2003 Ac compressor won't engage

Hey guys.
Need some help with a total a/c replacement.
Everything is in and I'm getting power to the compressor plug when I turn the ac on but it's just not engaging.

The compressor is new from rockauto.
The plug looks suspect. I would think it would need two prongs, not just one.
Is this the problem???

 

just a thought, the compressor only gets power when the engine is running by the relay in the under hood fuse box, just wanted to be sure you were aware of that.

touch 12v from battery positive to the plug (no need for engine to be running for this test) and you should hear the magnetic clutch engage, if not then the clutch is bad and you need to replace the clutch. if the clutch is working then its most likely the relay is bad.

 

The A/C clutch connector only has one conductor (+12v). The ground is thru the clutch body (horns are the same way). Are you saying that you have power to that one conductor (at the clutch) when the A/C is on?

 

With truck running and plug unplugged I checked power at truck side of plug when the ac button is pushed. When ac is selected on it shows power.

 

Ok. Ran wire from battery and can here the clutch engage.
I didn't think these trucks had relays only ac amplifiers.

Now I'm very confused because I can get power on truck side of plug when truck is on and I select the ac on.

 

I went check my 04 and you are right, we don't have the a/c relay in the fuse box but there is a 10 amp a/c fuse in there you should check.

main power for the a/c clutch must be switched through a relay because of the high current load so it may be switched in the heater control panel or the relay is inside the truck somewhere but wherever they put it, its most likely the relay switch that is bad or the wire between the plug and the switch so find the pressure switch, and put a jumper wire across the connection and see if that fixes it?

maybe the pressure switch contacts are bad. I don't see where it is, but every a/c system has a low pressure cut off switch the keep the compressor from running when it is low on Freon and burning it up. just follow the plug wire and it will go to this pressure switch wherever it is located at which is probably down there behind the compressor somewhere,

when you see 12v at the plug, all you are reading is 12v meaning things are touching but not that current can flow, the switch contacts are bad and not letting it pull any amps for power. its easy to get confused by this but just because you read 12v doesn't mean its a strong connection that will allow current to flow.

 

Thanks! That helps because I was pulling my hair out on seeing 12v and it not working.
I ran a hotwire from battery with truck on and got the compressor to engage and run.
I already jumped the pressure switch plug. No help. It has a high low combination switch I think.

That would suck if the pressure switch is bad and I have to evacuate the system again to replace it. I jumped that plug and that didn't do it though.

I also just ran a wire from truck side of comp plug to the comp plug and no luck.
I must not be getting power there
After all.

 

Ya think that means there was nothing wrong with your old system, since you have current flow issues?

 

Nah. I bought the truck a few years back with a frozen compressor and no belt on compressor. Just not sure what other issues there are with it.

 

Well that's good. Sounds like something I'd do! Buy an expensive item then come to find out it was the two dollar doohickey that was the problem....

 

Have you charged the system? compressor will not engage if refrigerant charge is low [low pressure cut switch].There is no way to charge system if compressor will no engage.

 

It has 100 psi static on the low side. When I jump the compressor it's showing about 25 psi on the low side.
If think that would be enough to at least cycle the compressor.

 

I am having the exact same problem. My compressor locked up so I replaced the compressor and the dryer. So... just to confirm, the compressor will NOT engage if the system charge is too low?

I was not having this problem before with the other compressor, and I checked my fuse just to be sure. I would assume I am not having any electrical problems.

 

no this is not a locked up compressor.

his clutch is not kicking in and when he tested the clutch, it works fine, so his problem is the clutch is not getting power even though its reading 12v but no current is flowing to power it meaning a switch or relay somewhere has bad contacts and needs replacing

 

Right, I got that... but "bubba bud" mentioned that a compressor clutch would not engage if there was not sufficient refrigerant charge pressure. I am wondering if that is the problem I am having.

 

well yes there needs to be pressure in the system before the clutch will engage. there is a switch on the back of the compressor that closes the switch only when the system has freon in it. it closes at around 40 lbs or so, so with the engine off, add one full can of Freon to the system first and that's enough to let it come on, then start the car turn on the a/c and add the rest it needs.

even with everything working fine, the clutch will not kick on unless the engine is running so keep that in mind as well.

 

Good deal, I am not very familiar with ac systems and I was concerned that my compressor was not turning after I hooked everything back up. I am having it vacuumed, purged and charged tomorrow so hopefully everything will work out.

Sorry OP didn't mean to thread jack. Thanks Keakar.

 

Keakar, have you worked on a Taco A/C system? Pretty much everything you've said so far applies to older vehicles but not the Taco. The pressure switch is actually in front of the evaporator core in the cab on the low pressure line. As someone else said, there is no relay for the A/C clutch, it is an amplifier circuit. But you are right, there is a minimum pressure that it needs to kick on.

I just rebuilt mine, only to find out my compressor has a blown front crank seal but nevertheless I have torn into and worked on it.

 

Update :

It turns out I should pay more attention to my volt meter settings.
I don't have power at the plug going into compressor just continuity.

I do have power and continuity at the following places :
10 amp fuse for ac
At the pressure switch
At the ac/heater control panel

I also have power coming from truck side of plug that goes into a thermistor that sits inside the evaporator housing. BUT I DONT have continuity coming out of the
plug coming from the thermistor?

Not sure how it works but I would think i should be able to test it for continuity.

Anyone know?

 

Did you ever find the problem with this? I'm stuck in the same situation right now.