Check the fuse and relay?

 

Thanks echo. Sorry, should have mentioned that: yes, I've checked the 10A fuses under the hood and in the inside fuse box. Both look good and measure accurately. But, I haven't checked any relays. I'm not aware of anything else that is not working so I figured relays were good.

 

Check and made sure the relay is getting signal to turn on and the output is getting power to engage the compressor clutch!
Also, there might be more than one pressure switch on some system, so check for that as well!

 

Is the 'HTR' relay the one to check? I don't have a wiring diagram. Thanks again.

 

All Wiring Diagrams for Toyota T100 SR5 1996 model – Wiring diagrams for cars

AIR CONDITIONING A/C Wiring Diagram for Toyota T100 SR5 1996List of elements for A/C Wiring Diagram for Toyota T100 SR5 1996:(2.7l a/t) (2.7l m/t)(3.4l a/t) (3.4l m/t)1994 vftc c2.7l A/c amplifier (right side of i/p)A/c dual pressure switch (right side of i/p)A/c fuse 10aA/c idle-up valve (rear...

portal-diagnostov.com

 

Which AC switch did you replace? The one in the dash that turns the AC on/off?

 

The one on the dash that you press in to turn on the AC and you depress again to turn off the AC.

 

Check for power to the clutch! If that is getting power then you may have a bad clutch or poor ground connection!
If the clutch is not getting power, check the dual pressure switch in the heater box, if that is open, the compressor clutch won't work either!

 

Thanks again echo. I'll check the power tonight. I was also thinking ground--any idea where the ground connection is for the clutch? I replaced the dual pressure switch and will double check the connections there but since this was a problem before I swapped the parts, I'm thinking the new switch is ok.

 

Can said for sure where the ground is, sometimes they just grounded to the compressor itself. If you have a two wire connector at the compressor, just use a test light to see if you are getting a good ground at the other wire; the black/white is the feed!

 

Check if you have power on clutch coil wire when a/c is on and engine runs. Should be single connector on top of compressor

 

Put 12v to the compressor and once you add another can of refrigerant the pressure switch will be out of the equation and things should be back to normal. Capacity is 22.92 oz, +/-1.76 oz.

 

Thanks sdspeed. I thought of that but was gun-shy about putting in another can--I figured one can was sufficient to kick off the compressor. I'll start with the power check. If there's no power, I'll go that route.

 

With one can your below 50%, I crawled under my T100, shouldn't be too tuff to get power to it, mine is so damn disgusting under there I didn't do much more than look. But when I was in a shop it was SOP if the pressure switch was a pain to get to.

 

Update: no power to the clutch. I put 12V to the compressor, it engaged and I was able to charge the system with the second can. But, still no power to the clutch. Hmm.

 

Check the dual pressure switch, should have power at blue/red wire when the AC is on, same for the red/green wire if the switch contacts are closed.
If those are good, check to see if the signal is getting to the AC amplifier. And if the AC amp is sending power to the clutch via the black/white wire.

 

it could be there is too much pressure, was it filled with gauges?

 

Yes, I filled with gauges. If anything, I think I'm probably a little low as the spec calls for 2 cans (22.92 oz, +/-1.76 oz) and I don't think I got a full 2 cans worth in the system. The pressure definitely went up by adding the second can but still no power to the clutch. I'll check the power to the pressure switch, amplifier, and then out based on echo's suggestions...probably a weekend activity. But, I'll report back with my findings.

 

one can should have brough it to the minimum of 5 lbs for the low pressure sensor. depends on the size of the a/c system.

 

At this point it's not a refrigerant issue if your hi & lo gauge readings were on target if you could have continued to let the system run and stabilize. Just went thru this on my MR2 (nightmare) and it ended up being the amplifier.
A/C amplifier or pressure switch.

 

OP indicated the system had 60 psi on both hi and low side; that should have satisfied the pressure requirements to engage the clutch!
Also leaning towards the AC amplifier; however, until the results of the inputs and output are in, don't want to say yay or nay.
At the same time, the AC thermister should also be checked to make sure that it is not shorted; if it shows no or low resistance, which translates as evaporator freezing, the amplifier will inhibit compressor operation.

 

Call a good AC mechanic shop and save yourself from months of guessing. Been there, done that.

I let an AC shop fix up my AC. The evaporator core and the part inside the car between the driver and passenger require a ton of dismantling.

After wasting much time and money I now have 'like new" AC for well over a year. Cost was $1200 including new compressor.

OEM AC parts start to fail after ten years - IME. I have a 2005 runner I purchased new for $40,000+. The AC began failing after ten years.

 

Is there an idle sensor - when A/C is on the idle needs to come up several hundred RPM to overcome compressor drag? Just brainstorming.

 

OP sounds capable of doing what needs to be done, why send the vehicle to somewhere else! Part of the joy of being a DIYer is the ability to take care of issues yourself!

If the AC amplifier is doing its job, it would have send signal to the ecu to activate the idle up. That is why the results are needed to see if the amplifier is doing its job!

 

I’ve seen a clutch not engage fro low pressure and also on some compressors there are shims on the clutch plate that can be adjusted, maybe the gap is too large, with engine running and A/C on, and you see the clutch not spinning, being real careful, using a large rounded tool as to not catch on the clutch as it may start spinning, put some pressure on the face of the clutch, if your gap is wrong it may give just enough to make it engage.

 

Hi again folks: just came in from checking a few things. I have power at the dual pressure switch on both wires. When I plug the harness into the amplifier, I'm not seeing any power on the black/white wire which goes to the compressor (harness contact #7). When I check power coming into the harness, I see the battery voltage at contact 4 when the AC switch is on and it goes away when I turn the switch off. In my mind, that is telling me the voltage is coming into the harness and never coming out of the amplifier.

I did some of the other checks from the FSM and wanted to run those by the group here before I replace the amplifier. Here is what I found when I measure the wiring harness while it is not plugged into the amplifier:

Test Connection	Specified condition	My finding
8-Ground	Continuity	80 Ω
2-6	Continuity	1280 Ω
4-Ground	Battery positive voltage with AC switch on	Tests good
4-Ground	No voltage with AC switch off	Tests good
7-Ground	Continuity with AC switch on	715 Ω
7-Ground	No continuity with AC switch off	490 Ω

Thanks in advance for your thoughts and ideas. Happy to get a replacement amplifier if all signs are pointing to that but if something doesn't seem right with what I've found, I'd sure love someone's thoughts on other things to check.

Thanks again.

 

Bumping to see if anyone has ideas on whether something other than the AC amplifier could be causing the problem or if this is strong evidence that the amplifier is toast. Thanks again.

 

Hi folks: an update but unfortunately not what I was hoping to report. I replaced the amplifier but no change. So, I'm back to what I assume is a ground or wiring problem. The airbag light is steady on: are there any common denominators between the SRS wiring and the AC? Thanks again for thoughts....