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04 ac diagnostic needed

11K views 8 replies 8 participants last post by  cmoore 
#1 ·
my 04 sienna ac stopped working (120k miles). it intermittently worked for a couple of days and now, nothing. it even seemed to stay on one time when i turned it off (button off with fan still on). the compressor does not seem to engage. i added a bottle of refrigerant a month ago because it did not seem to be getting as cold as it should. is it a relay, clutch, compressor or a whole system that needs replacing. how do i tell (i can and am willing to do all but the last one)
 
#2 ·
Sounds like a leak to me. It it professionally charged with a tracer die and go from there. Without a proper R134a level the system will not come on.

Regards, JC.
 
#3 ·
Check the sight glass near the fill port to see if anything is "passing through" there with the AC on. As previously stated, the compressor will not come on without R134a in the system. It will make a bit of noise as the system fills (garage thought that the compressor was trashed), but that can be considered normal. You could buy a can of refrigerant and do a DIY fill, although you will not want to overfill the system. I do not recall the capacity of the system, but a small can will not completely fill it and if the sight glass shows no movement you should be OK. The most common site for AC leakage is at the rear tire well, where the lines are most exposed to the weather. Our 2004 took a can a season and did fine, although this can be a pain over time.
 
#4 ·
You need at bare minimum a can with an integral gauge to see if there is pressure present on the low side. A proper gauge set is of course more accurate, but the can unit will at least give you an indication. If you don't have sufficient charge, the low pressure switch will inhibit the compressor from running. If you overfill it, again, the high pressure switch will inhibit the clutch from running, although damage to the system can still occur even with this safety device in place.

You said that once the system seemed to run even when the dash control was off. Are you sure the compressor was actually running then? If so, you might have a bad relay (marked MG CLT for magnetic clutch). It might be usually sticking open, but that one time stuck closed.
 
#6 ·
Ours didn't work one year, I put a can in it and it worked for a day. Then it did not work again, tried another can and heard a slight hissing noise coming from the condenser. Looked at the condenser and saw some Freon coming out from one of the fins. A tiny rock pierced one of the fins and caused a leak. If i used the Freon with uv in it I could have found the leak the first time with a black light.
 
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