Automotive Air Conditioning Information Forum

1. What should my gauges read with 85-90 degree temp and 90% humidity; Low and High side?
2. Should the engine be running at a certain rpm when you charge the system?
3. If you charge a car at say 1500 rpm at the correct pressure of say 40 psi then your car at idle the pressure shows like 60; is that normal for the pressure to rise

Like I mentioned; I'm a beginner in the ac field but wanting to learn about it. I'm mechanically inclined so I can pick things up fairly well. Thanks in advance to any and all that may respond.

As a beginner you should learn right away that in mobile a/c you need to charge by weight-- pressures mean very little- too many variables. Extract, recover, weigh refrigerant, then vacuum and charge by under hood specified amount of refrigerant. then look at the pressures to notice any pressure deviations..

The system has already been vacumned down so I wouldn't know how was weight came out of it and I was wondering about charging the system back up is the reason for the different questions I asked. Gauge readings; rpm; etc. Thanks

Charge by weight as suggested.

Let me go at it a different way: Say for instance;
1. You put your gauges on a vehicle; what should the readings be in 85-90 degree with 90% humidity if the system is OK.
2. Do you read the gauges at a certain rpm?
3. If the system is low and you add freon; do you install it at a certain rpm?
4. If you add freon at say 1500 rpm to get a reading of 45-55 psi on a R134a system; And when it goes back to idle of 6-800 rpm's is it normal for the gauges to read at a higher pressure?
Thanks to all that will respond. Just trying to learn some on mobile ac.

Gauges are to know if the system is working with a complete charge. Gauges/pressures are not IMO to be used to charge a system. Know the weight for a vehicle. Reclaim any refrigerant that may be in the system and then charge back to the OEM spec.

Mastercool used to have a book explaining the steps. Tim at AC Kits sold them. i have not seen them in a while so I do not know if they are still available.

Dougflas wrote:Mastercool used to have a book explaining the steps. Tim at AC Kits sold them. i have not seen them in a while so I do not know if they are still available.

They stopped making them. MACS has one similar.

http://www.macsw.org/imis15/MACS/ItemDe ... ode=4428-0

goosemaster wrote:Let me go at it a different way: Say for instance;
1. You put your gauges on a vehicle; what should the readings be in 85-90 degree with 90% humidity if the system is OK.
2. Do you read the gauges at a certain rpm?
3. If the system is low and you add freon; do you install it at a certain rpm?
4. If you add freon at say 1500 rpm to get a reading of 45-55 psi on a R134a system; And when it goes back to idle of 6-800 rpm's is it normal for the gauges to read at a higher pressure?
Thanks to all that will respond. Just trying to learn some on mobile ac.

Those questions really aren't valid though - the answers will mean nothing as what you are looking at really tells you nothing about the overall charge in the system. Sorry if we aren't giving answers that you are expecting.

It just seems like the answers I getting is; if you're ac is not blowing as cold as it used to and you'd like for it to be cooler the answers I'm getting is drain the system; weigh what was in it; put correct amount to specs back in. Seems like an AWFUL expense to bear if it just needs a little freon added!!!!!!!!!