Write-Up: AC Compressor & Clutch Replacement

Jack the R wrote:

Nuh-uh, I'm sure you wished you lived closer so your Riv wouldn't have been rusted out by road salt

Well, That Too.

Do you want me to drive down with everything I can think of for troubleshooting and fixing your problem.?

Would need to be done before the leaves start falling.

Oh Shit, I just had to hire a kid in the neighborhood to start raking the leaves so I can do the last cut on the lawn for the season.

Oh Well. I could always ship everything.

That's quite a drive. I'm thinking this is going to get put off to spring if not longer.

Now that I've got my bad HVAC module replaced, and the temperature readout on the HVAC control cluster isn't blinking, I'm ready to look at the AC again. I turned the temp down to its lowest setting, on the main unit and the passenger door control, and the AC clutch did not engage.

I looked at the relay bypasses on Car Wizard's Amazon Affiliates page - Link

But that's $53 for a set that includes at least three I have no use for.

Does anyone know where I can get the one relay bypass that I need to make the AC clutch engage?

Jack the R wrote:

Now that I've got my bad HVAC module replaced, and the temperature readout on the HVAC control cluster isn't blinking, I'm ready to look at the AC again.  I turned the temp down to its lowest setting, on the main unit and the passenger door control, and the AC clutch did not engage.  

I looked at the relay bypasses on Car Wizard's Amazon Affiliates page - Link

But that's $53 for a set that includes at least three I have no use for.

Does anyone know where I can get the one relay bypass that I need to make the AC clutch engage?

Remind us what you have tried?

On my car, every 3 years or so, since it was about 11 years old, I've had to top off the refrigerant. The symptom is, the clutch won't engage. My understanding is that after a certain age the hoses just won't hold refrigerant well, and although the leakage isn't detectable they will seep. One can replace the hoses and not worry about problems for 10-12 years, or one can top off the system. My hoses are still original.

Using the pressures in the service manual (and buying a better-than-bargain level gauge, or renting a manifold set and vac pump from Autozone), you can check pressures yourself to see if that's the problem. When pressure is too low the cutoff switch will disable the system. That switch looks a little like the oil pressure sender/switch, but is mounted on the AC compressor.

I dumped a bunch of coolant in it, and the clutch didn't engage, but at the time I had the problem with the bad HVAC module that could have kept the AC from kicking in.

Before I buy the AC tools, I want to do as much as possible to rule out the climate control unit. Most likely it isn't the problem, but I want to see if I can get the clutch to engage with a fuse relay first.

Jack the R wrote:

I dumped a bunch of coolant in it, and the clutch didn't engage, but at the time I had the problem with the bad HVAC module that could have kept the AC from kicking in.

Before I buy the AC tools, I want to do as much as possible to rule out the climate control unit.  Most likely it isn't the problem, but I want to see if I can get the clutch to engage with a fuse relay first.  

The small gauge on the AC refill can isn't that expensive.  I got mine from walmart. Something like $25 incl tax. Get the one with numbers on the gauge not just the color code, as the pressure range for the "green" pressure level is not exactly the same as what GM says is the OK range in the manual.

The manifold and vacuum pump, around here, can be borrowed from AutoZone for a 100% refundable deposit. I imagine a handyman-quality vac pump and manifold set over amazon.com would be in the $100 range.

I've got the single gauge that only reads the low side pressure. I've read that the double gauge set is necessary.

Hi Jack, hi Albert,
I agree that low refrigerant will trip the low-pressure switch & prevent clutch engagement.
Jack, what exactly do you mean by the "bad HVAC module replaced". I hate to think of it, but I know that the programmer still has to beg the PCM for compressor-clutch control... Have you tried just good ol' hot-wiring the clutch to make sure it's good?
Best,
Mark

HVAC module is the Blower Control Module.

https://www.rockauto.com/en/catalog/buick,1997,riviera,3.8l+v6+supercharged,1022050,heat+&+air+conditioning,blower+motor+control+module+/+resistor,6557

Eldo wrote:

Hi Jack, hi Albert,
I agree that low refrigerant will trip the low-pressure switch & prevent clutch engagement.
Jack, what exactly do you mean by the "bad HVAC module replaced".  

The modules that move the vent doors. I had to replace a split gear.

Eldo wrote:

I hate to think of it, but I know that the programmer still has to beg the PCM for compressor-clutch control...  Have you tried just good ol' hot-wiring the clutch to make sure it's good?
Best,
Mark

I'm trying to find a relay bypass - Link

so I can force the clutch to engage without messing with the wiring.

