Air Conditioning stops working at idle

[Ookpic]

Hey all

I know I'll likely have to take this in for further testing and pressure reading but wondering if anyone had a similar issue so I have an idea what possibly to expect. I'm definitely not an AC guy but I can troubleshoot electrical gremlins if need be. I've browsed through similar posts but nothing really same as my symptoms as far as I could find.

Symptoms...

AC blows nice cold air when driving in the city or on the highway. Car cools down no problem at all. However, when engine comes to idle at a stop sign or traffic light, almost immediately the cool air stops and just blows outside temp air. I can even detect that transition smell when you turn off your AC normally which makes me believe the compressor is turning off.

Testing...

-- Both cooling fans run at low speed when engine off, ignition on, AC button on and lit.

-- While driving if I depress clutch at highway/city speed and coast in idle, AC stops blowing cold air. I believe this would eliminate anything temperature wise. Especially on the highway. Lots of air flow.

-- While driving at highway/city speed, if I just coast while in gear, AC continues to blow cold air.

-- While driving at highway/city speed, if I coast with clutch in and keep RPM at 2000, AC continues to blow cold air.

Any ideas appreciated.

 

[irvingj]

Yes, you need to have it checked out by an A/C shop ... but it sounds to me like it may be slightly low on refrigerant charge and shutting off on the low pressure switch.

When the compressor slows down (engine idle), the low side pressure drops enough to trip the LP switch and disengage the compressor; when running faster, there's just enough refrigerant in there to raise the low pressure enough to keep it going, and just enough refrigerant to do the job of cooling.

If that's what it's doing, eventually you'll probably experience evaporator icing.

 

[turbocharged798]

There is no low pressure switch on these cars.

You really need to hook up AC gauges to see what is going on. It could be a clogged condenser causing the system to go off on high pressure.

 

[csstevej]

Yes there is .

 

[KLXD]

Seems to me that at idle the low side would go up with less suck from the pump and less cooling from the condenser.

 

[DivineChaos]

If the a/c stobs blowing cold at idle, but is better but not ice cold till many miles on the hwy. I suspect your RCV valve. Common be problem. Not many of these have a clutch anymore. It is possible the pressure is off. But it'll ha e to be refilled after the valve is changed.

 

[burpod]

Maybe check with multimeter to see if the ecu is shutting off the ac. Don't remember which wire off hand, but iirc there is a wire from ecu to ac shutoff relay pin #85 I think. If the ecu is shutting it off that might give another clue

 

[Ookpic]

Yes, you need to have it checked out by an A/C shop ... but it sounds to me like it may be slightly low on refrigerant charge and shutting off on the low pressure switch.

When the compressor slows down (engine idle), the low side pressure drops enough to trip the LP switch and disengage the compressor; when running faster, there's just enough refrigerant in there to raise the low pressure enough to keep it going, and just enough refrigerant to do the job of cooling.

If that's what it's doing, eventually you'll probably experience evaporator icing.

Thanks for the reply!!

I'm thinking this is not the case because if the compressor disengages from a LP switch then, there would be no way to re-engage the compressor as the if it is dis-engaged, it would not be able create more pressure when engine is not at idel to re-engage by itself. UNLESS the compressor is not disengaging at idle.

 

[Ookpic]

Update...

The AC totally stopped working altogether yesterday. I'm checking the pressure on the low side tmo. If nothing is obvious, it's off to an AC specialist for diag. I'll keep this thread alive with results if there is interest.

Thanks for all the replys!

 

[irvingj]

Yes, Ookpik, that's a logical response -- obviously, my AC troubleshooting days are far behind me! What I do remember, however, is that LP switches are self-correcting (no lockout) -- it was just a thought, that maybe the pressure could build back up to a point so it could re-set, maybe just from the heat of the engine.

So far, the AC on my 2005 (160K) is still working well, but let us know what you find out -- I may have to go through this at some point, too.

 

[Ragdude]

My money is on low charge, these newer cars take so little and are very fussy about it. Not like the older cars when ya just put another can in if it wasn't cold enough.

 

[csstevej]

My money is on low charge, these newer cars take so little and are very fussy about it. Not like the older cars when ya just put another can in if it wasn't cold enough.

His car is a 2002……don’t think it’s too new

 

[Bengoshi2000]

Low charge or RCV. I replaced the RCV in mine. Problem solved. Been 40-50k miles since. Assuming it's the RCV it could be a cheaper fix than a new compressor... don't let them sell you a new compressor unnecessarily.

 

[Ookpic]

UPDATE...

I had a friend come over that has a spare gauge from one of those fill yourself kits. It had no can but the object was just to compare pressure on the low side while the car is off and while running. The low pressure side port is always showing high pressure. My rudimentary knowledge tells me that the expansion valve should limit the high pressure flow as well as convert down to low pressure which causes the cold on the low pressure side.

Again if I understand correctly when the car is not calling for AC (or engine is turned off) the high and low side should equalize. Then when the AC is called for the compressor builds pressure and the expansion valve converts to low pressure cold gas just before running through the evaporator for the blower fan to blow that cold goodness into the cabin?

The car is booked into my trusted non-TDI family mechanic for tomorrow as I don't want to start just swapping parts but since I am still reading pressure, it's not likely low on gas. So I'm betting on Expansion valve, receiver/dryer or possibly compressor but it was changed 2 or 3 years ago with a brand new unit so hopefully not that. lol

I'll update tomorrow.

