AC Cutting Out-- Long (1 Viewer)

[sjpitts]

I am continuing to have AC troubles in my wifes 93 80-- with R134. When the problem originally ocurred, I evacuated and recharged the system. Unfortunatly, this utilimately did not solve the problem.

The problem is that the after running for a few minutes (and cooling quite nicely) the compressor just turns off. Interestingly, when we were in the White Mountains (relatively cool-- in the 70's) the AC would run great for almost thirty minutes before shutting off. In the valley of the sun (90-113 degrees) the compressor only runs for a couple of minutes before it shuts off. When you start the car up again (after it has been shut off for a while), it will again run for a few minutes before shutting off.

I put on my harbor freight guage set, and the pressure reading looks to be fine. Well, the high side is just a bit high (up to 250 PSI, versus 227 given as the top range in the FSM), but I don't think that it is high enough to be causing it to shut off. Plus, it is very hot here. The low side is in the FSM's range.

I borrowed an electronic leak detector and could not find any leaks.

I should note that it almost always shuts off when I slow down. For example, if I start it up and drive around it will run good for a few minutes and it will invariably shut off when I am coming to a stop somewhere- like I at the first red light I run into. You can feel it shut off because the incoming air instantly becomes real humid.

What do you think could be the problem?

Because it runs longer in cooler weather, and shuts off when you are slowing and the RPM's drop, my first guess was that it could be coolant temperature switch. The FSM says this switch is on the drivers side (US) of the engine block--above the oil filter-- but there appears to be two sensors sensors there, and I am not sure which one is the AC coolant sensor. The FSM gives a test procedure for the switch if I could just figure out where it is. Can anyone help me there?

I should say that a month or so before this problem started I flushed my cooling system, and replaced the radiator, fan clutch, thermostat and belts-- and I have never had any indication of overheating-- so I don't think it is an actual problem with the cooling system-- although I wonder if my alternator belts are looser than they should be-- I should check that just to be sure. And I guess in theory it could be a water pump problem, but you would think that a spike in temperature would be visible on the temp guage before the AC would shut of-- wouldn't you?

Stupid non-linear temp guage.

Other than the coolant temperature switch, I can't think of anything else that could be shutting of my ac compressor. Even though the pressure is a little high, the FSM says that the pressure switch cuts off at 450 PSI, and we are no where near that. Although in theory, that switch could also be bad.

Anyone else have any ideas as to what could be happening?

It was a 112 degrees yesterday, and no AC will soon begin to have negative impacts on the wife/husband relationship. Basically, really I need to get this fixed.

Thanks

Jared

 

[alaskacruiser]

You sure you're not overheating? Sounds suspiciously like it to me. The A/C cutting out is a classic symptom, and you can't always trust the temp guage to tell you when it is happening (I think around 226F is the A/C cutoff if memory serves and I'm pretty sure the temp guage doesn't move much past center at that point). Another thing that makes me think it is cooling system related is you say it happens when you slow down, which is when coolant temps rise. Check your cooling system .

 

[sjpitts]

You sure you're not overheating?

Well I guess I am not completely sure. Like I said, radiator, fan clutch and thermostat are all new, with OEM parts from CruiserDan. Fluid is new toyota red, mixed 50/50 with distilled water.

I don't think the temp guage has ever reached the half way mark.

I think it is possible that the alternator/water pump belts are a little loose. I Ebay'd a belt tension guage, but I have not yet figured out how to get it on that belt. I guess in theory the water pump could slip at low RPMs. Or maybe the water pump is just going bad-- but I don't really know how to test that.

But like I said--I don't think the temp guage has ever reached the half way mark. What is the normal point anyway?

OTOH, is it even conceivable that the car could reach 226 degrees within a couple of minutes of starting-- even when it is just sitting in the driveway--running at 1500 RPM (that is how you test the AC pressure). Starting from a cold engine, and running it at 1500 RPM the AC cuts out within a couple of minutes.

Could I put an ohm meter on the engine coolant temp guage sensor and measure it directly? Assuming I could find it-- like I said, I think the engine and AC sensors are side by side, and I don't know which is which.

Jared

 

[clownmidget]

Jared, what do you see in the inspection glass with the a/c on high under these conditions. I'd check that too. This also sounds a bit like an over-charged system. Also, is your a/c system holding the pressure? You can do the coolant hose squeeze trick to check and see if your water pump is properly circulating coolant but I don't imagine that's it as you'd hear it acting up most likely. I know mine behaved like this right after I bought it and it had just received a "certified Toyota dealership inspection and service". The a/c was grossly overcharged, the coolant looked like the factory original, and the front end needed the complete rebuild from inner seals out! But I did replace everything you just mentioned and had the a/c evacuated and then recharged by an a/c specialty shop here in southern CA where I got to watch. Now it works really well. Hope this helps and good luck.
Mike R.

