Looking for A/C Fuse & Relay Box

[imidazol97]

Originally Posted by Luke

It was that very location I initially checked, but sensed I'd have to lift up the carpeting on the passenger's side. Is that box higher up, on the foot rest area, passenger side ??? For it was that fuse, which I felt was the one which would power the relay, since I sensed that the #7E, being a 10 amp unit, was not high enough for a A/C compressor.
In my reading of the actual wiring circuitry, I've come up with the same findings, however, you've clarified doubtful information I had.


I'll also be checking fuse # 7E.

Thank you....

The panel on passenger side requires removing the thin plastic panel under the dash that quiets noise from engine. The panel is up high about 10 inches above the floor on passenger side.

[Luke.]

>imidazol 97< Thank you, though, I'm hoping that I don't have to go their.

[Luke.]

I'll be checking tomorrow afternoon. And, of course, will be reporting back.

[BNaylor]

With a GM Tech II scan tool you can command the comp clutch thru the PCM module but there are manual troubleshootng procedures to use in lieu of to check to see if the A/C Clutch Relay is energizing. Once you find out where the A/C Relay is located you can do the following diagnostics. In most late model Buicks the A/C Clutch Relay is typically located in the underhood fuse compartment.

Does the clutch come on if you jump terminal 30 and 87 of the relay?

Does pin 86 show continuity to ground when the A/C is requested.

The HVAC module sends a signal to the PCM across the Class 2 data line to let the PCM module know the A/C has been requested.

The PCM looks at the A/C pressure sensor reading and then grounds terminal 86 to energize the coil on the relay. If this happens, 12v should be pressent at the compressor.

Here is some info on the pressure sensor:
The A/C pressure sensor is mounted on the discharge line of the A/C compressor hose assembly. The sensor's output to the powertrain control module is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage output.

A/C pressure is constantly monitored in order to allow the A/C clutch to disengage due to aberrant pressures:

If the pressures are above 2968 kPa (430 psi)
If the pressures are below 255 kPa (35 psi)

Here is how the A/C system operates:
The engine belt-drives the compressor for the air conditioning system through the A/C compressor clutch. The clutch allows the compressor to cycle on and off. During most normal operation, the compressor will be in the ON position. The compressor will disengage under the following conditions:

When the air conditioning is OFF
When the engine load must be reduced
When the automatic system requests the system FRONT DEFROST or A/C, the heater and A/C programmer sends a request message for the compressor. The request message travels over class 2 serial data communications to the Powertrain Control Module (PCM).

Under normal operating conditions, the PCM supplies a ground to the A/C compressor control relay coil, and the relay energizes. The A/C CLU fuse and the A/C compressor control relay contacts supply voltage to the A/C compressor clutch. The A/C compressor clutch engages, and the compressor runs.

If the PCM determines that the engine load needs reducing, such as during full throttle conditions, the PCM will de-energize the A/C compressor control relay. De-energizing the relay will disengage the compressor, even though the voltage signal from the heater and A/C programmer is still present.

The A/C compressor clutch diode is connected across the A/C compressor clutch terminals. The A/C compressor clutch diode provides a path for the current that results from the voltage spikes. The collapsing magnetic field of the A/C compressor clutch coil generates the voltage spikes. Voltage spikes occur every time the coil energizes.

[Luke.]

> B Naylor < As my wife has the car this morning, there will be a delay in my follow-up.

[Luke.]

Initial observations: (( And of course, we have to go to a dinner this afternoon )) Upon rechecking, for the third time, but this time, the full fuse panel/box, under the driver's side dash, I find a fuse slot 5D > 25 A, Base A/C. It's missing, as in empty. Hmmmmmmmm. So I took a 25Amp unit from the #2D Spare slot.

As the weather this Christmas day in Los Angeles is warm, I'll see if this "empty" slot has anything to do with the A/C being inopertive. BTW, this is not a situation where this slot is supposed to be vacant. It's supposed to be fused.

This may be a remote find, with no influence on the A/C compressor activation, but it's an observation.

I should note, additionally, in checking the back center of the engine compartment, after cleaning a light dust layer on the back, low and behold, I find a VERY large covering for the Maxifuse/Relay Center.
Ok, I'm not embarrassed. , So I'm not the brightest living cell getting off the turnip truck..

I'll report back in the morning, with the results of the trip to dinner.

Merry Christmas, you all......

[Luke.]

Well, I've taken time out from dinner -- there was no change to the A/C system. It did not work.

Will report back later.

BTW, in using the Diagnostic Scanner, there were no codes....

The next time I test it, I'll try the A/C "Auto & On" button, at the same time; I want to take those steps to see if the system goes into a Diagnostic test.

Until next time.

[Luke.]

In checking the 'Maxifuse / Relay Center' (((> located under hood, and back firewall area, center & left of center cover. <))) the 30 amp fuse was found to be good.

As my wife had to use the car, it will be next weekend, before I'm able to check the car's cabin passenger side's fuse box. The observation of the A/C's clutch engaging requirement, will be checked when my wife come's home, with the car's engine still running.

It should be noted, the only notation on the dealer's work order was
" Air conditioner replacement recommened and declined."

That was it. No notation of effort, or results, from the actual technician. Remarkable.

Reporting, to continue.....

[Luke.]

I've been working from a copy, made available from this site, of a Acrobat Reader for the 1998 Buick LeSabre Limited.

