A/C stops cooling when towing

[PsRumors]

A friend of mine has a 99 SD. The A/C works great until he tows his 5th wheel camper, about 7k lbs. It only takes about 15 minutes of towing and then the A/C blows hot. We have taken a 2 hour trip empty and the A/C works flawlessly.

An A/C shop checked the system out and said everything was functioning correctly.


Any ideas?

 

[POWER-STRUCK]

a/c is designed to kick out when running at wide open throttle. also have you checked the high side pressure? and checked the clutch gap with feeler gauges?

 

[PsRumors]

Have not checked the clutch gap, the shop he stopped at said the pressures were correct but he didn't get the numbers. I'll check it when he gets back to town.

 

[Lethalthreat7.3]

Clutch gap isn't the issue or the a.c wouldn't work unloaded. Definitely check pressures. It sounds as though you may have an issue rejecting the heat from the condenser. What is the truck's engine coolant temp, does it increase quite a bit?
Make sure there aren't a lot of bugs, debris or bent fins.
Are you sure the blend door actuator is working properly. It sits behind the glovebox. If it doesn't close you aren't drawing completely through the evaporator.

 

[PsRumors]

Clutch gap isn't the issue or the a.c wouldn't work unloaded. Definitely check pressures. It sounds as though you may have an issue rejecting the heat from the condenser. What is the truck's engine coolant temp, does it increase quite a bit?
Make sure there aren't a lot of bugs, debris or bent fins.
Are you sure the blend door actuator is working properly. It sits behind the glovebox. If it doesn't close you aren't drawing completely through the evaporator.

Will check all this when he gets it to me...thanks

 

[POWER-STRUCK]

clutch gap could very well cause this problem if the clearances were marginal on the high side of spec and the increased heat from towing could cause it expand thermally and grow past the maximum specification for the coil to engage it. this is a common problem that i have been seeing since these trucks are getting higher miles. if the gap is marginal then just remove a shim, its a free mod why not look into it?

 

[JLDickmon]

I'd look more at the operation of the high pressure transducer and/or the state of charge..
with the increased heat load due to towing, it may be running up the high side pressure to the point it shuts the system down..

OR

it's juuuuuuuuuuuuust low enough on charge the increased heat load on the system boils the refrigerant in the condensor, before it ever gets to the orfice tube..

either way, hanging a manifold gauge set on it is the place to start

 

[Arisley]

clutch gap could very well cause this problem if the clearances were marginal on the high side of spec and the increased heat from towing could cause it expand thermally and grow past the maximum specification for the coil to engage it. this is a common problem that i have been seeing since these trucks are getting higher miles. if the gap is marginal then just remove a shim, its a free mod why not look into it?

I have seen this issue exactly on three trucks in the last year. Removing a shim works perfectly.

 

[Bustedknuckles]

I have seen this issue exactly on three trucks in the last year. Removing a shim works perfectly.

Ive seen it too and that fixed it in my case as well.

 

[e.nickkk]

is the fan clutch working I had my go out and did the same thing but only under load

 

[Big Angry Hillbilly]

is the fan clutch working I had my go out and did the same thing but only under load

This.

 

[Jake]

Fan clutch, slightly low charge does it too at least in my 00