Truck Air Conditioner - Updated After Repairs

Truck Air Conditioner - Updated After Repairs

What is your output temperature

07 August 2011
06:08 PM
Had the truck in heat this weekend for the first time since I purchased it.  The truck A/C unit worked okay until the temp outside reached about the mid 80s. but could no longer cool the inside of the truck after that.  Didn't have a leak but knew the system was low on Freon. I evacuated the system, vacuumed it down, and recharged it.  With the outside temperature in mid to upper 90s the best I could get out of the A/C system was 50 degrees.  I was expecting this system to produce upper 30 low 40 temperatures to keep the inside of the truck cool.

How is the A/C system on your truck working?  Lots of cold air? Or similar to what I'm getting - 50 degree output?

07 August 2011
06:29 PM
Just recharged mine a few weeks ago.  Cold air comes out at 29-31* and will stay there....
Good luck,
07 August 2011
08:34 PM
Sitting still, you should see a 30 to 40 degree drop from outside temp, if everything is right.  Running down the road with air moving over the condenser you could see 45 degree drop, if you are lucky.  AC systems will make you pull your hair out if they are not right.  If we open up a system we go ahead and replace expansion valve, air dryer and add dye to the system.  Keeping the condenser and radiator free and clear of anything really helps.
07 August 2011
09:19 PM
T\turn the hot water off to the dash heater, see if that helps.
07 August 2011
09:33 PM
We have had to start adding a valve and turning off the hot water to every truck running thru our shop this last month or so.  But it was only 114 out here west of Fort Worth all week.  Add the high temp and low temp and our 24 hour average the last 10 days has been 99.2 degrees
Dennis M
07 August 2011
09:37 PM
Never measured the temp at the vents, but since we eliminated the leaks a couple of years ago it keeps the cab nice and cool even in the high 90's and the temp is very stable.

FYI we eliminated the leaks by removing the sleeper AC and using plumbing for a day cab.

07 August 2011
10:07 PM
I have the climate control system on my truck.  After dumping the system, vacuuming it down, and recharging it cooled the truck down going down the highway and the fan shifted from blowing on high all the time to blowing on
low. Temp was 95+.  Monitoring the output on the vents I was seeing mostly 50 degrees.  Air was on recirculate.  With the truck sitting, fan on medium, outside temp 90, it was blowing 52 degrees.  As mentioned above, with the volume of the cab and sleeper on these trucks and what they're used for, I was expecting to see at least low 40 and possibly high 30 coming from the vents.

The A/C was working fine until I got into the high temps so that told me I didn't have any leaks but the system was low on Freon.  May replace the expansion valve and dryer.  Truck only has 391K miles.

One last question on this.  When charging the system the pressures drop down when the engine fan turns on.  When the fan turns off, even though the compressor is still running, the pressures climb. I set my pressures when the fan was running.

08 August 2011
12:23 AM
Another thing to check, even though you have “recirculate” selected, is the outside vent(s) closing?

For a quickie troubleshoot, take a water hose and spray the condenser coil and see what sort of temp change you get at the outlet vent.  If there is a big change, that would indicate an obstruction or reduction in airflow across the condenser. If there is little or no change, there is either heat coming into the air duct (stuck mix air valve) or a weak compressor OR an obstruction in your refrigerant lines.  It can be worth spending some money to have a reputable A/C shop run a quick check for you.

They should be able to check the system out, including a leak check for under $100.00.

Mark & Dale Bruss
08 August 2011
06:14 AM
When it is hot out, we run the sleeper AC at full and adjust the dash as needed.
08 August 2011
08:46 AM
The dryer is an easy item to change.  How much work to replace the expansion valve?
08 August 2011
12:00 PM
I second the running the sleeper air.  It really helps unless you pull the curtain between.  The Dash air is only for the drivers compartment and not really up to cooling off the Huge sleeper in my 770.
Jack Mayer
08 August 2011
01:45 PM
My truck puts out 34* on the driver vents.
08 August 2011
05:32 PM
Before moving to Alaska, 29-31F when everything was correctly charged, etc.  At 35F vent temps started looking for issues / problems.  A/C problems will cause you to go bald more quickly than normal but these systems are relatively straightforward and there are only a few items that can really go south.  I have been told by numerous techs that the primary source of lost charge is leaking Schrader valves at the pressure tap connections - especially true if the system is over 5 years old.
08 August 2011
09:03 PM

TFS, on 08 August 2011 - 08:46 AM, said:
The dryer is an easy item to change. How much work to replace the expansion valve?

It is not bad.  I think it is on the passenger side dash.  Always replace the 0 rings on everything you take apart.  We put dye in everything we re-charge.  The cheaper we try to fix a system the better chance it will be a "comeback," better to replace the expansion valve and dryer every time for the best cooling.  As I have said better CHECK for a cabin air filter, a dirty filter will drop a system 15 degrees.

08 August 2011
09:24 PM
Thanks for everyone's responses.  All good input.  Little history on this truck so there isn't any speculation.  I purchased the truck in January of this year.  Haven't driven it a lot since then but it has been driven.  Never had any problems with the A/C but then again I've never had it in a HOT climate until this past weekend to really test the A/C.  What I found out is the truck would cool fine until the outside temps started breaking the mid 80s.  It would still blow cool air but not cold enough to cool down the truck.  Based on this and the fact I've owned the truck for seven months now  I don't think it has a leak.  Yet, for who knows why it was low on Freon.

