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Ac compressor fast cycling

CrashedGolf

Active member
Joined
May 5, 2018
Location
Georgia Usa
TDI
Mk4 golf 5 speed
Hello, I have searched the forum with no success on the issue. I apologize if this specific issue has been covered. I have a 2001 tdi golf in which the ac has worked great for a long time. My fans quit, I replaced them, they worked, ac still worked. Fast forward 6 months. Now when the car is running and you activate the “ac” button, the ac compressor will engage for approximately half a second and disengage for roughly a second. It will fast cycle about 6 times and will not try to engage again until the car is shut down and restarted. Then the same. I then noticed the fans aren’t running. I replaced the fan control module with a brand new made in Hungary unit. Nothing changed. No fans. Same fast cycling. I have a 2001 tdi Jetta, ac works well in it. With the car shut off it has the same pressure as the golf (high and low side equalized) which tells me it has at least very close to the correct amount of refrigerant in the system. High side gauge barely increases when the pump cycles and the low side barely drops so it shouldn’t be an under/over pressure situation right? I am a couple sweaty days away from relays and toggle switches for fans and compressor. But I hate to void oem function. Thank you in advance.
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
Sounds like low charge to me. When the pump starts the high side doesn't get high enough and shuts it off. Or maybe the low side gets to low. I don't remember where the pressure switches are.

The fact that the pressures are the same in both cars when the systems are off is meaningless. It simply means that there is some liquid in the malfuncfuncfunctioning system, not how much.

A can of refrigerant will be at the same pressure when it's full or only has a drop left.

Oh, how about using more than one paragraph?
 

PakProtector

Veteran Member
Joined
Jan 5, 2014
Location
AnnArbor, MI
TDI
Mk.4 and the Cummins-es
With KLXD on this; sounds like low Freon charge. It is relatively easy to drop some in, and see what happens then. Only add a bit at a time. IF it is low, you'll see the return lines get cold as the compressor drives the charge through the evaporator( and see the compressor run longer ).

Can't resolve the fans not running for you; I thought that the fans would run even if the compressor was not engaging itself.
cheers,
Douglas
 

CrashedGolf

Active member
Joined
May 5, 2018
Location
Georgia Usa
TDI
Mk4 golf 5 speed
KLXD, PakProtector, thank you for the prompt replies.

I can do more paragraphs, maybe not correctly but I can try! Haha

I’m not sure what I was thinking by comparing the “at rest” pressures. You are absolutely right. Had my head screwed on wrong I guess.

It could have 100psi and like you said only one drop of liquid. And maybe my manifold gauge just can’t read the drop in pressure fast enough so show it actually getting super low due to the long hose and whatnot.

I believe I have a can of r134a and I will try putting some in tomorrow for sure. I will feel pretty dumb but also relieved. The lack of defrosting capability has been a real issue leaving work on 2nd shift. (Leaky heater core bypassed, I refuse to pull a dash ever again, I will pay to have it done when I can afford it)

So with no hot and no cold, the windshield does what it wants.

As far as the fans go, I must shamefully admit I haven’t tested with direct 12v power to the plug. I was hesitant without knowing what pin is what. I will search for that data and test tomorrow.

If I get up early enough ?
 

CrashedGolf

Active member
Joined
May 5, 2018
Location
Georgia Usa
TDI
Mk4 golf 5 speed
BobnOH, thanks for the link I will check it out.

KLXD, PakProtector, so I attempted to add r134a today and it did the fast cycle trying to pull more into the system.

After it gave up, I shut the car down, fired it back up and the compressor wouldn’t come on at all. Maybe it’s over full?

I didn’t try letting any out to see if that helped. Maybe it’s completely full of liquid?

I am considering emptying the system, adding as close to the correct amount as possible by purchasing specific sized cans of 134a, then hot wiring the compressor to verify / dial in charge amount based on high and low gauges, then reconnect compressor to wiring harness and see what happens.

Good idea? Bad idea? Please advise. Thank you in advance for input
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
I take it you weren't using high and low gauges? Bad idea to mess with this without them. Not the best idea to try charging even with them and not by weight though I and others have gotten away with doing it.

Hard to tell what's going on. If it was low and didn't, at some point while you were feeding in the gas, start running properly I would say it isn't overcharged.

What I have done on an evacuated system is to attach a full can and fill the system though the high side using a hot water bath to get as much out as possible. Switch to the low side and start it up to pull as much as possible out of the can. This gets an empty can with 30 psi or so worth of gas without worrying about getting liquid into the low side.

Then I switch to a new can on a scale and feed in the proper weight. Not perfect but I figger it's close enough.

Or is it two cans plus part of a third? More or less the same process on the second if it takes three.

Next time I'll keep the first can on the scale and note the weight when the system pressure gets to ambient. This will give a number for how much gas is still in a system that leaks down to atmospheric for future reference.

Call me a hack but it works for me.
 

CrashedGolf

Active member
Joined
May 5, 2018
Location
Georgia Usa
TDI
Mk4 golf 5 speed
No I was using a high / low manifold gauge set from amazon. I used it to when I replaced compressor and dryer on my Jetta and it works great. So I’m inclined to think they work good enough. And with the short period of time that the compressor is running they hardly read different pressures from each other.

I still haven’t tested fans or bled and re charged. Iv been working overtime and thankful for it. I will get to it this week I’m sure. And I will give an update ASAP

as far as calling you a hack, I fixed a hole in a lawnmower deck with gorilla tape this summer and have no grounds for hack calling ?
 
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