I'm sensing that the wiring may be different, with particular emphasize on the respective fuse boxes, and fuses on my 1997 Buick LeSabre Custom from the 2004 Mitchell Repair Information company's manual titled: 1997 Buick LeSabre Limited A/C-HEATER SYSTEM - AUTOMATIC , which I found here.

May I ask if anyone can direct me to a similar manual, for my
1997 Buick LeSabre Custom ???

Most appreciative

[Luke.]

1997 Buick LeSabre Limited w/grand touring suspension package.


Ok Guys, here is what I check this afternoon (Sunday)

Attempted, but was not successful in, checking the 'relay switch', which is supposed to be in the "MaxiFuse/Relay" section in the back of the engine compartment [ center, center left ] My problem was that the was no sticker on the master cover panel, which should have indicated which of the four relay switches was for the A/C. Of course, as I understand, all four are the same, however, I did not want to switch any of them, for fear of shutting down something critical.

I was able to get under the passenger side's upper leg panelling, to check the fuses there, and the one for the "A/C Programmer" was found and pulled & checked. It was fine. (( I should note, it was not that difficult to access that fuse panel. It just required removing two small supporting 'screws' holding the knee panelling up, while then slipping the back firewall bolt securing supports, and the knee panel just dropped down. ))

Moving along to my running the engine: Ran at operating temperature, with outside temperature being 70 +/-. Here's what I noticed; Upon pushing the "automatice" button, the interior fan came on to it's initial high speed. Outside temperature registered as 73 on the center panel, with my setting the A/C temperature reading to 65.

Interestingly, not only did the compressor not activate [come on, as in the compressor's clutch engaging], but neither of the two fans on the radiator were activated. I noticed no difference in the RPMs, nor here the Relay Switch's magnetic "click".

I also took the steps to turn the HVAC to windshield, thinking that the A/C is also supposed to engage when that request is made. Results, also, the same.....no engagement of the compressor, nor radiator fans coming on.

With these results, my next inquiry will be that of the freon level (or what ever is used in the newer cars---R122 ????). If memory serves me correctly, these, and probably all cars, have a shut off switch, whereby, should the freon exceed, or drop below a given threshold figure, the A/C computer will have received that reading, and not allow the A/C to engage -- thus saving the compressor from damage, due to low, or excessively high freon pressure readings.

Of course, if that is the case, then a "leak" will have to be found.

Reports to follow, with appreciation for any input from you all.

[HotZ28]

Originally Posted by Luke.

With these results, my next inquiry will be that of the freon level (or what ever is used in the newer cars---R122 ????). If memory serves me correctly, these, and probably all cars, have a shut off switch, whereby, should the freon exceed, or drop below a given threshold figure, the A/C computer will have received that reading, and not allow the A/C to engage -- thus saving the compressor from damage, due to low, or excessively high freon pressure readings.

Of course, if that is the case, then a "leak" will have to be found.

Reports to follow, with appreciation for any input from you all.

Originally Posted by buckroo

You may want to check the pressures of the refrigrant. When it gets low the unit will not come on.

Originally Posted by HotZ28

I concur with Buckroo, about the refrigerant being low.

Originally Posted by bnaylor

Here is some info on the pressure sensor:
The A/C pressure sensor is mounted on the discharge line of the A/C compressor hose assembly. The sensor's output to the powertrain control module is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage output.

A/C pressure is constantly monitored in order to allow the A/C clutch to disengage due to aberrant pressures:

If the pressures are above 2968 kPa (430 psi)
If the pressures are below 255 kPa (35 psi)

I would agree, get the Freon level checked!

[Luke.]

Can that Sensor's Output be checked ???? I do have a volt/amp tester.


As a side, info, note; It should be stressed that, upon initial reading about obtaining access to the fuse box on the passenger's side, it was actually rather simple. The paneling which had to be removed, was the panel which sits just above the passenger's knees, and sits just below the glove box door. The actual fuse box, sits on the side wall, to the right of the passenger's right knee. One can actually 'see' the box, when the glove box is opened beyond the rubber stop points.

[BNaylor]

Before you get into that did you consider HotZ28's suggestion about checking the refrigerant charge? You have a low pressure port most likely at the firewall where it can be checked with standard A/C gauges with adapters for R134a systems. Also, there is a high pressure port by the accumulator. The low port is easier to check DIY.

The pressure sensor is both a lo/hi type. The output is not that easy to check since it is supposed to vary based on the refrigerant charge and the electrical connector must be left on. The PCM module provides approximately a 5 volt reference signal to the sensor then the sensor outputs a DC voltage representative of the system pressure. Unlike older A/C systems the sensor cannot be jumped or bypassed. A resistor simulating normal pressure between the low and high threshold voltages must be used.

If charge is good the next easiest step is to bypass the A/C Clutch relay at the normally open or closed contacts to see if the compressor engages.

[Luke.]

Fm B Naylor

..did you consider HotZ28's suggestion about checking the refrigerant charge?

I'm considering that now, however, the two guage set-up I have, I've only used on the old A/C systems, with my never having to do it on a R134a system. I'll look for the 'low port' connection.

If charge is good the next easiest step is to bypass the A/C Clutch relay at the normally open or closed contacts to see if the compressor engages.

My problem with that, is that of the two relays, sitting under the panel of fuses, neither is labeled. Reminder: there are two separate fuse rail/bus, with two relay switches under each fuse rail/bus. I'm assuming that one of the two, sitting below the rail which houses the 30a A/C fuse, is sitting there.

The output is not that easy to check, since it is supposed to vary based on the refrigerant charge.
and the electrical connector must be left on

Thank you for that specific information. Very informative, and of course, helpful.