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A/C causes push-pull sensation at freeway speed by Rsvl-Rider
Started on: 08-31-2021 01:36 AM
Replies: 7 (184 views)
Last post by: Rodrv6 on 09-13-2021 07:17 PM
Rsvl-Rider
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Report this Post08-31-2021 01:36 AM Click Here to See the Profile for Rsvl-RiderSend a Private Message to Rsvl-RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have an 88 GT with a 3.4 auto and an R134 conversion. It was my daily driver but the car sat for a couple of years until I finally pulled the cracked header and had it welded. I had the car smogged a couple of weeks ago and have been daily driving it back and forth to work. It's only a couple of residential miles each way. I had not had it on the freeway until today.

It's been very hot here. Over 100*almost every day for a couple of months. I recharged the AC around the time I had the smog check and it seems to be working fine on my short daily commute.

Today I took it out for a little joy ride and noticed an odd behavior when the A/C is on. I drove it about 20 miles on some 30 -50 mph twisties with no problem. It wasn't until I got on the freeway that I noticed a kind of pause and surge at about 60 mph and above. Not a stumble really, just a kind of repetitive push and pull sensation that went away when I turned off the A/C. I tried both the Hi and normal positions with the same result. When I turned it off the problem went away. Has anyone had a similar problem? Is it a problem with the A/C compressor, the clutch or...?
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fierofool
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Report this Post08-31-2021 09:23 AM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
There is a HP drawdown any time the ac clutch engages. I think someone had estimated about 5 HP on the Fiero. There's also an extra load placed on the charging system with the ac clutch engaged and the radiator cooling fan running, and the alternator can add additional drag. Do you have a new battery or is it an old one? Watch your volt meter when this is happening.
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theogre
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Report this Post08-31-2021 10:12 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, AC eat some HP outright and the Power needed also eats some more HP as everything loads the alternator. More so w/ SI Alt use on most Fiero but 88 use CS130 > 90 amps peak power as OE.

If have wiring problems anywhere then can have this problem and Volt meter on dash likely anything but stable.
AC compressor w/ problems can cause more load then normal.
Alternator iffy or replace w/ smaller unit can cause this.
People w/ "Power Pulleys" that alone can cause this and other problems.

Before pulling/replacing parts... Start w/ clean/fix all grounds in engine bay, battery cables and + "box" under C500.
Coat ends bolted/screwed to engine etc w/ silicone or brake grease.
This often will help many problems not just this.
See my Cave, Wire Service and rest of section.

Also pull AC/Heat Blower Resistor and Motor and look at them and inside the box...
⚠️ Warning: These Resistors w/ crap buildup can burn a car down.
https://www.fiero.nl/forum/Forum2/HTML/141959.html
Search for more.

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Raydar
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Report this Post09-04-2021 04:22 PM Click Here to See the Profile for RaydarClick Here to Email RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
I can feel this a bit in my 4.9 car.
You might put some gauges on it and check the high side pressure. If it's excessive, it might be putting more than a normal load on the engine.
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skywurz
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Report this Post09-04-2021 09:51 PM Click Here to See the Profile for skywurzClick Here to visit skywurz's HomePageSend a Private Message to skywurzEdit/Delete MessageReply w/QuoteDirect Link to This Post
I bet its a bit low and the AC is cycling off then back on.... Or it could be too high and cycling off due to high pressure as Radar suggests. I have only had the high situation un heavy acceleration. Best to throw some gauges on it.
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Dennis LaGrua
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Report this Post09-08-2021 09:52 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
If the battery is weak then the current surge /load when the AC Clutch is energized may create the push pull situation that you describe . An overcharged A/C system can also do this by placing a large load on the engine when the compressor kicks in. .

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edfiero
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Report this Post09-13-2021 08:01 AM Click Here to See the Profile for edfieroClick Here to Email edfieroSend a Private Message to edfieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
I noticed this issue on my Duke after the 134A conversion every time the compressor kicks in. Seems like the 134a was requiring more HP to run the compressor.

The problem is less noticeable now after my engine swap, but it is still there. I've had the conversion for at least 5 years now, nice cold air, and no problems other than the slight drag when the compressor kicks in.

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Rodrv6
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Report this Post09-13-2021 07:17 PM Click Here to See the Profile for Rodrv6Click Here to Email Rodrv6Send a Private Message to Rodrv6Edit/Delete MessageReply w/QuoteDirect Link to This Post
Bear in mind that these are "Cycling Clutch" air conditioning systems, it's normal for the compressor clutch to cycle during operation. This is how GM prevents evaporator freeze up on these cars. Pretty typical for 80's era GM.

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1988 Fiero GT
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