Ford Ranger AC problem

[John-P]

Hi and low side pressures are fine. Cools very well. After a bit of driving on a hot day it just stops cooling all together. New relay, Cleaned electrical connections at pressure switches and clutch. It will usually come back on eventually and then do it again. Did it again today 3 times in a 24 mile trip. Still off as I pulled in the driveway. Got gauges and checked pressures. All normal for it if the ac was turned off. Motor running, ac on and nothing. Cooled condenser and radiator with water hose. Still nothing. True to form, it eventually came back on about 10 min latter. Any clues?

 

[NutBucket]

Is the evaporator freezing up?

 

[boomerang]

Your compressor is dropping out. The clue is that with it on, you check pressures and as you said, the pressures reflect the compressor not being engaged.

NutBucket could be right although pressures would not be OK.
Could be a flaky high pressure switch or low pressure switch.
Could be a flaky relay.
Could be a flaky compressor clutch.
Could be a flaky control unit (the interface in the dash.)

What year is this? Modern cars have diagnostic capabilities with the proper diagnostic tool connected. Nobody here is going to be able to tell you with certainty what the problem is because there are too many possibilities. Unless this is a known problem for x year and x miles, etc.

Did this problem come on suddenly, or after some work, either related or not related to the A/C system being performed?

 

[John-P]

Your compressor is dropping out. The clue is that with it on, you check pressures and as you said, the pressures reflect the compressor not being engaged.

NutBucket could be right although pressures would not be OK.
Could be a flaky high pressure switch or low pressure switch.
Could be a flaky relay.
Could be a flaky compressor clutch.
Could be a flaky control unit (the interface in the dash.)

What year is this? Modern cars have diagnostic capabilities with the proper diagnostic tool connected. Nobody here is going to be able to tell you with certainty what the problem is because there are too many possibilities. Unless this is a known problem for x year and x miles, etc.

Did this problem come on suddenly, or after some work, either related or not related to the A/C system being performed?

2002 Ford Ranger XLT

I can manually set the compressor off and it cools. Replace the relay and nothing happened. High and low side within range when running. blows and cools very well when it works.

 

[John-P]

Is the evaporator freezing up?

No

 

[Pacfanweb]

I agree with the compressor stopping.

Most likely it is the field coil, or magnet.

Easy to check. Get a test light. Wait until it quits again. See if the compressor clutch is spinning. Test power at the compressor. (should make the light come on)

If you have power at the field coil wire, take a screwdriver or something and kind of smack the clutch (assuming it's not spinning) into the pulley and see if it engages and starts running...or at least "clicks" some, even if it quits again.

That's an indication you have a bad field coil behind the pulley. Usually you buy the coil/pulley/clutch all together. Easy fix.

Now a relay can cause the same thing. It's not your evaporator freezing up, that'd take forever to melt and start working again.

 

[Zenmervolt]

I can manually set the compressor off and it cools. Replace the relay and nothing happened. High and low side within range when running. blows and cools very well when it works.

Honestly, given that everything works fine when you jumper the relay and directly apply power to the compressor clutch I would start out by replacing the relay. Should be relatively cheap and easy to swap out and it's a very likely culprit given what you've told us here.

ZV

 

[master_shake_]

http://www.wilsonautoelectric.com/tsb_database.html

take a look at the wiring diagram for your truck.

it shows the high and low pressure switches in series to a ground then in to the pcm.

when the switch opens the pcm shuts the ground off for the relay.

you're going to have to test for power at the power side of the ac clutch relay.

if you have no power you're going to have to start testing the high and low pressure switches.

if you had a gauge set it could be easier to diagnose.

 

[John-P]

Thanks for the link to the wiring diagram. I have a dual gauge set and vacuum pump from the R12 days with new 134a hoses and connections. As I understand the hi low pressure switches, circuit is closed under proper pressure. My suspicion is a sticking hi pressure switch when the switch is opened. Tapping on it made no deference when the ac stops cooling. The connection is at such angel you cant get a probe on the terminals when you remove the connection.

 

[John-P]

Is the evaporator freezing up?

Honestly, given that everything works fine when you jumper the relay and directly apply power to the compressor clutch I would start out by replacing the relay. Should be relatively cheap and easy to swap out and it's a very likely culprit given what you've told us here.

ZV

Tried new relay and still nothing until it gets good and ready in its own time.

 

[Pacfanweb]

How are you "manually setting the compressor off"?

 

[John-P]

By directly applying power to it.

 

[LTC8K6]

IIRC, there is a correct gap for that clutch to work properly?

If it stops working, rap it with a screwdriver handle. If that makes it start, the gap may be too wide?

 

[master_shake_]

have you tested for 12 volts on the relays power and control side?

then after that when it shuts off check for 12 volts going from the relay to the field coil?

if there isn't ground the control side of the relay and it should kick on.

if it does you'll need a scan tool to see if ac is requested from the heater control head on the pcm.

if it is and the ac is not working it may be one of the high or low pressure switches.

easy to check, use a dvom with the switch disconnected on both terminals the resistance should be ~0 ohms. engine off after it stops working.

check both switches that way.

if everything is good and still not working suspect the pcm.

 

[Pacfanweb]

IIRC, there is a correct gap for that clutch to work properly?

If it stops working, rap it with a screwdriver handle. If that makes it start, the gap may be too wide?

Yep, that's why I told him to try that.

Can't remember the gap...maybe around .030"?

Anyway, he needs to check for power to the compressor when it fails. If it has power, then it's the field coil and you just replace the assembly. If it doesn't have power, you work backwards, starting with the relay.

 

[John-P]

Ok, I think I have it narrowed down. It happened today. I tapped the clutch with a pair of pliers and it stuck to the clutch plate Got Magnetism. After another wack or two it finally kicked in and started working. So now, how to adjust the gap? or replace the plate. And can this be done without removing the compressor?

 

[NutBucket]

Good work detective. Hopefully someone can help with that procedure as I am not familiar with it.

 

[Pacfanweb]

To change the gap, you remove the bolt in the center of the compressor. I think it's 8mm. Work the clutch off, and there (probably) will be little shims behind it. Basically, they're small washers.
At the Ford dealership, we used to have different thickness washers so we could adjust the gap. It was trial-and-error...you just kept changing/or stacking the washers until you arrived at the correct gap.

Honestly, you should just go buy a new clutch/pulley/field coil assembly rather than mess with the gap. Less than a hundred bucks.

Shims: I took a pic of some old ones I have

 

[John-P]

Called all over town. no one had the hub or hub shims. So i figured, what the hell. Removed hub. Only had one shim in it. The gap before removal was 46. the gap after removing the only shim it had is 19. Ran all over town and it never missed a beat. Thanks to all for your help on this. Saved me a bundle $$$.

 

[Pacfanweb]

Called all over town. no one had the hub or hub shims. So i figured, what the hell. Removed hub. Only had one shim in it. The gap before removal was 46. the gap after removing the only shim it had is 19. Ran all over town and it never missed a beat. Thanks to all for your help on this. Saved me a bundle $$$.

Good news. I'd roll with it until it quits, then put and assembly on it. Easy job. One bolt and a pair of snap ring pliers.

 

[boomerang]

Called all over town. no one had the hub or hub shims. So i figured, what the hell. Removed hub. Only had one shim in it. The gap before removal was 46. the gap after removing the only shim it had is 19. Ran all over town and it never missed a beat. Thanks to all for your help on this. Saved me a bundle $$$.

That's cool! Thanks for keeping us in the loop. :thumbsup: