AC mystery

I've got a condition that's been happening on and off for a couple of months now. Seems like when it's really hot, the compressor doesn't engage normally. When it happens, normal driving for about ten minutes usually causes it to kick in and when it does cold air is there immediately. I can see that the compessor is not turning when yjere is no cold, so it's not a door issue. No way to know when it will happen, but it's usually when it's real hot. Once engaged, it stays engaged until I shut it off with CCC or shut off the car.

Climate control center seems to work normally - can hear doors opening and closing as you go from cold to hot and back. The fact that it happens when it is really hot must be a clue there for someone that really knows these things.

One thing for sure - I can't take this not working - there's a ton of glass in these whales and Florida can get pretty hot.  When it's working it blows ice cold.

Replaced the pressure switch and it seemed to work for about 5 days. Today was really hot and it happened again

forgot to mention - 94 Roadmaster LT1 85K

When this happens check to see if you have power to the A/C clutch. If you have power at the clutch and no engagement more than likely the clutch coil is faulty. If there is no power, check the relay that controls the A/C clutch engagement. Of course there are many other possibilities but these seem the most problematic. Also, make sure the ground for the clutch coil is good.

Today was really hot and it happened again. This morning while it was cool, the clutch engaged the compressor on starting and immediate cold. At lunchtime (hot) , started car, no engagement of compressor, no cold.
Tonight (still warm), started car, no engagement, no cold.  Drove for about 15 minutes, suddenly engaged, immediately cold.

Is it possible that the amount of freon isn't right. And when it's hot, it expands and increases the pressure to the point that the pressure switch won't send power to the clutch until it cools down some ?

Maybe driving a few miles cools it down enough to allow electrical power to the clutch?

Thanks for any advice. I got to get this fixed. Or, I'll fry!

I know that the fill amount is dependent on ambient temp. Set the dial to the outside temp and fill to the "full" mark. Not sure why.....

roadmasterBlue wrote:

Today was really hot and it happened again. This morning while it was cool, the clutch engaged the compressor on starting and immediate cold. At lunchtime (hot) , started car, no engagement of compressor, no cold.
Tonight (still warm), started car, no engagement, no cold.  Drove for about 15 minutes, suddenly engaged, immediately cold.

Is it possible that the amount of freon isn't right. And when it's hot, it expands and increases the pressure to the point that the pressure switch won't send power to the clutch until it cools down some ?

Maybe driving a few miles cools it down enough to allow electrical power to the clutch?

Thanks for any advice. I got to get this fixed. Or, I'll fry!

Low pressure cycling switch typically opens around 25 psi to prevent evaporator freeze up on an CCOT system. High pressure cut-out switch (if equipped) typically opens around 400 psi to prevent excessive pressure buildup in the system. I really don't think you are experiencing either one of these conditions, but I've been wrong before. Don't rule out intermittent switch operation, cycling switch is inexpensive and easy to swap out without discharging the system. 

You say the system is cold when its working, therefore I think the charge is pretty close to were it needs to be. Quick test, grab the liquid line and suction line out of the evaporator, with the system operating, if they are equally cold the charge is real close to being ideal. 

I do believe you have a electrical issue. Here is a diagram of the electrical circuit that controls A/C clutch operation. Have fun.

There is another, strong, possibility: excessive clutch gap. The gap should be no greater than about the thickness of a folded business card. If the gap is too wide, the electromagnet will not pull it in to engage the compressor, even if everything electrical is perfect. And the problem is very often intermittent: facing uphill, a bump in the road, etc. may be just enough to engage it. Since metals expand when hot, this may be just enough to make the difference in your case.

The sure test is to tap on the front of the clutch with the engine running and the AC turned on, however THIS CAN BE DANGEROUS, USE EXTREME CAUTION!!! 

No shims are required on the RM. Resetting the gap can be done with the compressor installed using a clutch tool to adjust the position on the shaft.

Now it's really getting weird. First of all, the AC thing happened again today, only this time after driving for a little while, then shutting the car off, the blower for the AC continued to run. And, I couldn't shut it off. I checked the fuse box to see if I could pull a fuse to stop it. Where the fuse for AC/blower is shown in the diagram, there is no fuse already?

I had to disconnect the battery to stop the blower. Is my climate control all screwed up? As soon as the battery is connected the blower starts again.

Any ideas?

The tool is called a hub and clutch drive plate remover/installer. You need one sized for the HD6 compressor used on the RMW. There's 4 parts: a drive point, a centre bolt, a thrust bearing and an outside body. The outside body is threaded M22 x 1.5 on one end, M9 x 1.25 down through the centre axially and a smooth shaft on the other with a hex in the middle. The smooth shaft is sized to fit inside and against the thrust bearing. The centre bolt is threaded M9 x 1.25 and the drive point fits over the threaded end.

The clutch drive plate is a press fit on a keyed shaft. The clutch gap is adjusted by simply pushing the drive plate on further (to close the gap) or pulling it out (to open the gap).