When I evacuated the system and vacuumed it down what struck me as odd is I had the system under about 20 lbs. of vacuum and all of a sudden it jumped to around 10 lbs. of vacuum.  Then, as I continued to draw down the vacuum once I reached the desired 30 lbs. and was getting ready to close the valves all of a sudden it jumped to 20 lbs.  Never seen this before so I don't know if something was going on with the vacuum pump or something was opening up in the system.  Once I reached 30 lbs. of vacuum the second time and shut everything down it held the vacuum without any further issues.

I ordered a new expansion valve and dryer today.  Once I replace these I'll see how much things change.  It'll be a couple more weeks before I can report back as the hitch is being installed.  I changed my two cabin filters right after purchasing the truck.  They were filthy.  I had Class8TruckParts send me the parts listing how I could see where the expansion valve is.  I didn't think about the O-rings and they didn't suggest them.  I'll make sure I get

Jack Mayer
09 August 2011
12:11 PM
I've been told by very experienced HDT AC techs that the most likely place for a leak - other than the Schrader valves - on a Volvo is the line that runs to the rear HVAC from the front.  Mine was leaking down in less than a month (at best). Once that line was replaced (it had rust-induced pinholes all through it) I have had no further issues.
11 August 2011
12:27 AM
I had to have the lines from the front to the rear system replaced also.  I also had the compressor replaced. Good luck.
11 August 2011
07:50 AM
I just had a line replaced last week.  It had rusted through under one of the nuts.  I guess it's a pretty common occurrence
11 November 2006
11:00 PM
Update on this.  Truck has the climate control system as previously stated.  Changed out the expansion valve and the dryer.  In the process I had to remove the entire air control box inside the cab so I have now removed everything attached to the firewall on the inside of the truck except for the steering column.  Some of you may recall the project I undertook where I removed the entire dash to repaint it only to discover all the horse hair inside the dash.  I'm glad I removed the air control box because I found what appeared to be a mat covering the evaporator coils - it was more horse hair.

After replacement of the expansion valve and dryer there was no change on the output of the a/c system.  It would still only put out 51-52 degrees.  Based on the comments above I even clamped off the water line going to the heater (heat exchanger).  No change even with the heat exchanger now cool.

One of the things that confuses me is the association of the A/C compressor to the engine fan.  When the fan turns on the pressures on the A/C system drop down to normal.  When the fan kicks off the pressures climb.  The compressor remains engaged the whole time.

Back to the temp output. I set the sleeper fan on 2 (4 speed settings).  The temp in the cab is set to 70 and the fan and output are set to the auto position.  Traveling through 98 degree temps the truck cools down and the fan cycles down on low while blowing out low 50s on the thermometer.  Not where I want it to be but the cab is comfortable.

Next test.  Outside temp 65 degrees, turn the temp down from 70 to the lowest setting.  Output temp: no change. Will still only blow 51-52 degrees.  Now I'm really confused.  So is there a temperature sensor somewhere that limits how cold the A/C will get on trucks with climate control systems?  And why does the operation of the engine fan change the internal pressures of the A/C system?

06 September 2011
08:57 PM
I can maybe answer one question for you - the reason for the A/C system pressures changing when the truck fan runs is -- as the refrigerant head press/discharge pressure rises there is a pressure switch that will cause the fan to turn on, this will bring the head press down.  As the head press goes up so will the suction press rise, when the fan
runs it will move air across the A/C condenser coil that is mounted in front of the radiator, which will in turn remove more heat from the refrigerant, which will lower the head press and will also lower the suction.  If you are cruising down the road then the condenser is catching the head on air to cool the refrigerant.  When sitting still and
checking the unit you have no wind so the truck fan is having to do the job of removing heat from the refrigerant.

IMHO, if when charging the system the truck fan is running a bunch, and/or cycling on and off a bunch I would be concerned of an over charge of refrigerant or a possible restriction in the refrigerant circuit.

Hope this helps some.

Bill B
06 September 2011
11:17 PM
Probably not what your looking for, but to the right of the cigarette lighter and power plug is a little grill.  Behind that is a thermistor and a little fan.  That measures the inside cab temp and compares it to your setting. (I have the same climate control).  Mine was loaded with dust and cigarette tar.  I cleaned that well, and reinstalled it with new gaskets and mounts and that helped a lot.  If it is blocked or in the dash area instead of sucking cabin air (reference).  You should be able to see it looking down from the lower fuse area to the floor of the passenger area.
Mark & Dale Bruss
06 September 2011
05:53 PM
We had a hot day today in Northern Wisconsin and the A/C wasn't putting out cold air.

Normally I would pop the hood, see a flashing red light on the A/C monitor, put the gauge on the A/C line, find it low (as the flashing red LED would indicate), put some Freon in until the gauge gets into the green zone. and get cold air.

But today, the green LED is flashing, the compressor clutch is engaged, and the Freon gauge is in the green zone and yet I am not getting cold air.

Hope this isn't a big problem