A/C Cluth rapid cycling cause?

[helosailor]

Just like the title says. The freon (checking on the low side) is at the correct pressure and replacing the A/C relay made no difference.
When driving, every 5-10 seconds the clutch will engage with a pretty loud chirp, stay engaged for 5-10 seconds then repeat. The A/C does blow fairly cold.

Any ideas of other causes? I guess worst case scenario would be a bad clutch and/or compressor.

This is on a 1994 Isuzu Rodeo V-6, btw.

Thanks for any insight.

[stephen4785]

Over charged, under charged, or a bad cycling switch.

[helosailor]

Thanks for replying Stephen, I was hoping you would.
If I measure the pressure on the low side and it is right on, is that accurate enough? Also, where is the cycling switch? On the clutch?

[CJ]

Sounds like an under charge to me.

[BP]

Those trucks also use an evaporator temp sensor to switch the compressor on and off.

I'd check the voltage at the clutch and see if it's staying constant, if so then I'd look at a clutch problem. Most of the time they they either work or they don't, they won't pulsate.

If the voltage is fluctuating the easy thing to do would be to switch the relay with one of the other ones and see if it makes any difference. If no difference then it could be one of the two pressure switches or the temp switch. You should be able to just jumper the leads in the connector and see which one makes a difference. If none of them make a difference then it could either be PCM related or possibly the a/c controller.

This is all assuming there isn't actually a freezing evaporator and the pressures are within specs btw.

[Chili]

Thanks for replying Stephen, I was hoping you would.
If I measure the pressure on the low side and it is right on, is that accurate enough? Also, where is the cycling switch? On the clutch?

Hey, I have manifold guages at the house, if you want to stop by Saturday some time we can hook it up and get the pressures for high and low sides. Not that I can help diagnose but knowing those numbers may help other diagnose without seeing it themselves..

[garycrist]

I vote low charge (SWAG).

[helosailor]

Sounds like an under charge to me.

The charge when reading from the low side is good. It was 50 psi @ 82* when I checked it.

Those trucks also use an evaporator temp sensor to switch the compressor on and off.

I'd check the voltage at the clutch and see if it's staying constant, if so then I'd look at a clutch problem. Most of the time they they either work or they don't, they won't pulsate.

If the voltage is fluctuating the easy thing to do would be to switch the relay with one of the other ones and see if it makes any difference. If no difference then it could be one of the two pressure switches or the temp switch. You should be able to just jumper the leads in the connector and see which one makes a difference. If none of them make a difference then it could either be PCM related or possibly the a/c controller.

This is all assuming there isn't actually a freezing evaporator and the pressures are within specs btw.

Crikey! That might be a little above my paygrade. I'll check what I can though.

Hey, I have manifold guages at the house, if you want to stop by Saturday some time we can hook it up and get the pressures for high and low sides. Not that I can help diagnose but knowing those numbers may help other diagnose without seeing it themselves..

Thanks Craig! I have one I'm going to hook up now...if I can find it. If not, I'll definitely take you up on that.

I vote low charge (SWAG).

See above


Thanks for the replies guys. I'm trying to figure out what it isn't first, starting with the cheapest stuff. I have a nagging feeling that it's going to get expensive though.

[1fast4]

Different vehicle, but my Mark VIII was throwing same code/issue. It was a slow leak in one of the hoses. Had hose repaired and system refilled with no issues since. Been over 2 months since repaired.

Hope that helps any?

[JimD]

Suction side a little high, you add any freon?

[helosailor]

Different vehicle, but my Mark VIII was throwing same code/issue. It was a slow leak in one of the hoses. Had hose repaired and system refilled with no issues since. Been over 2 months since repaired.

Hope that helps any?

I'm hoping it's not that. In fact, I'm fairly sure.

Suction side a little high, you add any freon?

Ok, here's the crazy thing. I checked it the other morning (when it was 82*) and it was 35 psi and the chart showed it should be between 50-55 psi. So, I added some freon, enough to get it to 50 psi. Now, I just came in from checking it again (at 105* this time) and it was 65 psi, but the chart shows it should still be 50-55 psi. So, I bled it down to 55 psi. Now, the clutch doesn't rapid cycle at idle any more, but as soon as I rev it it starts rapid cycling. I also noticed that the window on the receiver/drier is cloudy. Could that have something to do with it?

[CJ]

I'm hoping it's not that. In fact, I'm fairly sure.

Ok, here's the crazy thing. I checked it the other morning (when it was 82*) and it was 35 psi and the chart showed it should be between 50-55 psi. So, I added some freon, enough to get it to 50 psi. Now, I just came in from checking it again (at 105* this time) and it was 65 psi, but the chart shows it should still be 50-55 psi. So, I bled it down to 55 psi. Now, the clutch doesn't rapid cycle at idle any more, but as soon as I rev it it starts rapid cycling. I also noticed that the window on the receiver/drier is cloudy. Could that have something to do with it?

pressures will increase with ambient temperature.

[helosailor]

pressures will increase with ambient temperature.

Oh, I know. I thought it odd that the temp/pressure chart would have the same pressure listed for 80* as 105*. I figured there was some sort of pressure regulation that went on. I'm really pretty dumb when it comes to a/c systems. Now if it was a straight up pneumatic system, no problem.

[CJ]

Oh, I know. I thought it odd that the temp/pressure chart would have the same pressure listed for 80* as 105*. I figured there was some sort of pressure regulation that went on. I'm really pretty dumb when it comes to a/c systems. Now if it was a straight up pneumatic system, no problem.

If it was void of refrigerant before you started this, then it clearly has a leak. I was never a fan of the stop leak shit, but a friend of mine that owns an AC shop says it works and doesn't damage any components, so you might look into that for a cheap fix.

[helosailor]

I'll keep that in mind. I think I'm just going to take it over to a guy I've dealt with several times in Haltom City. He's always been quick, honest, and fair. I'll have him check it over and tell me what's going on with it. At this point, I'm kind of afraid that if I jack around with it any more, I might really mess something up.