 

[sjpitts]

Jared, what do you see in the inspection glass with the a/c on high under these conditions.
Mike R.

It looks good to me-- clear when it runs, bubbles when it turns off.

This also sounds a bit like an over-charged system.
Mike R.

It could be a tad--I filled it myself--see the thread on exploading R134-- but I don't think it is the problem. Like I said, with the system running, the Manifold guage set showed the pressure to only be at 250 PSI, nowhere near the 450 PSI where high pressure switch would cut if off. Plus, it wasn't rising when it cutt off, so I figured it couldn't be a rise in pressure that triggered the cut off.

Also, is your a/c system holding the pressure?
Mike R.

What do you mean?

You can do the coolant hose squeeze trick to check and see if your water pump is properly circulating coolant but I don't imagine that's it as you'd hear it acting up most likely.

Can you explain this test-- and what would it sound like acting up?

Thanks

Jared

 

[landtank]

It sounds like a coolant temp problem to me. Especially since iot runns longer when it's cool out. At 226 you would not see any difference in the temp guage as I had my system shut down to to temp in Death Valley and the guage looked normal. And yes the coolant temp can rise that fast at idle. Check for bubbles in your overflow tank.

 

[sjpitts]

At 226 you would not see any difference in the temp guage as I had my system shut down to to temp in Death Valley and the guage looked normal. And yes the coolant temp can rise that fast at idle.

Once again-- I hate the fact that we don't have a nice linear temp guage. Why did toyota do that to us? Can we fix it?

Check for bubbles in your overflow tank.

I know what you are insinuating, and I don't like it.

Otherwise, thanks

Jared

 

[clownmidget]

It looks good to me-- clear when it runs, bubbles when it turns off.

Yeah, I figured you had checked the obvious but...


It could be a tad--I filled it myself--see the thread on exploading R134-- but I don't think it is the problem. Like I said, with the system running, the Manifold guage set showed the pressure to only be at 250 PSI, nowhere near the 450 PSI where high pressure switch would cut if off. Plus, it wasn't rising when it cutt off, so I figured it couldn't be a rise in pressure that triggered the cut off.

ditto, proceed to coolant system/overheating...


What do you mean?

Just venturing a guess that maybe you lost your coolant due to slowly leaking system, etc.


Can you explain this test-- and what would it sound like acting up?

Thanks

Jared

Pilfered from a website describing the tech.
To check for a worn water pump seal, pressure test the system and watch for coolant leakage. Coolant will leak out of the small drain hole at the bottom of the pump or at the end of the pump shaft. Worn water pump bearings are checked by wiggling the fan or pump pulley up and down. If the pump shaft is loose in its housing, the pump bearings are badly worn. A stethoscope can also be used to listen for worn, noisy water pump bearings. Water pump action can be checked with a warm engine. Squeeze the top radiator hose while someone starts the engine. You should feel a pressure surge (hose swelling) if the pump is working. If not, pump shaft or impeller problems are indicated.

 

[Rich]

The factory service manual details the position of the temp sensors. There are three in a row on the left (US driver's) side of the block. In no particular order the sensors are the water temp gauge sensor, the "tell the computer the real temp" sensor, and the "shut off the AC over 226F" sensor.

 

[LandCruiserPhil]

Jared Why dont you jump the temp sensor and see if the problem exist.

Phil

 

[landtank]

Ok, there is 3 sensors in a row along the top of the block above the oil filter. The middle one is the cut sensor for the ac clutch. This is a normally open switch. Which means it closes when it reaches the designed temp. I'd unplug this switch and run the truck to see if the ac then runs correctly. If it does then that switch is definately cutting out the AC. Now the only thing left to do is to determine if the switch is triggering at too low a temp or if you have a cooling problem.

One might replace the temp switch with a new one to see if that helps. Or you could place the switch in an oil bath with a VOM attached set for continuity. While monitoring the temp of the oil with a thermometer start heating the oil. Eventually the oil will be hot enough to trigger the switch which you see on the VOM. Read the temp of the oil when that happens. If it's around 226 deg then your truck is overheating if not then it's the switch.

I personally would price out that switch and then decide which route to go.

 

[Photoman]

Another test you could try is tap your meter or test light into the positive wire on the compressor and see if it is still getting juice when the AC cuts out. This would test the compressor clutch. If it is getting weak it could be getting hot and cutting out on it's own.
Pic of sensors.

Bill

 

[Tools R Us]

Some Toyotas have a high compressor head pressure and/or a compressor temperature cut off switches, ether could cause your symptoms. Best to consult a FSM to understand how the system works.

