressed. Pull the connector at the freon pressure switch. For those with S4+ cars, this is NOT the little round cannister with the two screw terminals, but rather the switch down lower with the spade terminals. These are on the tubing next to the receiver-drier, front right (pass side on US cars) of the condenser there in front of the radiator. With the connector pulled, you should be able to measure about 4 ohms to ground from one of the terminals in the wiring connector. If you see infinity on both terminals, goto step 3. If you do see about 4 ohms on one wire, pull the ground lead to your meter and use the meter to measure the resistance through the pressure switch itself. If the switch is open (infinite or very large resistance, you are low on freon charge. If the switch is closed (very low resistance), you have a bad or corroded connection at the 14-pin connector under/below the jump start terminal on the inner fender lip.

3) Look for the connection from the front wire harness to the compressor. It's a spade connection, with the male half of the connection captive to that engine harness. On my S4, the connection is right above the air pump bracket and behind the dipstick. The connection there needs to be secure and clean. I took the extra precaution of adding a tie-wrap, and pulled a short loop of the compressor-side wire up under the tie wrap so there is no strain on the wire where it enters the connector. The whole thing is secured around the big harness.

4) At this point, you've determined that there is circuit integrity from the control head wire at the freeze switch all the way to the compressor. This narrows the problem to the fuse, the connections on the control head to the wiring harness, or the infamous compressor clutch relay in the head. If the light in the AC button illuminates when you try to run the AC, the fuse is OK. The wiring to the control head is sometimes disturbed when doing radio surgery; You can verify and sometimes restore the card-edge plug on the rear of the control head through the left side panel on the console, without removing the head. If that's plugged in snug and secure, the relay is the most likely culprit.

Since you've done all the wiring checks to the compressor, take you meter back to the freeze switch. Ground the negative meter lead to the car, and measure DC voltage at the freeze switch. Engine run, AC on, ideally you would see 12V at either freeze switch terminal. With a weak relay, you may see a lot less. You can disconnect one of the freeze switch leads, and test for voltage at both the exposed freeze switch terminal and at the wire that was connected to it. If you now see 12V where you previously saw little or no voltage, the relay is definitely the problem. There are several replacement instructions around on tips pages.

SteveG

All: Thanks for the help. Bob: This is the GTS. We paid commercial rates to get the Sienna fixed. I could not afford the time to remove the dash, that would be because of Pcar demands. They confirmed the dash has to come out to get to the off/on switch. Otherwise it has been relatively trouble free, some burned out bulbs, but next van will be Honda, not Toy.