New A/C compressor messing with transmission shifts?

[Javier B]

Hey all.
I've been searching the internets for an answer and have gotten zero useful consensus, so hopefully Explorer experts will be able to clue me in.

I swapped out the A/C compressor a couple of months ago. Since then, I noticed the transmission shifting much harder, particularly around 40-50 mph, getting major thumps and seemingly not sure when to shift. Slowly it dawned on me that this seems to only happen when the A/C is running.

So does this make sense? would the new compressor have changed something in engine vacuum or some sensor that affect shifting?
This did not happen with the old compressor, but perhaps something was messed up in the install or needs adjustment? Any advice on what this could be? I heard it could be a vacuum modulator adjustment, and then also heard that the explorer did not have one of those... so I'm a bit flummoxed.

It's a 95 XLT 4WD and has a recently rebuilt tranny that was working super until the the compressor change. thanks all!

 

[Pete Deering]

Hey all.
I've been searching the internets for an answer and have gotten zero useful consensus, so hopefully Explorer experts will be able to clue me in.

I swapped out the A/C compressor a couple of months ago. Since then, I noticed the transmission shifting much harder, particularly around 40-50 mph, getting major thumps and seemingly not sure when to shift. Slowly it dawned on me that this seems to only happen when the A/C is running.

So does this make sense? would the new compressor have changed something in engine vacuum or some sensor that affect shifting?
This did not happen with the old compressor, but perhaps something was messed up in the install or needs adjustment? Any advice on what this could be? I heard it could be a vacuum modulator adjustment, and then also heard that the explorer did not have one of those... so I'm a bit flummoxed.

It's a 95 XLT 4WD and has a recently rebuilt tranny that was working super until the the compressor change. thanks all!

It just happens to be a coincidence. AC is it own system, driven by a belt on the engine. The transmission is it own system driven by it flex plate on the engine. The ECM provides some outputs too those components. AC system, increase RPM when turn on.
They or you could have disconnect a vacuum line or electrical connector.

 

[Javier B]

It just happens to be a coincidence. AC is it own system, driven by a belt on the engine. The transmission is it own system driven by it flex plate on the engine. The ECM provides some outputs too those components. AC system, increase RPM when turn on.
They or you could have disconnect a vacuum line or electrical connector.

Hmm... I have tried this several times with the same results, so I don't think it's a coincidence. Shifts are smooth with A/C off, and hard/bucking when A/C is on. Of course they are different systems, but since A/C changes the load on the engine and the vacuum, it seems to be having an effect on the timing of the transmission shifts, whether because of the ECM or vacuum or sensor or something.

 

[Turdle]

You might check your throttle position sensor.

It's position would be different while running ac, and, it's output voltage controls upshift , downshift.

Have you disconnected the battery to reset the pcm?

 

[Javier B]

You might check your throttle position sensor.

It's position would be different while running ac, and, it's output voltage controls upshift , downshift.

Have you disconnected the battery to reset the pcm?

Thanks! I'll try a PCM reset first. TPS makes sense, but would it only have issues when A/C is on?

 

[Turdle]

Thanks! I'll try a PCM reset first. TPS makes sense, but would it only have issues when A/C is on?

Because with ac on, you need more throttle to achieve the same result as ac off.

Just something to check.

I've had a failed tps which did not allow upshift. Throwing it out.

 

[Turdle]

@410Fortune . Does 95 use a vacuum modulator?

Low modulator vacuum symptom = bad tps symptom by causing late hard shifts.

 

[410Fortune]

No it should be 4r55e not a4ld no vacuum regulator on computer controlled 4r

 

[Javier B]

@410Fortune . Does 95 use a vacuum modulator?

Low modulator vacuum symptom = bad tps symptom by causing late hard shifts.

How/where do I check if the 95 XLT has a vac modulator or if it's all electronically controlled? I have heard both things. they sell replacement vac modulators, but some people insist that the 95 and up models don't have them, so how can I know in a relatively easy way?

 

[Turdle]

OP question
How far does the serpentine belt tensioner arm my ve when ac cycles on ?

 

[Turdle]

Um, wow.
If you need to be sure, you'll have to go see for yourself. Like anything else. Do you see one on the side of your transmission?

 

[Javier B]

How/where do I check if the 95 XLT has a vac modulator or if it's all electronically controlled? I have heard both things. they sell replacement vac modulators, but some people insist that the 95 and up models don't have them, so how can I know in a relatively easy way?

From what I have been finding out, the last explorer tranny to use a vac modulator was the 1994, and so in theory this 95 is electronic controlled. So it's likely a sensor or some bad vacuum elsewhere when the A/C is on. :-(

 

[Javier B]

Thanks! I'll try a PCM reset first. TPS makes sense, but would it only have issues when A/C is on?

HEY. I think doing the full disconnect and power drain to reset the PCM seems to have done the trick! Immediately afterwards it seemed to be better and no bucking or hard shifts since! Didn't think it would would be just that, but it seems to have done it! Thanks for the suggestion!

 

[Javier B]

UPDATE: So following a suggestion, the first thing I did was a PCM reset to make the car forget any prior shifting settings. Disconnected the positive terminal (and connected the power to ground, not sure that actually makes a difference but I've been taught to do that to fully drain the electronics) and after about an hour I hooked it all up again and drove slowly around for a while. After a few miles I turned on the A/C and drove some more and voila, the problem has gone away. Easiest repair I've ever done. Hope it sticks! Thanks everybody for the suggestions.

 

[C420sailor]

Sometimes, a reset does the trick. Sometimes, it does the trick until a certain number of drive cycles, before the problem shows up again. Hope it’s the former!