To close up the gap, the drive point is removed and the centre bolt threaded into the compressor shaft. The thrust bearing is placed over the body and the body threaded down over the centre bolt until it contacts the face of the drive plate. Then hold the centre bolt still with one wrench while you tighten the body with another wrench, drawing the drive plate closer until the gap is about 0.020" to 0.030" (a folded business card is close enough).

For removing, the body is reversed, so the threads will engage the internal threads of the drive plate. The drive point is fitted to the end of the centre bolt. With the body threaded into the clutch drive plate, the body is held still with one wrench and the centre bolt is wound in so that the drive point presses against the shaft like a puller and the body draws the plate off the shaft.

Then the key falls out of the shaft and disappears into the dark abyss below, necessitating a snipe hunt with a flashlight for the next 30 minutes before you find it actually just stayed in the plate. Don't Ask Me How I Know This (tm).

The tool is called a hub and clutch drive plate remover/installer.

Would you happen to have the Kent Moore J number of the tool?  Thank you.

Well if you are simply made of money, go ahead and buy a J-33013-B from Kent Moore. But bear in mind that you can buy an entire Mastercool 91000-A kit for less than half the price (and of course then you can do just about any automotive AC compressor ever made). I understand that many auto parts stores will loan the tool if you put down a damage deposit. Or, you could fab up your own with a suitable hardened M9 bolt, nut and some washers.

why are you guys on to the clutch??  wtf?

it works,. it cools,. sometimes hot,. sometimes cold,.erratic,.

so obviously when its needed the clutch is working,..

Quote :

Replaced the pressure switch and it seemed to work for about 5 days.

think you need to stay focused,.inmho it,s a connection somewhere that is sensitive to vibration or jarring,.check all plugs,clean all connections, and use dielectric grease,.

Nick

phantom 309 wrote:

why are you guys on to the clutch??  wtf?

Please re-read my initial foray into this discussion. As I said, excessive clutch gap can result in intermittent operation and is a very common problem with older clutches that have experienced wear over many years of use. Even facing uphill or downhill can make the difference when the clutch gap is excessive. It actually meets your definition of "a connection somewhere that is sensitive to vibration or jarring", even though a clutch is a mechanical connection.

It is very easy to check the gap. If the gap is OK, then move on to seeking an electrical cause. But if the gap is excessive you would only be wasting your time and money hunting an intermittent electrical issue that doesn't necessarily exist. Case in point: he already wasted money on a new low pressure switch.

Rule #1 of troubleshooting: Always investigate the simplest possible problems first because a) they don't take much time or money to check and b) they are usually the problem anyway.

Thank you for the info on the tool.

I swear someone had replied to my problem with the blower running after key is taken out yesterday with a response that it was most likely the blower control module. I even think another agreed with that opinion. Now I don't see those posts. Am I blind, or going crazy. Anyway, I ordered a new one (AC delco) and it will be here Thursday.

Of course this brings up a few more questions;

Does anyone know exactly where this thing is located? One of the reviews on amazon says its under the passenger side dash. I took a look just now, and it looks like there is all kind of electrical stuff there.  Based on the picture on amazon, it looks like I may have spotted it. It appears to be mounted so that is would appear to be aimed pretty much straight up into the middle of the glove box. It has three small bolts and two clip connectors. I'd say it's about 2x3" rectangular.

If I were to disconnect it now, would it be OK to run the car? Or should I just wait until I get the part?

Any chance this thing going bad could be related to my original Intermittent AC problem.                           

Thanks again for any advice you have. It looks like a pretty simple fix.

I do have another problem that maybe a few of you have figured a way around. At my age (54) I nee reading glasses to look at anything close. I get all my glasses at dollar stores and usually go for about a 1.5. Because of the location of this thing, I have to lay my head on the floor and look up.  This puts me so close to the subject, my focus isn't good, and it's difficult to see what I'm doing. I'm thinking I might       
have to buy a pair of more powerful readers (maybe something like 3.25) maybe I should get a pair with the led lights mounted on them because it's pretty dark down there.

put the 1.25's over the 2.50's,. 
result is manual bi-focals,..

works for me,.

buickwagon wrote:

Case in point: he already wasted money on a new low pressure switch.

Hmmm,. but it worked for 5 days,..?

Hokay,...nuff said from me.

yes i did post about the blower module,. and they can get water in them yada yada,..
but i deleted it,.

i,m no expert.

Nick

Got the blower control module today and put it in. Fit perfectly and solved the problem - no more fan running with the key out. 

Thanks for the advice on the module. 

AC worked great tonight. I think I'll drive it a few more days and see if the blower control module may have something to do with the problem. Seems like my fan blows harder now. Maybe the dying module was messing up the current flow. Maybe somehow messiing with voltage to the compressor.  Just guessing... I really don't know anything about this stuff, and the more I see, the more impressed I am with anyone that works on these modern cars. They sure are a lot more complicated than they used to be.