Help with Volvo VNL780 A/C

Most likely its low on 134 need to book some gauges up to check the pressure if you are real tight with money you can go to autozone and pic up a can that comes with a gauge and start there

 

Yes the pressure switch sends power to energize the relay for the compressor. It's a safety feature to keep from burning the expensive compressor up due to low freon.

To double check, look by the dryer and you'll see the pressure switch with a two wire plug in. Run a jumper across it and see if the compressor comes on.

Then you need to find the leak or a charge will leak back down. Usually it's an o-ring at one of the line connections.

It's much easier and better to get it serviced by someone that has the right equipment.

 

1st did the a/c work when you got the truck...?

when you hit the a/c switch to turn on the a/c does the a/c lite come on....?

if no it's a fuse or a/c switch if yes then it's low or it's OVERDHARGED

some people think it's low so they just add more but if it has to much it woun't work HIGH PRESSURE SWITCH.

 

Do it yourself, if you can put air in your tires you can add freon. For about $40, it is NOT a big deal if all that's wrong is its a little low.

Do a youtube search freon R134a, there are a hundred video on there to show you how.

or click the link below.

[ame="http://www.youtube.com/watch?v=-p2WzuoSHHA"]http://www.youtube.com/watch?v=-p2WzuoSHHA[/ame]

A few tips to remember:

More is not better, don't overcharge.

Hold the can upright. Only flip the can upside down for a second or two if it stops taking the freon. You can actually damage your compressor if you hold it upside down for too long.

Use low side of system. If you buy a r134a recharge kit, the tool it comes with should only fit on the low side.

Add freon only with truck running, and AC set to Max and blower fan on high setting.

If can freezes in your hand, you may need to set it in a bowl of hot water (while still connected to your truck) to help raise the pressure in can back up so it will continue to be drawn into your system.

Have patience, it takes time to be drawn in. Sometimes up to ten minutes or a little longer. Keep shaking the can, it will be drawn in eventually.

If you purchased the tool/kit in that video, you can reuse the tool again and again. Dont throw it away, you can use it on your car too.

 

i've had to add to mine the low psi side is the line at the back below the windshield center

 

In addition to the above, I can add the following:

If you are wondering where the low side port of the AC is on a 2007 Volvo VNL 780, it sits on the firewall, right above the tappet cover, just left of the wiper motor. The port next to the radiator is the high side.

If you are using a small disposable recharge canister with R134a coolant and the seal is punctured by a using the pin screw, unscrew the pin (the pin only, do not unscrew the connector between the can and the hose or you'll end up with a big mess) again after puncturing the seal. If you don't, the pin itself will be sealing the canister and the recharge will not start.

After a while the system stopped taking in coolant. I noticed the condenser (mounted before the radiator) was getting real hot. I unplugged the fan solenoid valve on the firewall causing the fan to come on. In about a minute the condenser was close to ambient temperature (except of course the tubing coming from the compressor, which was very hot) and the system started taking the remainder of the coolant. I have no idea whether it actually makes any difference to the intake rate, it was just one more thing I messed with to try to make it work.

When I started to troubleshoot the AC system, the AC compressor clutch would not engage. What I learned here was that the pressure switch could prevent it from engaging. So I used a separate positive and negative line from the battery to engage the clutch, while monitoring the other end of the plug with a test light. As soon as I engaged the clutch, the test light came on, I reconnected the clutch line and it engaged correctly. Problem solved.

Other links posted by Kansas is useful.