A/C compressor help

Just checking the A/C and it was a no go, Went to top off the r-134 and noticed the compressor wasn't running even after I added some Refrigerant. Checked all the fuses, both in the dash and under the hood and the relay, still no A/C.

Any thoughts?

Some of the controls in them years will shut down from low freon.
Any flashing lights on it?
Try a battery disconnect and see if it will reset and kick in.
If not.
Then go to low pressure switch and see if it is getting 12 volts to it and threw it.
If 12 volts to it jumper it and see if compressor will turn on.
If no voltage to it the controls is not turning Ac clutch on.

Some of the controls in them years will shut down from low freon.
Any flashing lights on it?
Try a battery disconnect and see if it will reset and kick in.
If not.
Then go to low pressure switch and see if it is getting 12 volts to it and threw it.
If 12 volts to it jumper it and see if compressor will turn on.
If no voltage to it the controls is not turning Ac clutch on.

No lights.

Will try battery disconect.

Low pressure switch location?


How to check through it?

The low pressure 2 wire switch is on the reciever dryer the big aluminum can on the right side firewall.
With engine running and AC turned on it should have 12 volts to the low pressure switch.
Just use a 12 volt test light or volt/ohm meter and check for 12 volts to it on one wire and 12 volts on the other wire going to compressor.
If you have 30 or more lbs of pressure or gas in system voltage goes threw the switch to run compressor.
Also check the wires at the switch plug in and connection there.

Hold up on them instructions unless you are working on the 1992.
If you are working on the 99 blazer or sububran.
Post back which one and if auto AC or manual controls.
Check all fuses. There may be more than one for AC.
But the low pressure on the 1999's may be a ground circuit instead of 12 volt power feed.
Sorry about the confusing on it.
MT

MT, I also have trubble with my AC. It's a 95 blazer V6 with simple AC system (no ACC, don't know it it was avalible then...)
Problem is that it does not engage the compressor. It started as a intermitent problem but now it does not run at all. Might be as simple as it need to be filled...

My question is: What are the electric connections of the AC system? Have not found a diagram of it yet...
There is the switch in the dash, the low pres. switch you described in this thread, clutch... what else??

Regards,
Freddy

Auto matic AC is on newer ones.
The 1995 power to ac clutch starts at ac control module.
Light green wire go to low pressure switch.
Check for 12 volt light green wire to low pressures switch with key on engine on and ac on.
From low switch it goes to AC relay white wire.
AC Relay is powered by gauge fuse.
From ac relay dark blue goes to high pressure switch.
From high pressure switch on dark green wire to compressor clutch.
Most common problem is low freon/R-134a.
If pressure is low the low pressure switch shuts off.
First check is for voltage to and threw low pressure switch.
Also check plug in and wiring at the switch.
You can jumper the two wires at low pressure switch for a test.
If compressor runs with it jumped there the problem is there.
Low freon/R134a or bad switch or wiring.
If system is low on gas do not go for them one hose one gauge one can stop leak crap killer kits at wal-mart or some parts places.
Get a ac low and high side gauge set and do it right.
MT

99 blazer with the computer control climate controls.

Low pressure switch has 13 volts to it.

The wires to the compressor have 0 volts. Sounds like the problem, but what will fix it?

I check both fuses in the dash and the 2 under the hood and the relay, all were in good shape.

Low pressure switch has 13 volts to it.

The wires to the compressor have 0 volts. Sounds like the problem, but what will fix it?

I check both fuses in the dash and the 2 under the hood and the relay, all were in good shape.

Sorry about the year mix up.
The 99 auto ac is a little different.
The low pressure switch is a ground circuit.
The dark green wire to is grounds the VCM.
It may show 12-13 volts on volt ohm/meter unplugged.
But will have to be grounded for the compressor to kick in
Jumper the switch and it should show no voltage or grounded there.
If system is low on gas under 30 lbs the switch will shut off ground circuit.
The black and white wire on one side of it is a ground wire.
The compressor clutch relay is feed power from ac on controls threw the High side pressure switch.
And the clutch is controlled by the VCM and ac module.
Check your private E mail for a wiring diagram.
Good luck and let us know how it goes.
MT

Compressor ran with the jumper installed on the low pressure wires.

I added 26 OZ of freon and couldn't get the pressure above 25 into the blue of the guage. No idea why it wouldn't run when the plug is hooked up, when I have been low before, as soon as I add freon the compressor would kick on.

The air is 40* F coming out of the vents.

Low side pressure needs to be 28 lbs or more for the switch to turn on.
What is the low side pressure with compress off?
It sounds like system is still low or has a bad leak.
Does the compressor turn on when ac is first turned on?
You need to get a low and high side reading with a ac recharging gauge with engine idle and engine at 2K with compressor running.

Low side pressure needs to be 28 lbs or more for the switch to turn on.
What is the low side pressure with compress off?
It sounds like system is still low or has a bad leak.
Does the compressor turn on when ac is first turned on?
You need to get a low and high side reading with a ac recharging gauge with engine idle and engine at 2K with compressor running.

Compress off, I just went out and put the guage on, in the yellow almost 65. I check my suburban and work truck and they were about the same.

Nope, doesn't turn on at all.

I guess it's time for the professionals.

If the low side has 65 compressor.
Check or replace the low side switch.
Ohm it out across the switch prongs.
It should have connection at 28-30lbs or more.

But on the other side if you have been having to add R-134a often it may be time to have it checked for leaks.
Good luck MT

I'll OHM it tonight.


Are you saying that if the low side has 65 when the compressor is off, it's a bad compressor?

What OHM reading should I get on the switch.

Do I have to drain the system to replace the switch?

I'll OHM it tonight.


Are you saying that if the low side has 65 when the compressor is off, it's a bad compressor?

What OHM reading should I get on the switch.

Do I have to drain the system to replace the switch?


No on the 65 low side comp off.

But the low side switch should be making contact threw it or show OHM"s reading for contact with 65 lbs.
The low side switch turns off or opens contact at around 28 lbs or lower.
Over 28 lbs it makes contact and under 28 lbs it opens up/no contact.

The switch will just screw off and on. No drain No problem changing it.

On the 200 OHM setting I got reading of .3 OHMS.

On the 200 OHM setting I got reading of .3 OHMS.

The switch is not turn on or making contact.
Try another switch.
MT

The switch is not turn on or making contact.
Try another switch.
MT


Will Do.

BTW, where can I get one?

GM parts dealer or you auto parts place will have them.

picked a few up at the recycling yard, and a few worked, so I started fooling around with some taking OHM readings and they were all about the same. So I replaced the original one and the A/C was working, if I played with the it. Guess it must have been a clog or loose connection.

Anyone need a sensor, I have several, ytellow, black and brown.

Glad you got it working.
They do have some wiring problems at the plug in on the switch.
If it gives you any more problems try a different plug in wiring.
Good Luck
MT

Hi, me again.

My low press switch act like it does not work so I thought I screw it out and check it, but it started bubbling at it when I tried to unscrew it.
As MT say "No drain" I like to know if mine is different then laxman's?
Can someone post a photo of it? I'll try to post one myself soon...

/Freddy


The switch will just screw off and on. No drain No problem changing it.

Hi, me again.

My low press switch act like it does not work so I thought I screw it out and check it, but it started bubbling at it when I tried to unscrew it.
As MT say "No drain" I like to know if mine is different then laxman's?
Can someone post a photo of it? I'll try to post one myself soon...

/Freddy

It is normal for it to lose a little bit of gas when you unscrew or install it.
But better to start a new thread/post on yours and give year and all info on what it is doing or not doing.
MT