 

[cruiserdan]

The 80 series does not have an RPM sensor in the compressor. There could be an issue with the high-pressure or low-pressure switches.

 

[Beowulf]

>> I think it is possible that the alternator/water pump belts are a little loose. <<

New OEM belts, properly tensioned would be the very first thing to do.

>> What is the normal point anyway? <<

Mine stays ~1 needle width below mid-point.

>> I hate the fact that we don't have a nice linear temp guage. Can we fix it? <<

I like Bill's solution so much that I am doing exactly what he did. Get a high quality temp guage (Greddy's are ~$180), an A-pillar pod, and put the temp probe in a new location somewhere in the cooling system. Details of Bill's solution are in the archives if that's the route you plan to take.

-B-

 

[lurker]

>> I think it is possible that the alternator/water pump belts are a little loose. <<

New OEM belts, properly tensioned would be the very first thing to do.

>> What is the normal point anyway? <<

Mine stays ~1 needle width below mid-point.

>> I hate the fact that we don't have a nice linear temp guage. Can we fix it? <<

I like Bill's solution so much that I am doing exactly what he did. Get a high quality temp guage (Greddy's are ~$180), an A-pillar pod, and put the temp probe in a new location somewhere in the cooling system. Details of Bill's solution are in the archives if that's the route you plan to take.

-B-

I hate to ask this, but where are the archives?

 

[sjpitts]

Ok, there is 3 sensors in a row along the top of the block above the oil filter. The middle one is the cut sensor for the ac clutch. This is a normally open switch. Which means it closes when it reaches the designed temp. I'd unplug this switch and run the truck to see if the ac then runs correctly. If it does then that switch is definately cutting out the AC. Now the only thing left to do is to determine if the switch is triggering at too low a temp or if you have a cooling problem.

This is exactly what I needed to know-- I couldn't find this info in the FSM, so I did not know which sensor was the AC sensor.

Thanks

Jared

 

[sjpitts]

OK, here is a general I recap. After reconsidering all the info last night I decided to take another look at the cooling system. I finally pulled out that belt tension guage and got it on the water pump belt. It was loose. So, I tightened it up using the guage. I had hopes that this would solve the problem but it didn't. Once again, the AC cut out within a few minutes of starting the truck.

I also took a good close look at the temp guage-- it appears to be running right the halfway mark. Based on what you guys have said, I think that could actually be running hot. You have no idea how much that guage bugs me.

I did the bubble check-- and couldn't see any bubbles in the tank. This made me feel a little better. I did squeeze test on the radiator hose and couldn't really tell anything. I am not sure what I am looking for here.

I think my next course of action will be to start it up and run the AC till it quits. I will then pull the AC temp sensor plug and see if the AC works again.

Like LandTank says, if it does then it will just be matter of trying to decide if the thing is actually heating up or if the AC sensor is bad. I would like to figure out a way to put an ohm meter on the sending unit (probably the guage, but maybe the computer) and getting an accurate temp reading that way. I think there is a chart in the FSM that gives the resistance as a function of temperature.

I have also given some thought to just premptively replacing the water pump. I live in Arizona, and have 112k miles-- a new water pump would probably be a good idea in any event. I should have just done it when I was replacing the radiator and fan clutch. I just need to find out what the CDAN price on a waterpump is.

One more thing-- the thermostat is new OEM-- replaced a month before this whole thing started. Have they been known to go bad in that timeframe and start restricting flow?

Jared

 

[Beowulf]

Jared,
The "archives" are old messages here on IH8MUD and, for the really old ones, you can get to Keep's SOR archive of the 80 section messages. (I don't have that link handy but it's easy to find with a SEARCH.) All you have to do is use the SEARCH button above and you can get to an Advanced search function. Put in "probe" and the author "Photoman" and you will get several relevant threads. I believe we've lost some good images but you'll get a lot of good ideas.

For example, read this thread for more information specific to your request.

I wouldn't suspect a bad thermostat based on your description of the A/C problem. I also don't suspect that your truck is overheating based on the information you've supplied. It's starting to sound like a bad sensor or wiring to the sensor.

If you had OBD-II you could get a precise reading of the temperature using a scan tool.

-B-

 

[Photoman]

Jared,

Here is a couple of charts that I ran in hot oil on the sensors if it helps you. Also, you may be thinking backwards by pulling the wires on the AC cutoff sensor (either that or I am since I have to go) I think it is a NC (normally closed) switch/sensor so pulling the wires is the same as it opening which it does to shut off the AC compressor anyway. In other words if you pull it you may want to jumper across the wires. FWIW, the gauge sensor has one wire, the other two have two wires connected.

Bill