AC works then later will not enage the clutch

[Ecomike]

I need to find out why my AC runs for a good while, then cuts out (too cold, normal) and will not activate the clutch later when it gets hot again unless I goose the engine to about 3000 rpm. Had that problem with the 89 ( may she RIP) and my 87 waggy for years now. I think I am going to try and debug that this month. Pretty sure it is/was not a Renix ground issue. The clutch and AC works fine when I first start the jeep.

I guess it could be something in the dash controls or the Evaporator thermostat going bad???

But why does the clutch always engage when I rev it to 3000-3500 rpm when it had suddenly decided it wants the rest of the day's trip off LOL. There must be a connection. The air gap on the clutch comes to mind, or voltage to the clutch (I think there is a diode in that circuit???) , but why does it work for a good while, always works on a fresh start up, then goes south after a 30 minute drive in hot weather? And why would a rapid rpm run up always fix it for a while until it gets a little too cold again in the cabin?

 

[Bobbie]

Ac regulater gone south.Cheap fix and you lose no fluid.Simple screw it off ,it has a valve like a tire rim.

 

[Ecomike]

Ac regulater gone south.Cheap fix and you lose no fluid.Simple screw it off ,it has a valve like a tire rim.

"Ac regulater"

Do you mean the low pressure safety switch on the filter dryer? I think this problem started when they were new, so I kinda doubt that is it. and it is the same problem on an 87 and 89, that both have new ones.

I agree they are cheap and easy to replace and would be the first part to suspect, but they tend to go bad completely in my experience and not repair themselves overnight. I will put that on the list and I can test it with an ohm meter on the side of the road the next time it happens!!!! In fact I can test the clutch voltage at idle and at 3500 rpm when it does it again.

However the evaporator thermostat that is intended to keep the evaporator-expansion valve from freezing is 30 years old.

But answer me this, why would a sudden ramp up to 3500pm fix the switch 100% of the time?

 

[Bobbie]

Yes ac low pressure switch .They are made cheap these days out of plastic

 

[kastein]

I seriously doubt it is the low pressure switch but since you have multiple vehicles maybe swap it to another to see which one acts up after.

This feels like clutch air gap to me but I could easily be wrong. You have an mt2500 right? Plug in and see if the ecu is commanding ac but not getting it, then you can work down the chain from there with a meter. You can configure any of the 4 LEDs on the mt2500 to indicate ac command status so it is easier to watch while driving, btw.

 

[Ecomike]

This feels like clutch air gap to me but I could easily be wrong. You have an mt2500 right? Plug in and see if the ecu is commanding ac but not getting it, then you can work down the chain from there with a meter. You can configure any of the 4 LEDs on the mt2500 to indicate ac command status so it is easier to watch while driving, btw.

Awesome, I had not yet figured out what the 4 LEDs were for on the MT-2500 LOL. I just bought the 3, 1" thick manuals off ebay, time to read them!!!

I was thinking air gap too, (but checking for other ideas too) as I adjusted the air gap on both rigs that have the same issue along time ago, and it solved the original problem to some extent. Maybe they get hot while running the first gig, then the gap grows when hot (the three thin metal fingers?) and does not want to engage on the second on cycle, but I was not sure the higher rpms would be related to fixing a marginal air gap!!!! I am now thinking they are!!!! Thanks!!!!

 

[kastein]

My guess is that the airgap is excessive and only once the alt output comes up to max at high rpm does it have enough grunt to pull in. But again, I am spitballing here.

I'll have to go play with my 88 and remember how to enable the LEDs. I just figured it out while recharging the ac on my wife's 93 roadmaster last night with r152a after doing a full system replacement. Was looking for a way to have the mt2500 force ac command on, but found that instead.

Edit: iirc it is somewhere in a menu you bring up from the live data screen, can't remember if it is the y or n button you push.

I seriously doubt it is the pressure switch since it wouldn't see anything different pressure wise till the compressor kicks on.

 

[md21722]

My guess is that the airgap is excessive and only once the alt output comes up to max at high rpm does it have enough grunt to pull in. But again, I am spitballing here.

I'll have to go play with my 88 and remember how to enable the LEDs. I just figured it out while recharging the ac on my wife's 93 roadmaster last night with r152a after doing a full system replacement. Was looking for a way to have the mt2500 force ac command on, but found that instead.

Edit: iirc it is somewhere in a menu you bring up from the live data screen, can't remember if it is the y or n button you push.

I seriously doubt it is the pressure switch since it wouldn't see anything different pressure wise till the compressor kicks on.

Yes, re-shim the clutch or replace the compressor. Of course you can check voltage to the clutch to make sure the system is commanding it on. It probably is, and the clutch is worn, the air gap is out of spec, and so the clutch is failing to engage the compressor. This starts off as "unexplainable" intermittent A/C operation followed by more rants as to why you are sweating in the heat and humidity while the gauges back at the shop show the system is working fine. If the clutch is worn out of spec the compressor may not be that far behind, and given what clutches cost, it may be more reasonable to simply replace the compressor if this is the problem.

Edit: I am not as familiar with the dinosaur Jeeps, so there could be extra sensors that are not working worth a darn. As long as the system is not icing up (visual inspection) I would think its the clutch. I had a Subaru that had an evap temperature sensor and there was a TSB to move it from one position of the evap to another. In that case the system was icing up which resulted in reduced air flow. The solution was to move the sensor. It was great driving through Houston in the summer time with this problem.

