2000 V70 high low side AC pressures after accumulator replacement

[Herb Goltz]

Hello all:

I just replaced the accumulator on my 2000 V70. The old one rusted out and the refrigerant leaked out. I bought a new Rein one, added about 3 oz of PAG oil to the accumulator (equivalent to the 90 cubic cm spec) with a funnel where the compression fitting attaches . I recharged the system. It worked OK for a few minutes, but after a while it stopped blowing cold. A quick inspection showed that the clutch was not engaged (the clutch is already shimmed). I put my cheap gauge on the low pressure side, and saw low side pressures over 100 psi, so I shut it down and left it for an hour or two. The pressure was still over 100 psi, so I looked up static pressures (~78 psi @ 75F) and I removed some refrigerant until the pressure was in the right ballpark statically. The system worked well for a while, but then the low pressure began to climb again, resulting in the system cutting out again.

Has anyone had experience with this? The accumulator replacement and recharge were the only work done recently on the AC-- I did shim the clutch last summer. I know it has a slow leak, as I have to add a can or two every season. Any help would be appreciated!

[Herb Goltz]

After letting the car cool down until the static pressures were around 80 psi, I started the car and turned the AC on max and recirc and full blower and watched the pressures. It cycled quickly, with the pressures dropping to about 25 psi, then climbing until the compressor clutch released at around 75 psi. It took a minute or two, but eventually the peak pressures reached the point that the high pressure switch kicked in and the clutch stayed released.

To me this suggests that the clutch, the low pressure switch and the high pressure switch are working correctly. Any ideas of what to try next?

[abscate]

You cant use static pressures to fill, you need to get enough R134 in to get the compressor running then turn it high, and gauge the low and high pressure inVIDA to evaluate

But

By far the easiest way is to vacuum it out, check for leaks, then fill with 750g refrigerant by weight.

Then you are done

The tiniest bit of refrigerant in the system can give a static’s pressure of 25-100 psi

[Herb Goltz]

Thanks for the quick response! I didn't use the static pressures to fill, but rather to try to understand why I had high low pressure readings. I got a decent fill by jumpering the low pressure switch and adding two cans of 134a I picked up in the US while monitoring the low pressure side with an ambient temperature compensated gauge. At first things looked fine-- the system took in the refrigerant and there was a decent frost on the hard line at the the firewall and significant cooling in the cabin. After running the system for a few minutes the compressor clutch disengaged and the cooling stopped. Unfortunately I don't have VIDA, so I don't know what is going on with the high pressure side, but the low side pressures exceeded 100 psi.

Here in Canada AC work is expensive-- a vacuum and fill once the system is sealed is $200-250 at shops in the Greater Toronto Area-- a fairly significant fraction of the value of this car. r134a requires a license here, so the DIY crowd have to use r12a. I am also pretty sure I have a leak at the evaporator, so I'm not sure a shop would actually fill it.

What are the usual suspects for climbing low side pressures?

[abscate]

Here’s the real deal from guru jimmy in TX. 2011 post!

Your 2000 is a “CCOTS” type AC system, see below

Post by jimmy57 » 18 Jun 2011, 14:44

Pressure readings are not the way to do it on CCOT (cycling clutch orifice tube) systems. You can't just add refrigerant until you get that pressure. Temperature and humidity and engine speed all vary the pressures.
You can evacuate and then charge by weight or you can partial charge or charge from empty by monitoring temperature and low side pressure and cycling interval with the engine at high idle (1250-1500 rpm), fan on next to highest speed and recirc selected, the conditions Volvo and others call for for diagnosing A/C systems on cars and trucks.
The high side will not be nearly that high. The system has a high pressure cut out for compressor at about 430 psi.
High side may go 250-275 on a HOT HOT day for a brief time when interior is HOT or go higher than that if there is an airflow problem for condenser or a blockage like a clogged orifice filter screen.

When the system has run for a few minutes in the conditions above per Volvo methods, the vent temperature should be mid 40's if airflow over condenser is below 90F and high 40's to low 50's if ambient temp is high 90's to low 100's.
The low side will get into upper 20's and when car gets cooler inside it will cycle off compressor at 22-24 psi and then come back on when pressure on low side goes up to 42-45psi. IF you turn fan down one speed and it cycles on for 25-30 seconds on a upper 80's day and then turn it up a fan speed and cycling gets longer on period, maybe 60-70 seconds then charge is prefect. The right charge level will also be noted by distinctly chilly low side line all the way back to compressor.
The high side will be over 200 and after car cools down inside the high pressure will be 150-180 unless the ambient temp is upper 90's low 100's and then the high side may stay close to 200 or a bit higher.
Humidity has a bearing on the pressures too. High humidity makes air have higher specific heat and the system works harder and pressures will be slightly higher and cycling of compressor may be on a longer on interval with vent temps 2-3 degrees higher.
A/C systems using expansion valves (s80,s60, xc90, P2 v70 and xc70, 00-04 s40/v40) regulate the low side and to some degree the high side and charging by pressure monitoring is more reliable.

[Ozark Lee]

I did not read the step where a vacuum was pulled on the system. Air is a non condensable gas and it will cause very high compressor high side pressure. As I understand the high pressure switch system it has a lower high pressure limit to satisfy the ECU that the A/C is operating and has built sufficient to require air flow across the condenser coil. That prompts the ECU to turn on the radiator fan.

There is a second limit that shuts down the compressor in the event of a head pressure that is too high. Non condensables in the system can cause the latter condition.

I think this is equally applicable to the entire p80 line but there may be differences with the '99 -'00 cars. The air conditioner was the one thing I never had to mess with on my '99s other than swapping a high pressure switch that I inadvertently broke with a wrench slip.

...Lee

[Herb Goltz]

You are right, I did not have it vacuumed. I found a shop, had it vacuumed and filled with r134a. Working OK for now!