Air conditioner help

[mjdemaris]

Another problem just came up with my 1999 1500 suburban. When I press the AC button, the indicator light comes on, but no cold air.

I am searching for some schematics at the moment and thought I'd drop a post here for some expert advice.

I realized that the ac clutch does not engage at all when the button is pressed. Does this mean low refrigerant, bad relay or switches?

It all worked a few months ago, before I started fixing the random engine misfire problem. But I did not touch the AC components back then.

Also, read some info on using a scanner to find info on AC request. However, not sure if this scanner (MD9000) has that ability (it's a friend's).


Mike

[777stickman]

Check out this site for service manuals.

http://alldatadiy.com/

[Tech II]

here ya go:

[j cAT]

Originally Posted by mjdemaris

Another problem just came up with my 1999 1500 suburban. When I press the AC button, the indicator light comes on, but no cold air.

I am searching for some schematics at the moment and thought I'd drop a post here for some expert advice.

I realized that the ac clutch does not engage at all when the button is pressed. Does this mean low refrigerant, bad relay or switches?

It all worked a few months ago, before I started fixing the random engine misfire problem. But I did not touch the AC components back then.

Also, read some info on using a scanner to find info on AC request. However, not sure if this scanner (MD9000) has that ability (it's a friend's).


Mike

what you need is not a scan tool but a gauge set to measure the amount of pressure in the HVAC system. with little pressure the low pressure switch will not allow the ac compressor clutch to engage. this is to protect the compressor from lack of refrigerant and oil. if this is the case then I would add one 12 OZ can of refrigerant and see if it gets the ac compressor to run a little. then add another 12 OZ and I would also add some pag 150 refrigerant oil 2 OZ with a charge can to make sure you have a good amount of oil... old systems tend to lack the proper amount of oil. you can and should add some dye leak detector as well. that way you will see if you have a big leak that will need attention. working the engine you may have loosened the passenger side ac tubing/fittings causing a leak.

the use of gauges will reveal the problem in most cases. the system as I mentioned has this low pressure switch. this switch must have 5 psi or more of pressure at all times or the compressor clutch will not engage. so with a pressure reading and the engine on ac on if the pressure is above this 5 psi the compressor should be rotating..

now lets say the pressure is operating around the 40 psi or more . the ac is on . then using a jumper wire short out the low pressure switch located at the tank on the passenger side see if the compressor clutch engages.. then if this gets it running you must get a new low pressure switch .. these unscrew then install new. this switch when this old is worn out and this may be the reason.. true sometimes being cheap on testing equipment is stupid cheap.. this is when you will pay more to correct the problem [ guessing].. if you have a major ac failure then having an ac shop make repairs is a smarter way to go... this would be like as was mentioned the compressor belly is wet with oil... this does occur and if so a new compressor is best at this age ....ac shop would be required...

the use of charged cans of 134 and the proper oil [pag 150] and dye leak detector is available at most stores.. with a charge kit this can be installed easy...

the system uses / the spec of oil is about 8-9 OZ... after many years the addition of 2 OZ of oil , replaces the oil that leaked out.

with proper pressures and the ac low pressure switch working/good and you still have no clutch engagement this then may be a ac control or the clutch coil including the gap of this clutch ..

check all fuses and connections to these ac under hood devices then can get corroded etc..

make sure the belt is good and the tension is correct..

[brcidd]

Suburban - number one cause of a/c failure- loss of refrigerant- number one leak location- compressor belly....is it oily?

[mjdemaris]

Stickman, thanks, but I'm trying to spend as little as possible.

TechII, thanks, it looks like those are the same ones I found. Thinking I should check the clutch, and relay.

j Cat, I opened the port on the low pressure line, and gas came out. This tells me there is freon in there, but not how much. Going to call O'Reilly's and see if they rent ac gauges. And, you are saying 2oz of oil per 12oz of freon? Where do I get dye and the equipment to check it? Probably auto store...

brcidd, from what I can see, I don't see any oily/dirty areas under the compressor. The condensor(?) at the front of the vehicle does not appear to be damaged without taking it apart. There is a canister on the passenger side, near the firewall that has a couple of lines attached, and there is some, not a lot, of "oily grime" around two of the fittings.