I've only been able to find these things sold in a package with a few I don't need.

Ahhhh, so it WAS a bit vague...  I thought it was the programmer, Larry thought it was the blower motor module, and it was actually one of the door-actuator pack motors. 80>

ANYway, a bad or disconnected motor will cause the 100-second blink on the CC head but it shouldn't have any effect on the compressor clutch...  Jack, I was only talking about a quick, crude test.  Can you get the connector behind the radiator hose off & run a couple of jumper wires to power?

I think I'd have to put the car on ramps and remove the plastic shield under the bumper.

Sorry for the delay,
We both have '97 L67's, right? Looking under my hood, coming from underneath would be useless... I'm seeing the clutch connector at the top of the pump, with just various wires & hoses getting in the way.
M

Yeah, mine is also a 97.

I could possibly get my hands on that connector if I took off the SC belt and the radiator hose. Or the wheel and the inner fender liner.

I guess what I really need is a way to test for a signal coming from the climate control unit. I just want to rule that out as a potential source of my problem. The compressor was replaced around 2010 and has barely been used. I can understand a seal drying up and leaking freon, but the clutch should have engaged when I dumped a can of freon in it last year. Unless the malfunctioning HVAC door module was also preventing it from engaging. Maybe I've swapped my problems, i.e., now the HVAC door modules work but the freon level is too low again.

As I said, the blend-air pack motor definitely wouldn't affect the compressor clutch.
However, I just had a DUH! moment: Are we overlooking the cheap/easy tests?

- You haven't mentioned the HVAC Relay Fuse in the IP... have you checked/replaced that? It boggles my mind that the trunk & fuel-door releases get a 40A fuse while the compressor clutch gets only 10A, but that fuse powers both the relay and the clutch.

- If that Omron relay is suspect just buy one on eBay for $10, instead of that switch-kit.

- Actually, before that, have you been to the shop manual? You can test both the signal from the PCM and hot-wire the clutch with probes in that underhood relay center. Page 8A-11-5 shows the pinout of the clutch relay terminals, and the schematic is on 8A-67-0. A good ol' needle-tip test light or DMM connected to the battery-cable post will tell you if C3 goes to ground when the ECC & PCM command it, and you can click the clutch with a jumper wire and/or little nails going from C1 to D3.

The instrument panel relay was good.

Looking under the hood, the relay above the clutch relay looks to be the same part.  I think the top one is the horn.  Pretty easy to swap them around and see if the horn works.

How should I set the multimeter up to test for ground, and what am I looking for?

Making progress - I jumped C1 and D3 and the clutch engaged.  So I put the relay back in, restarted, and the clutch engaged again.  I turned the temp up to 90 and the clutch stayed engaged, which is not what I expected, but if I turn the HVAC system off the clutch disengages.  So . . .

The relays must be good (I swapped them around a couple times, and the horn continued to work).

The AC compressor clutch is good.

The HVAC computer is at least sending an on/off signal.

The AC system must have enough freon in it for the clutch to engage, but I didn't feel any cold air coming out of the system, so at the very least it needs to be recharged.  

I don't know why the clutch remained engaged when the temp was set to 90 degrees, or why it's suddenly working when it wasn't working before.

Might want to look at the relay blade connectors for corrosion.

I would include checking the blend door operation, just because I'd want to go ahead and fix anything else that's wrong rather than having to discover it later.

As for the engage-disengage on the clutch, sounds like the refrigerant level (low side pressure) in the system is hovering right around the cutoff point. Heat from the engine bay will change that a little.

albertj wrote:

I would include checking the blend door operation, just because I'd want to go ahead and fix anything else that's wrong rather than having to discover it later.

Which one of these are you worried about? I just replaced a split gear in #3, so I know that one's good. I think they're all o.k. The temp readout in the control unit isn't flashing.

I am curious about 2, 4, and 5.

All the modules on the passenger side work.  

Is 2 visible without dropping the HVAC box?

They all can be removed and put back without the HVAC box dropping - been there, done that.
But driver side is real PITA

Is this a computer wearing a giant heat sink?

It looks like it has to come out to get to module 2.

I don't think that's worth doing. The temp on the HVAC control unit isn't flashing, and if I hit the recirc button I can hear a module spinning in that area. I'm assuming 2 does recirculation - what else could it do?

Even if 2 were out, would it affect the AC?

I've been through section 1C and section 8C of the FSM. The module on the right appears to be the HVAC programmer, but I haven't found the module with the big heat sink yet. Somebody has to know what it is.