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No power to clutch! Have power to relay??

Teehee on Wed August 05, 2015 10:12 AM User is offline

Year: 2005
Make: Toyota
Model: Sienna
Engine Size: 3.3
Refrigerant Type: 134A
Ambient Temp: 90
Pressure Low: 110
Pressure High: 110
Country of Origin: United States

This has been exhausting! Trying to diagnose, possibly multiple issues here....AC stopped blowing cold while on a trip. I was passing someone on the interstate and happened to notice my van's AC blowing warm air. I pulled over to check everything and found the clutch not engaged. I swapped the relay with the horn relay with no luck. After I got home I began to troubleshoot...I have 12V at the clutch relay on both the clutch side and the control side. When I jump the relay I get power to the clutch, with no clutch engagement. So it looks as if I have a bad clutch coil, but why am I having to jump the relay to get power there? From the info that I have, the static pressures that I have now, should enable a good pressure switch to complete circuit?? I just don't know what else to look at. I took it to a shop and they told me I needed a new compressor....when I said how can you tell when there is no power going to the clutch, he just said a new clutch will fix that!!!! How is a new compressor/clutch going to magically feed power to itself, without diagnosing the underlying problem here. Please help if you can. Thanks

Teehee on Wed August 05, 2015 10:33 AM User is offline

Looking at a schematic it looks like I need to check the ambient and evaporator thermistors...I checked the ambient which seems fine (resistance changes when temp changes and temp display in van works), but the one on the evap, I don't know where to find it?

mk378 on Wed August 05, 2015 10:38 AM User is offline

If the clutch doesn't engage when you jump power to it, there is a problem with the clutch. If the coil is open circuit (resistance should be 3 or 4 ohms), it is bad. Assuming the coil is OK, usually you only need to take some shim washers out to reduce the gap between the plate and the pulley.

Never jump the clutch with the engine running, this risks an overpressure because the computer doesn't expect the compressor to be running and may not turn on the condenser fans.

Late model cars are designed to self-test all the control systems through the computer. This may require the scanner that only dealers have though.

Teehee on Wed August 05, 2015 10:48 AM User is offline

I've pretty much determined that the clutch is bad and will need to be replaced. It seems like the real issue is the ECM not letting power get to the clutch either because of an issue with the amplifier, thermistor, pressure switch or ECM? I don't really know where to start. Is the thermistor hard to get to on these? Anyone familiar with Toyota Sienna's?

Teehee on Wed August 05, 2015 12:59 PM User is offline

Someone sent me a troubleshooting schematic for the Sienna, it says that the pressure switch should have continuity between 28psi and 455psi, I have 110psi static and no continuity. Should I go ahead and replace the switch or is there another way to test it?

Teehee on Wed August 05, 2015 1:18 PM User is offline

Someone sent me a troubleshooting schematic for the Sienna, it says that the pressure switch should have continuity between 28psi and 455psi, I have 110psi static and no continuity. Should I go ahead and replace the switch or is there another way to test it?

mk378 on Wed August 05, 2015 1:55 PM User is offline

Two-wire on-off type switches can be bypassed by jumping the wires on the car side, as long as you are standing there to watch the pressure. Refrigerant needs to be taken out to replace the switch.

Cussboy on Wed August 05, 2015 2:05 PM User is offline

Quote
Originally posted by: mk378
Two-wire on-off type switches can be bypassed by jumping the wires on the car side, as long as you are standing there to watch the pressure. Refrigerant needs to be taken out to replace the switch.

Yeah, and you need to jump the switch only a second or two to see if that engages the compressor. Or just check for 12 volt positive going in, and see if there's 12 volt positive coming out. If mk378 says that on that model that the refrigerant must be recovered to replace that switch, he likely knows for sure.

Teehee on Wed August 05, 2015 9:31 PM User is offline

At this point I'm just trying to get 12 volts to the clutch. Is the dealer the only one who can diagnose and replace a bad ECM? When I jump the relay and get 12v to the clutch, nothing happens so it's safe to assume the clutch is bad. If I were to replace the clutch/compressor, I'd still be in the same boat...no power to the clutch unless I jump the relay.

mk378 on Wed August 05, 2015 10:07 PM User is offline

You said the pressure switch was open. I don't know that exact model but if it is a 2-wire switch it should be closed at normal pressure.

Three-wire "switches" are actually sensors that should NOT be probed or jumped because ECM damage may occur. You have to scan the computer to check if those are reading properly.

Check the clutch coil for resistance. Also check the ground connection. If OK-- with engine off, jump the clutch and then press on the plate. If that makes the plate snap down to the pulley you need to reduce the gap.

Edited: Wed August 05, 2015 at 10:09 PM by mk378

Teehee on Wed August 05, 2015 11:08 PM User is offline

The pressure switch has four wires, 2 for the high/low psi for the clutch and 2 for the high/low psi for condenser fan. It was the fan side of the switch that was open, the clutch side has continuity. I'm concerned that this is an ECM issue, but don't know what else to check

Edited: Wed August 05, 2015 at 11:13 PM by Teehee

Teehee on Thu August 06, 2015 9:58 AM User is offline

AC amplifier....are these known to cause issues?

mk378 on Thu August 06, 2015 10:39 AM User is offline

Can you post the schematic? It sounds like this is an older style system with logic levels on dedicated wires instead of a CAN bus. If it is that style system there is a wire going into the ECM from the amplifier to command the A/C to come on, and one coming out to ground the relay coil when the ECM sees the command come on and other conditions (like engine rpm) are considered OK to engage A/C. You can probe those wires to see if the amplifier is issuing the command and the ECM is responding to it.

First you need to be sure that the compressor will engage if the relay pulls in. It seems unusual that two things would fail at the exact same time.

Teehee on Thu August 06, 2015 10:56 AM User is offline

The failure occurred during a WOT (wide open throttle) condition, but I have been told that this system doesn't have a cut-out relay. Couldn't the logic within the ECM or amplifier control the clutch based on the position of the throttle sensor? I agree it is odd that two components would fail simultaneously.

Dougflas on Thu August 06, 2015 3:25 PM User is offline

Unplug the compressor clutch. If the connector has 2 leads, then there is probably no ground at the compressor. One lead, then the compressor is ground. Run a lead from battery to clutch hot side, neg battery lead to either ground or the other connector connection. Engine off. The clutch should engage. If not ,problem is from connector to clutch coil. You should normally read 3 to 6 ohms on coil. If that is good, I would be looking at clutch gap as mention before in this thread.

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