 

[90xj06]

atleast the renix era jeeps had a temperature sensor on the evaporator that would cut out the ac clutch when it got to ~40 and then once it warmed back up it would re-enable the clutch. it also has a low pressure switch too. but it doesn't sound like its that.

the only time the ecu cuts the clutch is if you go WOT.

 

[kastein]

BTW - if you end up having to open the AC piping to do repairs, PLEASE have the R12 recovered properly... there is only so much left in the world and it can't be produced legally anymore.

Also look at doing a conversion from R12 to R152a in that case. R152a is far less damaging to the atmosphere, far cheaper, and performs just as well, you just have to flush as much of the old mineral oil out of the system as you can and replace it with ester oil. I just did the conversion like I said in my last post, will report back if it performs as I hope it will.

 

[my2monkeys]

On my 89 I find that the clutch plates need straightening and the debris cleaned off once in awhile.
My compressor would act the same way as yours when coated with grime.

I have found that these Sanden units are bullet proof.

My original unit has 526,000 miles and still going strong.

Thats after going to r134a and back to r12 now.

 

[Ecomike]

Thanks I will clean the grime off of mine. I checked the voltage and the contacts, and I do have a voltage drop on mine, with no load:shiver: or 1 volt.

Cleaned the clutch connector, it was in need or cleaning (and also dropping the voltage at the clutch coil), next will work on the clutch relay and contacts where I seem to be loosing a volt as well, and my Bat_Alt voltage is only 14.01 volts, with no loads. IIRC it should be 14.7 volts. So I am missing almost 2 volts at the clutch. And it could use a little cleaning. I think It is already working better but I also used an old trick of bending the face plate fingers some with a screwdriver to tighten up the air gap. It helps for 1-2 years in a pinch LOL.

What is interesting is the run up of the rpm had no effect on the clutch voltage, it held rock steady at 13.0 volts from 750 rpm to over 3000 rpm.

It maybe a little slop in the clutch bearing, makes the air gap change at higher rpm that makes it kick in.

Mine runs fine with R-134a as I Installed the R-134a expansion valve, filter dryer and the 1997 Crossflow AC condenser (and a new compressor with 134a seals) IIRC about 10 years ago. It makes a huge difference!!!

On my 89 I find that the clutch plates need straightening and the debris cleaned off once in awhile.
My compressor would act the same way as yours when coated with grime.

I have found that these Sanden units are bullet proof.

My original unit has 526,000 miles and still going strong.

Thats after going to r134a and back to r12 now.

 

[Ecomike]

Any idea what the OEM air gap spec was on these beasts?

BTW - if you end up having to open the AC piping to do repairs, PLEASE have the R12 recovered properly... there is only so much left in the world and it can't be produced legally anymore.

Also look at doing a conversion from R12 to R152a in that case. R152a is far less damaging to the atmosphere, far cheaper, and performs just as well, you just have to flush as much of the old mineral oil out of the system as you can and replace it with ester oil. I just did the conversion like I said in my last post, will report back if it performs as I hope it will.

 

[Saudade]

Any idea what the OEM air gap spec was on these beasts?

I could not find a spec in my 88 FSM. I did find one in a 93. It said:

Using feeler gauge, measure air gap between clutch plate and pulley surface. Proper clearance is .013-.025" (.33-.64 mm).

Adjust shim thickness to obtain correct clearance. Tighten compressor shaft nut to 13 ft. lbs. (18 N.m).

 

[old_man]

My thoughts are that you are on the edge of having the right amount of "Freon" and after it warms up the pressure changes a bit and then it won't work.

 

[Ecomike]

I could not find a spec in my 88 FSM. I did find one in a 93. It said:

Using feeler gauge, measure air gap between clutch plate and pulley surface. Proper clearance is .013-.025" (.33-.64 mm).

Adjust shim thickness to obtain correct clearance. Tighten compressor shaft nut to 13 ft. lbs. (18 N.m).

THANKS!!!!! I think we have a winner here if the 87 is about the same, as I think my air gap is about 4-5 times that spec LOL. Mine is probably about 1.0-1.5 mm :laugh3: I must have a good clutch LOL

 

[Ecomike]

My thoughts are that you are on the edge of having the right amount of "Freon" and after it warms up the pressure changes a bit and then it won't work.

That was my thought but its been doing this for years in both rigs. I think they both had way too much air gap on the new compressors and I did not check them against the OEM spec when I installed them. And they worked so,.....I never gave it anymore thought.

I will know soon enough which it is.

 

[Bryan C.]

I have used a relay with direct to battery power source to power up the a/c clutch in the past for similar issues. Just use the OEM a/c clutch signal to actuate the relay.

 

[Ecomike]

The Renix jeeps already do that as far as a I know? I think my 1 volt drop is the relay internals and the dirty male-female pin contacts. I will checking that out.

I have used a relay with direct to battery power source to power up the a/c clutch in the past for similar issues. Just use the OEM a/c clutch signal to actuate the relay.

 

[kastein]

Yeah, I usually just use a chunk of wire, probe the connector and the battery positive with it and see if it kicks in. You don't want to run like that for any significant period of time obviously since that removes every low pressure and high pressure safety interlock from the clutch actuation circuitry, but it's good as a clutch test.