Also, is there a way to determine if the clutch is the problem? Should I be able to hear the relay click if all else is good? On the other hand, if the system pressure is too low, then the relay should not engage, right?

Mike

[mjdemaris]

brcidd, your firebird, are you going to fix that gasket? Seems like that is a car worth keeping.

Mike

[777stickman]

Originally Posted by mjdemaris

Stickman, thanks, but I'm trying to spend as little as possible. Mike

Aren't we all. Although sometimes spending as little as possible ends up costing more. For $28 it could very well be worth it.

Good luck to you.

[brcidd]

Cycling switch on accumulator needs 47 psi to kick on compressor- so is system pressure that or better?

[mjdemaris]

Well, I checked the pressure as best I could with a can from the parts store. Had to jumper the pressure switch connector to get clutch to engage. The pressure started at about 55, and gradually kept going down to about 48-50, before I turned off the engine. I don't know how long I can run it jumpered.

At this point, I haven't checked the fuses, etc, but I am thinking that it might be the pressure switch (which is located on the side of the evaporator).

I did notice some grime around the switch itself. Also, after running the AC with pressure switch bypassed, after I turned off the engine, I heard a hissing sound as if gas was leaking out or some sort of overflow mechanism was opened.

Thoughts?
I am going to call the shop and see what they charge, otherwise I might be able to buy the proper gauges and refrigerant and do it myself.

[j cAT]

Originally Posted by mjdemaris

Well, I checked the pressure as best I could with a can from the parts store. Had to jumper the pressure switch connector to get clutch to engage. The pressure started at about 55, and gradually kept going down to about 48-50, before I turned off the engine. I don't know how long I can run it jumpered.

At this point, I haven't checked the fuses, etc, but I am thinking that it might be the pressure switch (which is located on the side of the evaporator).

I did notice some grime around the switch itself. Also, after running the AC with pressure switch bypassed, after I turned off the engine, I heard a hissing sound as if gas was leaking out or some sort of overflow mechanism was opened.

Thoughts?
I am going to call the shop and see what they charge, otherwise I might be able to buy the proper gauges and refrigerant and do it myself.

with the ac off / engine off the pressure at the low side test/charge port should be 110 psi approx.....If you have less than this you have very little refrigerant in this system. the ac may start for a sec.. then quickly shut off.

with no gauges you should not work this I recommend you have an experienced ac auto repair shop that does ac work often , check out your vehicle for leaks .. then put on vacuum pump check for leaks and re-charge the system adding some leak detector and a 2oz PAG oil charge for losses over the 15 years of use...

jumping the low pressure switch with little or no refrigerant will damage the ac compressor.

[Tech II]

To know what is exactly going on, you really need a set of gauges....not sure which switch you jumpered, the low pressure or the pressure cycling switch.....

The gauges on those cans sometimes are not accurate......If you jumpered a switch, and had the can on the low side, and the compressor ran, as the pressure dropped, you should have let the can stay open...the low side can go as low as 30psi......should also feel the low side line....it should get colder as the refrigerant flows into the system.......

Usually on the accumulator, there is a yellow tag, that states the capacity of the system......If your system was low on freon, and you added the can to the system, you will not get the entire contents of the can into the system, as the pressure in the can and the system tend to equalize....not sure what size can you are using......

The hissing sound, when the system shut off, was just the low side and high side equalizing....

Since some freon did go in, without the switch jumpered, turn on the vehicle and the a/c....if the compressor comes on, and shuts right off, or runs for a few seconds, and shuts off, you are still low on freon....

If you get gauges, with the system off, and the engine cold(first thing in the morning), hi and lo pressure will be equal, and should approximately be the ambient air.....so if the outside air is, 80F, pressure on both sides will be about 80 psi......when the compressor starts, the low side will drop to 30-35, and the high will go to 150-200, depending on load on the system, humidity, etc....if the low side drops too low, the pressure cycling switch will open and will turn off the compressor....as pressure equalizes, it will close and then the compressor runs again until pressure gets too low.....this is known as a cycling clutch, and is indicative of a low freon situation....

As the guys have said, the best situation is for pros to handle this....find the leak....fix the leak.....pull a vac on the system, and add the correct amount of refrigerant and oil to the system......

Those cans, are only good for "topping off" a system with a very small leak....

[mjdemaris]

Thanks for the help guys. I'll let you know what happens when I get it done.