A/c wont work. Seems like ive tried everything!

[azfirebird]

In my 1994 Ford F150 5.0, my a/c started blowing hot and the clutch stopped engaging. Below is everything I have tried to diagnose this problem:

1. I tried putting more R134 in the low side, but the system wont suck any in. Maybe because the clutch won't engage???
2. I jumped the clutch directly to the battery and the clutch will engage just fine.
3. I checked for voltage at the clutch connector. I am getting 11.58 volts so I know the clutch is getting power.
4. Ive tested both high and low pressure switches and both are good.
5. Since there is no AC relay in this year truck, I checked the only AC clutch 15A fuse and the fuse is just fine. Ive tried jumping the connector at the low pressure switch. Still nothing.

I am at a loss. The air blows but just blows hot. Anyone have any other suggestions?? Please help.

Thanks

[jyount]

IF you have power at the clutch itself there is no need to jump stuff. Your clutch should be engaging and is not. If it has power the clutch itself has to be suspect... Ohm check the power wire to ground and repost. Disconnect the power connector first.

[azfirebird]

Jyount, THanks for your wuick response. I wasnt feeling very good yesterday so I couldnt get to my ac problem. Please forgive my naiviness but can you walk me through how exactly I am suppose to OHM check the power wire? Thanks for your help.

[azfirebird]

Jyount, THanks for your quick response. I wasnt feeling very good yesterday so I couldnt get to my ac problem. Please forgive my naiviness but can you walk me through how exactly I am suppose to OHM check the power wire? Thanks for your help.

[jyount]

Originally Posted by azfirebird

Jyount, THanks for your quick response. I wasnt feeling very good yesterday so I couldnt get to my ac problem. Please forgive my naiviness but can you walk me through how exactly I am suppose to OHM check the power wire? Thanks for your help.

FIRST, you have to have an ohmmeter. Most digital volt ohm meters have this. Other than that you will have to have an ohm gauge. Disconnect the connector at the clutch itself and check the clutch power to ground and between the two terminals if it has two. Don't remember how that one is set up. If it is any less than 1 ohm to ground OR too itself it is shorted. If it say 0.L, that means open line, means the wires are broke inside the clutch. It would behoove you to google some ohm stuff or some basic electrical and see some videos on the topic.

[azfirebird]

Thanks for the reply and the instructions. I checked the items you mentioned. Here are my readings:

Clutch connector *power to ground: 198.4 ohms

Across the clutch terminals: 3.9 ohms*

I'm so lost in why the clutch won't kick on. I don't understand why I am getting 12.5 volts through the connector but yet the clutch won't engage but it engages when I run 12 volts directly to the clutch and the cabin gets nice and cold.

[jyount]

Originally Posted by azfirebird

Thanks for the reply and the instructions. I checked the items you mentioned. Here are my readings:

Clutch connector *power to ground: 198.4 ohms

Across the clutch terminals: 3.9 ohms*

I'm so lost in why the clutch won't kick on. I don't understand why I am getting 12.5 volts through the connector but yet the clutch won't engage but it engages when I run 12 volts directly to the clutch and the cabin gets nice and cold.

You said it, 12.5 volts, then jump it to power and it works great...

It is called single wire syndrome for slang. Check your wires to the clutch of the fuse or something in the line to it. The best way to explain it to me is this - say you have a wire that has 40 smaller strands inside it. Say 39 of them are broken, only 1 strand is working, so straight voltage you will get full voltage, but it won't carry any amps. This is what you have, now just have to figure out why....

Laymans terms: Say you have a 1/4" pipe 20 foot long, and a 1" pipe 20 foot long. If you put 20 psi water through them they will both have the same 20 psi if you deadhead them and put a gauge on them. Now open the ends of said pipe and FLOW water through them, the 1" pipe will flow a ton more gallons per minute. Same theory, only you can see water. Electric seems like magic to diagnose because you can't see it...

[Jeff Collision]

May be your gas is on low. At idle you might have 25 psi pressure on the low side of the compressor and the compressor will run and kick in and out, you need about 45 psi to run good. When you run down the road, the motor speed and compressor speed is greater and it sucks the pressure down below 25 psi, switch kicks out, and compressor probably not running much if at all so it gets hot. You need to add more gas.

[jyount]

Hadn't thought of that, hard to work on stuff that isn't in front of you. If he was jumping the switch it still should engage though.

[azfirebird]

Thanks for your replies. I might have found the issue or might not have. Ok I evacuated my system and applied direct power to engage the clutch to recharge the system to spec. I then plugged the connector back into te clutch and jumped the high side pressure switch and viola the clutch engages and the air gets nice and cold. Does that mean the high pressure switch is bad?

[jyount]

Do you actually "have" high pressures? If you recharged it you should've had gauges on it, what are your pressures running?

[azfirebird]

Right now my readings are:

Low Pressure Side: 40 psi
High Pressure Side: 230 psi

I replaced the switch and it started working like a charm!!

[FNA]

jyount your posts seem quite helpful.

The following is merely for joking.

"Most digital volt ohm meters have this" (An ohm meter)

Most? I thought all volt ohm meters had volt meters and ohm meters, hence the name. If you have purchased an ohm meter without an ohm meter, you should ask for your money back.

[jyount]

Glad you got it fixed!

As for the funny, lol. I know that, just that a whole bunch of guys buy a meter and use it like a test light.....