'94 ETC Random A/C shutoff

[Ion]

Hi again. Its been a couple years of having no problems with my '94, but I just knew it wouldn't last! I'm once again having similar issues with my now 2+ year old MAP Sensor, which will be replaced again with genuine GM parts, but...the a/c randomly shuts down and sometimes fires right back up and other times, stays off for days. All connections are solid. I was hoping someone else has experienced this issue and might have some insight?

[KHE]

Is the A/C compressor clutch engaged when the system quits working or is the clutch disengaged?

Is there a low refrigerant code set?

[Cadillac Jim]

Anything that shuts down the A/C will throw a code, because this is done by the PCM which throws a code for any action it takes to solve a problem, and the code tells what the problem is. Examples of OBD DTC's that might be thrown in such a case:

P0526 Cooling Fan Speed Sensor Circuit

P0530 A/C Refrigerant Pressure Sensor Circuit Malfunction

P0531 A/C Refrigerant Pressure Sensor Circuit Range/Performance

P0532 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage

P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage

P0534 Air Conditioner Refrigerant Charge Loss

P0645 Air Conditioning (A/C) Clutch Relay Control Circuit

P0646 Air Conditioning (A/C) Clutch Relay Control Circuit

P0647 Air Conditioning (A/C) Clutch Relay Control Circuit

P1531 A/C Low Side Temperature Sensor Fault

P1532 A/C Evaporator Temp. Sens. Circuit Low Voltage

P1533 A/C Evaporator Temp. Sens. Circuit High Voltage

P1534 A/C High Side Temp. Sensor Low Voltage

P1535 A/C High Side Temperature Sensor Circuit

P1536 Engine Coolant Overtemperature - Air Conditioning (A/C) Disabled

P1537 A/C Request Circuit Low Voltage

P1538 A/C Request Circuit High Voltage

P1539 A/C Clutch Status Circuit High Voltage

P1540 Air Conditioning (A/C) Refrigerant Overpressure - Air Conditioning (A/C) Disabled

P1541 A/C High Side Over Temperature

P1542 A/C System High Pressure High Temperature

P1543 A/C System Performance

P1544 A/C Refrigerant Condition Very Low

P1545 Air Conditioning (A/C) Clutch Relay Control Circuit

P1546 A/C Clutch Status Circuit Low Voltage

P1547 A/C System Performance Degraded

P1548 A/C Recirculation Circuit

[Ion]

I'll have to go out and collect the codes and see if any are a/c related. I have a list of all codes I can reference.

[Cadillac Jim]

I just listed a bunch of codes to make the point that whatever is the problem very likely threw a code or two. The codes I listed are OBD II codes; your 1994 car will have OBD I codes which have a letter and three numbers, such as

B111 A/C High Side Temperature Circuit Problem

B112 A/C Low Side Temperature Circuit Problem [A/C Clutch]

Just a search for "A/C" on my OBD I code list has 16 hits, so it's very likely that anything that cuts off the A/C wil throw an OBD I code too. Be sure and keep track of any that are CURRENT, but list all the HISTORY codes too.

[Ion]

No a/c related codes generated. Only relevant codes are MAP sensor related (P032, 052 & 071).The 095 is the engine stall and 109 is one due to replacing battery. Now the motor seems to not be running on all cylinders (running choppy). This has never occured before. Can this be related to MAP sensor issues? Or...might this be due to running low on oil to the extent the PCM informed me to "check oil level"?

[airmike]

I seriously doubt the check oil level will effect performance. My daughter let hers get 4 qts low and it still ran fine. I think the indication comes on, one quart low, since it holds 8, no problems. I can't comment on the map sensor.

[Cadillac Jim]

The Check Oil Level message is presented when you still have four quarts of oil left, not counting the filter, and it's intended to warn the driver *before* the oil gets low enough to be a problem.

MAP codes will cause the PCM to go into an open-loop mode, in which the DFI works like a carburetor rather than using all the sensors to keep the mixture perfect for conditions. Normally you will see a loss of performance, gas mileage, and shift smoothness, but not rough running. If the engine is indeed missing, eventually you will get a P095. I don't see an OBD I code for an engine miss short of a stall. The P072 shows an erratic MAP signal that could cause rough running. I would check the connector to the MAP sensor and the wiring harness under the beauty cover and fix the problem that throws that code.

If you aren't getting any A/C-related codes, I would check the resistance of the A/C clutch, the connector, and the wiring harness near the A/C compressor.

[Ion]

The Check Oil Level message is presented when you still have four quarts of oil left, not counting the filter, and it's intended to warn the driver *before* the oil gets low enough to be a problem.

