A/C works when driving but not at idle

BC

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Make
Toyota
Model
Sienna
Year
2013
Miles
100K
Engine
V-6
2011 Toyota Sienna V-6

A/C works when driving, but not when idling as in stopped or in park or at a red light. Once you start to rev up motor some, it engages. Any thoughts?

Thanks,

I accidentally posted this in domestic and couldn't figure out how to delete. So my apologies.
 

billr

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Do you want me to delete the other thread for you?

My guess is this is related to either the TPS or ECT sensor. Do you have live-data available?
 

BC

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I have a BAFX scanner that hooks up to my phone via torque app.
 

billr

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Look to see what the ECT and TP are at idle, when the A/C won't come on. And, look to see if the A/C is being "commanded" on.
 

BC

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Ok I'll check those tomorrow. Thanks!
 

BC

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So the ECT seems to be working. AC command is on. After running for about 15 minutes I notice the TP went from running relatively flat to what you see in the other photo. After revving it up a few times, it would go back to flat line and then in about a minute or two it would start the fluctuation.
 

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billr

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"Once you start to rev up motor some, it engages "

By "engages, do you mean the compressor clutch engages and the compressor begins rotating? That's what I assumed, but just checking...

Can you clarify what that graph means? The vertical scale doesn't make sense to me. One graph tops out at 22.0, the other at 36.0 Those don't seem like valid values for TP %, ADC counts, or millivolts; so I'm confused.

Regardless, if the A/C is being constantly commanded on, yet the compressor clutch disengages at idle, the TP and all other sensors are not the problem. What is the system (battery) voltage at idle, versus off-idle? That should also be in live-data, but confirm with a meter.

If battery voltage is OK, then check voltage at the connector to the compressor clutch, back-probing so the load is still on the circuit. If voltage goes low, or to zero, there, then I would try swapping the A/C relay for a similar one. Still no Joy? Then check voltages at the relay socket. That can tell you whether the problem is in the relay/compressor power circuit, or the PCM/relay control circuit; cut the search in half.

I think you are going to find that the relay is opening up at idle, either battery voltage is dropping lower than normal, or the relay is bad and can't tolerate normal lowering of voltage at idle.

PS: If you don't have a relay to swap, the appropriate power contacts in the socket can be jumpered for testing, but I don't recommend doing that. It is too easy to damage the contacts by jamming in a jumper that is too big. The voltmeter can tell you what you need to know.
 

BC

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Yelp, that was it! Battery was weak, alt check good. This van for a handicap friend and it had an interstate battery which look to be approximately 7 months old, but now these days that doesn't mean anything. Bought yota battery from dealer today and installed, working like a champ. Thanks for the info in helping with this! Much appreciated!
 

billr

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I question whether the alt is really "good". The alt should be able to provide plenty of power/voltage even at idle. Yes, there are some battery problems (shorted cells) that can suck down a good alt, but that would not be what I would call a "weak" battery. Probably would not even attain or hold a full charge voltage.
 
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