 

[csstevej]

But what was the pressure? That’s why I ask you use a/charges and see what exactly you have both on and both off.
I highly doubt it’s your expansion valve , if the compressor did kick on and low pres was higher than it should have been then I’d suspect that it’s the RCV in the compressor, if it is that you do not need to replace the compressor. It can be taken apart and replaced , can even be done while on the car.
It would have been nice if you posted pressures with the correct gages.

 

[Ookpic]

But what was the pressure? That’s why I ask you use a/charges and see what exactly you have both on and both off.
I highly doubt it’s your expansion valve , if the compressor did kick on and low pres was higher than it should have been then I’d suspect that it’s the RCV in the compressor, if it is that you do not need to replace the compressor. It can be taken apart and replaced , can even be done while on the car.
It would have been nice if you posted pressures with the correct gages.

Yeah, sorry. As I said I only had available to me one of those crappy gauges that come with the fill it yourself cans. It was in the red with both the car running and when it was not running meaning high pressure. I don't have access to any proper gauges that's why I'm taking it into an AC shop tomorrow. I'll leave a nice note about the Refrigerant Control Valve on the compressor. Although, I don't list it in my local dealer parts account. If it is not an easily attainable part, I may have to bite the bullet.

Is this the valve you are talking about??

More Information for UAC EX10067C

If not, do you have a part number? My mechanic is friendly with my bringing quality parts from my euro parts place.

 

[csstevej]

Polarbearinc.com is where I get my stuff and there quality parts.

Most mechanics wont do this or don’t know about it, they just change the compressor and go from there.

Here is a guide on how to do it.

CHANGING THE SANDEN SD7V16 CONTROL VALVE TUTORIAL

and the part.

Sanden SD7V16 compressor control valve.

Automotive AC Sanden SD7V16 variable displacement compressor control valve.

www.polarbearinc.com

 

[Ookpic]

Thanks very much for the info! If they diag it to the compressor I may have them just evac the system and I'll order that exact part from RockAuto. Being in Canada, the one from polarbear may cause shipping issues. I found the exact part on Amazon. UAC branded EX10076. So if that's what they reckon is the issue and they don't want to replace that part, I may order it and give it a shot and have them evac the system while I change the part. Thanks again for the info!

 

[csstevej]

Don’t forget the o-ring and the gasket . You’ll see it in the how to I sent you .

 

[Ookpic]

Don’t forget the o-ring and the gasket . You’ll see it in the how to I sent you .

Yup, already saw that. We'll see what they say at the shop. Just because of time frame and parts coming from Florida, I may just bite the bullet and install new compressor if that is what they diag the problem is and keep the old one and order parts and ship them USPS (2weeks time usually) and replace that valve and gaskets myself and keep as a spare.

This is the problem with ordering from the US for us Canucks. So a simple $30USD part ordered. We pay the massive shipping costs ($90USD to get it here in decent amount of time), then we have to pay brokerage fees to get it across the border quickly. Then we have to pay the exchange rate and then we pay our provincial tax. I roughly calculate that the valve and gasket kit will cost in the neighbourhood of $205CAD NOT including brokerage fees which I have no way of calculating but guaranteed it would be over $50CAD. So conservatively, I'm at $250 for $50 worth of parts. I can get a brand new BEHR compressor with clutch for $390 and it's in stock at my parts supplier in town and can be installed same day.

IF of course that is the problem. lol

 

[Drewser]

For what it's worth, down here AutoZone and O'Reilly loan compressor manifold gauges for free. Don't know if they offer that up there.

 

[Ookpic]

For what it's worth, down here AutoZone and O'Reilly loan compressor manifold gauges for free. Don't know if they offer that up there.

I can purchase a full set of gauges for under $70 here but without the technical AC knowledge, I think it may be a waste of funds. I've approached my hobby mechanic friend to maybe go halfers on a set of gauges for future troubleshooting though. This car is almost half a million kms on it so I just need it to last for a few more years at this point. I keep it well maintained so hoping the AC won't be stupid expensive to fix.

Thanks!!

 

[jimbote]

fyi; if the refrigerant level is low, as in below the threshold for the clutch to engage, then it will never get cold because the system needs to see a bare minimum of pressure first. Also, there is indeed a high/low pressure switch. Too low no workie, too high clutch operation gets interrupted.

 

[Ookpic]

Looks like @csstevej is correct. Pressure is fine, clutch is pulling in but not pumping. I fully suspect it is that compressor control valve inside the compressor and I asked them if they do that type of thing and he said no. If I get him the compressor, I should have the car back today. I'll be keeping the old compressor and ordering the gaskets and valve shipped on the slow boat and I'll repair it myself and keep as a spare. Thanks for the help!!

 

[KLXD]

Common wisdom is the "expansion valve" on the firewall should be changed also. Not too spensive but you don't want the Chinesium knockoffs. Availability may be a problem for you too.

 

[UhOh]

I'll toss in a step to test any new (or just new to the car) compressor to make sure that the coil works. Simple, quick resistance check should show a functional coil to be between 3 and 4 ohms. Nothing else is acceptable as it's usually a sign of a short or an open. Might save someone else from the aggravation that I'm going through.

I recently installed a new compressor (Nissens), along with a bunch of other stuff, and after the system was charged turning it on would result in a blown #16 fuse (fans would run even with key removed from ignition!). Compressor coil was shorted. Checking showed it to be 0.3 ohms. Cheaper for me to buy a replacement coil and install than to evac system and then refill in order to facilitate a replacement of the compressor. Still waiting on time to replace the coil (now that summer is gone)...