MAP codes will cause the PCM to go into an open-loop mode, in which the DFI works like a carburetor rather than using all the sensors to keep the mixture perfect for conditions. Normally you will see a loss of performance, gas mileage, and shift smoothness, but not rough running. If the engine is indeed missing, eventually you will get a P095. I don't see an OBD I code for an engine miss short of a stall. The P072 shows an erratic MAP signal that could cause rough running. I would check the connector to the MAP sensor and the wiring harness under the beauty cover and fix the problem that throws that code.

If you aren't getting any A/C-related codes, I would check the resistance of the A/C clutch, the connector, and the wiring harness near the A/C compressor.

There was an 095 present (listed in previous post). 2+ years ago, I was having MAP-related errors and by replacing it with a GM OEM MAP sensor, problem went away...until recently. Are these things known to go bad after less than 3 years? Or can oil flying around under the cover cause them to foul up? I am going to unscrew the cover, inspect the MAP's connections and level of cleanliness and connection, then see what happens. If no progress, I will order another GM MAP sensor. Can anyone tell me what causes these sensors to go bad or...produce the codes mine just did? For example, can a clogged O2 sensor cause MAP issues?

[Ion]

Oh, btw...to hell with the a/c issues, for now, I just want the engine to run properly!

[Cadillac Jim]

My 1997 ETC has the original MAP sensor. I got a MAP code some years ago and had it in my hand;it looked fine to me so I put it back and made sure the connector was clean and tight and never a peep since. Thus it's my opinion that the most likely cause of a MAP code is connector or wiring harness issues, particularly something like the P071 you reported, which is a "scratchy" connection - and that's more likely to happen at the connector than inside the sealed sensor.

The short story is that I don't hear about a lot of MAP sensors going bad, but I do hear about a lot of connector problems on sensors anywhere in the car, and I had a connector problem on my MAP sensor once.

In your first post, you said that your 1994 ETC had gone years with no problems. If it's been a lot of years and a lot of miles, there are other things that you might look at for a rough-running engine, particularly with a sudden onset of the problem. In particular, I'm thinking of plug wires. If the rough running started right after driving in a hard rain (through deep puddles) or after getting a car wash, particularly if the car was power-washed under the hood, that could bring out some ignition problems. Also, there's the possibility of water in the gas, if you bought gas at an unfamiliar location right when the problem started, etc.

[KHE]

Ion,

Refer to post #2 - When the A/C cuts out, is the compressor clutch engaged? This could be as simple as a clutch air gap adjustment.

[Ion]

KHE...I am not capable of determining if the compressor clutch is engaged when a/c cuts out. How does one do this when car is running and on the road? When it cuts out, I'm on the road, driving the car. Most of the time, it turns back on quickly on it's own. In fact, for the last few years, it routinely cuts out and starts back up frequently. It's become quite normal for me. Only a minority of the time does the a/c stay off for a long period of time. Regardless, my priority now lies in getting the car to run properly, due to MAP sensor issues. A new sensor is on order and have learned a new trick to prevent them from failing in the future. I found this tip on another Cadillac-related forum.

[Cadillac Jim]

Note that the A/C fan will continue to run but the air will slowly warm up of the A/C compressor drops out. If the fan is what it cutting out, you may have a bad connection to the fan motor or possibly a fan motor that is going bad. If the fan runs, but the air comes out the footwell instead of the A/C vents it could be the air mix doors. That should throw a code such as

B440 Air Mix Door Problem

A040 Air Mix Valve (Door) Circuit Problem

You can get an idea whether or not the A/C clutch is slipping by parking, letting the car idle, and watching the compressor. When the compressor engages, you will hear a click and the compressor will turn. When it is NOT engaged, the pulley will turn but the compressor will not. If it's slipping badly enough to see, the clutch probably will work OK with an air gap adjustment.

You know that the A/C is running if the fans run at low speed all the time, even when the engine is not hot and the temperature gauge is reading straight up. If you don't hear a click at all, then there is an electrical problem or the clutch is bad.

IIf the PCM is turning off the A/C compressor, the PCM or PZM will set a code such as

B112 A/C Low Side Temperature Circuit Problem [A/C Clutch]

P123 (E123) A/C refrigerant pressure was too low

P126 (E126) A/C high pressure switch disabled A/C compressor

P128 (E128) A/C was disabled because of high refrigerant pressure

[KHE]

You stated the A/C sometimes cuts off for days. My thought was to open the hood and look at the compressor clutch. If the clutch air air gap is too wide, the clutch will not engage. Checking the voltage at the compressor clutch plug will also tell the story.

[joeb]

if clutch gap is too much, will clutch engage but slip? or not engage at all?

[KHE]

if clutch gap is too much, will clutch engage but slip? or not engage at all?

