mel_t_vin

Is it worth it to have a mobile tech come to a house to ascertain the condition of an HVAC system for $60, $50 of which would be applied to any required repairs?

Why not simply drive to a shop, you may wonder? Well, it's not my car and currently not tagged.

In any case, I suspect putting the system on vacuum is not difficult. And charging the system is probably not difficult, either. But, on the driveway, in the elements, without a lift, wouldn't it be relatively difficult to determine the origin of leaks [even with fluorescent dye] to do a proper/adequate repair, if necessary?

Tsmith84

It depends on the size of the leaks. If it's a very slow leak, any dye could take a day, week or month to show up. Is your car still r12? A proper r134a conversion should not be done in a drive way. There is a lot more to it than just slapping on new fittings and filling it with r134a, but unfortunately that is what usually happens. If your car has already been converted, and he is going to vacuum the system and refill with dye for $60, that's cheap. I would make sure it is quality r134a without leak stopper. Most of the stuff you get in a 12oz can at the parts store is crap. Suva is pure r134a with no additives.

mel_t_vin

This particular car is still on R12.

I'm pretty sure my friend was quoted $60 to diagnose the system. Now, I suspect for $60, that would include a system vacuum and charge...dye may be extra. Will have to remind her to ask the tech about this when she calls them back.

The only downside I see [besides doing this on the driveway, in the elements] is that the mobile tech will only have the system under vacuum for maybe an hour, or so. I guess if it leaks quickly, that would point to a sizeable [easily seen?] leak.

This HVAC system has been inop, and has sat uncharged, for at least 7 years. That said, besides adding some compressor oil, would you replace the drier bottle before [to aid diagnosis], or after [finding no leaks], the testing process?

Tsmith84

Being that the a/c system has been inop for 7 years, I would suggest a flush with new oil and receiver/dryer. First, I would recommend a vac test. Problem with a vac test is that it only shows whether the system is tight or not. Trying to find the leak is typically done with a charge and dye. Now, $60 likely does not include this, as r12 is more than $60 per lb. It stopped being produced years ago and one it's gone, it's gone. Hence the price. In this situation I would go with a r134a conversion after a flush, new receiver/dryer, oil and dye. Replace any easy to get to o-rings. Depending on the type of vehicle it is, you didn't specify, an orfice tube would be a good idea. Some oil shouldn't be just added, as there is no way to tell how much is in the system.

mel_t_vin

Thanks for your insight. Okay, so it should go something like this...

1. vac test [holds vacuum - system may be good, or, does not hold vacuum - system has leak(s)]
2. perform system flush
3. install new drier and charge system with refrigerant/oil/dye
4. look for any leak(s)

Does that about sum it up? BTW, what is used to properly flush a system?

Tsmith84

Auto parts stores carry aerosol cans of a/c system flush. 2 cans should do the trick. They are about 20 ounce cans. Flush both directions. Make sure the oil added is compatible with whatever refrigerant is chosen. Ideally, the compressor would be unbolted and turned upside down while spinning the drive to get all of the old oil out. The compressor should get a certain amount of oil and the drier as well. Then the difference would be added during charging. I prefer to charge the high side with the car off, then after it slows to the point of not taking a charge, start the car with a/c on and finish filling through the low side port. Some vehicles have the low side port right at the compressor, and filling here could cause the compressor to hydro lock. Hopefully the a/c tech knows this.

mel_t_vin

Thanks.