Jake_the_Snake

iTrader: (5)

First, i realize this probably belongs in the maintenance section, but i trust you guys more, so here we go.

my ac blows hot air, doesnt drip condensation, and the low side lines are hot. the compressor does not turn on. ,i jumped the low side pressure switch, the fans turned on and i could hear the car idle a bit higher, but the compressor clutch did not engage. instead, it threw a code, which turned out to be a TPS. wtf??

now, as far as i can tell, the ac was working the day before i changed out my pcm(sent to me by Ion), but was not the day after. ive checked all the fuses and relays and everything seems fine. is it possible he sent me a bad pcm?

if not, anybody know a good ac shop in the fort worth/mid cities area?

1SLwLS1

iTrader: (6)

Try jumping a hot wire straight from the battery to the compressor and see if the clutch engages.

If possible, try swapping back PCM as well. The PCM controls the A/C Relay. http://www.ls1lt1.com/forum/showthread.php?t=10894

Jake_the_Snake

iTrader: (5)

thanks, i'll have to try that

TheBlurLS1

iTrader: (8)

There are tables in the PCM that control the A/C clutch engaging and disengaging. They are based on RPM and TPS. You can put a volt meter on the A/C plug and see if it's getting signal to come on when commanded.

PS - I just noticed that you've got an LT1 car. It may have something similar, but I'm not sure.

Jake_the_Snake

iTrader: (5)

ok, i tested the ac relay and it seems im not getting power to pin 86(or 85, i cant remember). either way it looks like its not getting signal from the computer to switch from open to closed. just for ***** and giggles i jumped a lead from pin 87 to the battery and sure enough the clutch engaged. so now im pretty sure its the computer, unless anybody has any other ideas? ive already checked both fuses and ive swapped the ac relay with 3 other ones and still nothing.

1SLwLS1

iTrader: (6)

85 is the incoming trigger source for the solenoid/coil, 86 is outgoing ground from 85, 87 goes to whatever you are powering, and that power comes from 30, usually your main buss. SO, if you are not getting 12 Volts from the computer, it will never work.

Another test would be to supply 12 volts from the battery, low amperage of course. Do this, connect a short wire from 30 to the 30 terminal on the fuse box, another short wire for 87 to 87 on the fuse box, and one final short wire from 86 to 86 on the fuse box. Then leave 85 disconnected. Nothing should happen at this moment. Then take power for a relatively low amperage, 12 volt source and connect it to 85 on the relay ONLY. Do not send 12 V back to the computer via the connection on the fuse box. Just send it to the relay. This will tell you if your relay works controlling the ac clutch. Although this may be unnecessary, as you have tested 3 other relays, they could all be bad. Those little delicate things are thrown around in boxes as they are shipped to here or there, and the little solenoid/coil inside, contrary to belief, is very fragile.

There are also other ways to test relays, just ground the 86, send a known power to 30, trigger the solenoid to force the circuit close via 85, and test if 87 is getting power.

If all that fails and all of your relays are fried, try jumping connections 30 and 87 on the fuse box to see if the clutch engages. The paper clip won't last long due to the relatively low resistance and high amperage, but it should be able to tell you if those connections are still valid.

1SLwLS1

iTrader: (6)

Just for your reference, incase you did not know...

http://www.miata.net/garage/images/h...ng_diagram.gif

Jake_the_Snake

iTrader: (5)

oh, when i say i tested the relay, i mean i tested the fuse block, so the slots for 85 and 30 were getting power. i jumped slot 87 and the clutch worked. so i guess i'll try jumping 30 to 87 to see if that works

1SLwLS1

iTrader: (6)

you jumped 87 with what? 12V from the battery or something?

Jake_the_Snake

iTrader: (5)

yeah just jumped it from the battery, which caused the clutch to engage with the car off. i jumped it from 30 which initially did nothing, but with the car running and the ac switched on, the clutch engaged.

1SLwLS1

iTrader: (6)

OK, yea then your terminals are good. The paper clip from 30 to 87 just lets you know if you are still getting power from your main buss. Try the whole short wire connection from 86, 30, and 87, and power from the battery to 85(Relay only!) and see if it engages, that will eliminate everything but the computer!

Jake_the_Snake

iTrader: (5)

will do. ive already asked Ion if he knows what else it could be, and without further question, said it's probably the pcm and has another one on its way with prepaid shipping on my current one. talk about awesome customer service, Ion Rules!

1SLwLS1

iTrader: (6)

sounds good man, let me know how it turns out for you. I am in the process of diagnosing my g/f's 2000 Silverado. She doesn't have consistent AC, but I never have any time to actually work on it, so she is sweating it up in the Houston weather, lol.

THE SHOP

Boils down to what was changed from when it was working to now, to be honest if this went out on its own though you would have several things to check beside pcm, high side, lowside switch, compressor relay, reference signal, freon etc.