If the clutch gap is too wide, the clutch won't engage at all. What usually happens is that it wears to a point where the gap is borderline which results in intermittent clutch engagement. It is a simple adjustment to correct but it requires a special tool (clutch plate installer) plus a set of feeler gages.

[Ion]

Note that the A/C fan will continue to run but the air will slowly warm up of the A/C compressor drops out. If the fan is what it cutting out, you may have a bad connection to the fan motor or possibly a fan motor that is going bad. If the fan runs, but the air comes out the footwell instead of the A/C vents it could be the air mix doors. That should throw a code such as

B440 Air Mix Door Problem

A040 Air Mix Valve (Door) Circuit Problem

You can get an idea whether or not the A/C clutch is slipping by parking, letting the car idle, and watching the compressor. When the compressor engages, you will hear a click and the compressor will turn. When it is NOT engaged, the pulley will turn but the compressor will not. If it's slipping badly enough to see, the clutch probably will work OK with an air gap adjustment.

You know that the A/C is running if the fans run at low speed all the time, even when the engine is not hot and the temperature gauge is reading straight up. If you don't hear a click at all, then there is an electrical problem or the clutch is bad.

IIf the PCM is turning off the A/C compressor, the PCM or PZM will set a code such as

B112 A/C Low Side Temperature Circuit Problem [A/C Clutch]

P123 (E123) A/C refrigerant pressure was too low

P126 (E126) A/C high pressure switch disabled A/C compressor

P128 (E128) A/C was disabled because of high refrigerant pressure

the only codes created were related to the MAP sensor issues and resulting engine stalls

[Cadillac Jim]

When you say that the A/C "shuts down," do you mean that it blows warm air, blows through the floor vents instead of the dash vents, or stops blowing at all?

This is very important because it means the difference between looking at the compressor/Freon/condenser/expansion valve, the temperature control doors, or the blower motor.

[Ion]

When you say that the A/C "shuts down," do you mean that it blows warm air, blows through the floor vents instead of the dash vents, or stops blowing at all?

This is very important because it means the difference between looking at the compressor/Freon/condenser/expansion valve, the temperature control doors, or the blower motor.

First, let me state that I replaced the blower motor a couple years ago. To answer your question, when it shuts down, there is no flow at all coming from the vents in front, but on occasion, I swear that it feels like there is cold air coming from underneath. And...the backseat vents still seem to be producing cold airflow. Hope that helps!

[Cadillac Jim]

Yes it sure helps. The rear has its own blower motor. You apparently have a blower motor problem. Reach back between the seats and move the slider switch all the way to put the rear fan on High. Since your main blower motor probably isn't bad, I would start by looking at the connector to the blower motor, and at the resistor that is used for the low fan speed. If you run the temp control down to 60 F, that bypasses the automatic controls and everything goes on High; if that works, it's the resistor - an easy-to-change part.

This also explains why you have no codes. All the codes are for the compressor, Freon level, blocked expansion valve/condenser/evaporator/etc, temperature control doors, and such, but not for the blower fan. The cold air from underneath is the flow from the vent that comes through with the fan off.

[Ion]

I'll try to set it to the lowest possible setting to see if that keeps it going. Where I live in AZ, we need it as cool as possible! STILL in the 100's!

BTW...the connector from the new blower motor was not 100% like the original one, so it might be suspect. I was not able to find an OEM one and had to make the replacement one fit into the opening. Yeah, that was fun! And...the silver metal pipe, about 3/8" diameter, that runs the width of the engine compartment (freon related?), just above the blower motor, has one connector (of two visible) where I had to solder a wire back together, so that might be an issue?

[Cadillac Jim]

I don't know about the details of changing the blower motor. Would someone who has done that himself on a 1993-1995 please chip in?

[Ion]

...Since your main blower motor probably isn't bad, I would start by looking at the connector to the blower motor, and at the resistor that is used for the low fan speed. If you run the temp control down to 60 F, that bypasses the automatic controls and everything goes on High; if that works, it's the resistor - an easy-to-change part.

Well...of the 3 wires that run into the blower connector, one blade had come loose. I plugged it back in and the blower now runs, however, it is still intermittently sutting off and re-starting. No biggie for now, because I still have a rough-running engine that does not throw any codes! I am scheduled to bring it to someone who was referred to help diagnose the problem. Are there any general things to look at to begin diagnosing the source of a rough-running engine?

Thanks for the input on the loose connector wire!

[Cadillac Jim]

The plug wires, the spark plugs, the FPR, a dirty throttle body, vacuum leaks, clogged air cleaner, and coils, in that order. Others will have their inputs too.

Note that anything that causes a miss will eventually throw a code, as will a vacuum leak. A clogged air cleaner can throw the same codes as a vacuum leak.