compressor not getting power to turn on

[seth556]

Well it's now summer and I'm desperately needing cold air in my truck. Problem is the a/c compressor isn't coming on.

I've checked the pressures, fuse, relay, and given the compressor 12v directly and it came on. So the problem is that something is stopping it from giving it 12v when I turn on the a/c so it engages.

What is a common part to break that would cause this? And how would I check to see if it's that part?

 

[ranger7ltr]

You have narrowed the problem down to the source...

Since the clutch engages when direct power is applied to it the problem is, most likely, lack of refrigerant charge sufficient to close the low pressure switch on the accumulator...

I would put your gauges on the system and see what readings you get...If the charge level is high enough then you might have a defective low pressure switch...You can easily replace it by removing it from the accumulator and screwing a new one on in its place...You can test the switch to see if it is causing the non start problem by jumpering across the 2 contacts...I would caution only jumpering long enough to see if that is the problem of no power to the compressor clutch...

If the charge level is low though, that would need to be brought back up to have the system turn on when you turn the a/c controls on...This switch stops the compressor clutch from engaging when the refrigerant level is too low...Since the only way to lubricate the compressor is by moving refrigerant and the oil suspended in it, if the charge level is low, the compressor would not be lubricated if the system is operated without enough oil flowing through it...

Commonly a leak will show itself as a dirty area on a hose or at a fitting/connecction as oil will also come out as well as refrigerant...And if you have a leak you should fix it to avoid this type of problem or worse in the future...

Let us know what you find...

 

[seth556]

I tried jumping the leads that connect to the low pressure switch (on top of the accumulator) and nothing happened. So apparently that isn't the problem...

 

[ranger7ltr]

This is sounding like a lack of voltage...

When you checked the a/c relay, did it click when you turned the a/c on or did you swap it with another relay? Do you have voltage coming to the relay? Do you have voltage coming to the a/c fuse?

The first thing I would verify is these 2 items... Then I would look at the a/c control switch to see if there is voltage coming to and through it when turned on...

And, of course, make sure all connections are made at the accumulator and the compressor...

 

[seth556]

I just checked the relay by switching it out, I'll see if it clicks though. And I'll check the fuse.

 

[seth556]

There wasn't a click when I turned the AC on. And I checked the voltage of the fuse and it was about 4v although I was using a AAA battery as ground because I couldn't find any place within reach to use as ground.


EDIT: Checked the relay again and power is only coming from the signal wire. So I'm not sure if the low pressure switch or anything else would stop power coming to the relay through the signal wire or the high amp hot wire (whatever the name is). I rigged 12v from the relay next to it and the compressor came on. So the problem would be something is causing the hot wire connection not to have power coming to it.

Is there always power going to it when the car is on? And would the low pressure switch trip that or the signal wire? If it trips the signal wire and not the hot wire I can rig a new 12v connection to the relay.