A/C blow full power 5 seconds then 50 % for 15 seconds

williamvomusa · Post by **williamvomusa** » 16 Aug 2011, 11:36

This cycle keeps on repeating its self. is the coolant low? Also found out there is only the A/C belt on the compressor the it looks like there should also the Altenator belt running over it also. I could not find any belt info on here. Thank you very much you guys know it all.

lindy8_man · Post by **lindy8_man** » 16 Aug 2011, 21:18

Is the fan speed changing? or is the AC pump cycling?

If it is the Pump cycling, then the coolent oil could be low. Very easy to add more. Just pick up a can and a delivery system. They typically fill on the low terminal. If this does not fix it, then check for leaks.

williamvomusa · Post by **williamvomusa** » 16 Aug 2011, 21:55

i added a can it did not take it all we will check the coolant level tomorrow what should the levels be? thank you.

Post by **billofdurham** » 17 Aug 2011, 12:14

The 760T has three belts as shown in the attached:

: 760 belts.jpg (30.31 KiB) Viewed 998 times

Has the AC been converted to R134a or is it still using the original R12? If the latter, you can not use R134a to top up. The 'coolant' level is checked by weight, usually working from a fully evacuated system. Your car would have 1100 grams of R12 when it left the factory. If it has been converted to R134a it would have 900 grams of that gas.

The other way to check is by using high side and low side pressure gauges.

: AC Gauges.jpg (12.21 KiB) Viewed 998 times

Below are normal car AC pressure readings with 134A.

Normal readings on high and low side with AC OFF (static pressure) – Depends on outside temperature, but normally is between 80-105 PSI
Normal low side reading with AC on high speed and MAX & engine at 800-1000 RPM’s – Ranges from 25-35 PSI.
Normal high side reading ranges from 200-350 PSI

Bill.

williamvomusa · Post by **williamvomusa** » 18 Aug 2011, 12:37

Thank you for the info I will rent some gauges and get this thing working this weekend.

lindy8_man · Post by **lindy8_man** » 18 Aug 2011, 14:57

Bill,

What would the ramafications be if the new stuff is added to an existing R12 (assuming there were somre R12 remaining)? Do they play nice together? I seem to recall that they both affect the seals differently... What should he look for if his system was not converted?

It seems odd to me that the low terminal did not draw out all the cooling oil from the can. All the instructions I saw was that the risk there was really due to over charging...

Post by **billofdurham** » 18 Aug 2011, 15:23

Mixing R12 and R134a could result in "complete mechanical failure of the compressor or fire." This is taken from a Volvo Technical Service Bulletin.

As regards the seals R134a uses ester oil which mixes well with mineral oils and does not react with materials in the O-rings. This means that the only seals/O-rings which need to be replaced on conversion are those on joints which have had to be opened.

Bill.

williamvomusa · Post by **williamvomusa** » 19 Aug 2011, 13:53

A friend from church had some gauges he hooked up to the left side connection and read 205 psi at 5pm temperature was around 100 degrees out side. He wanted me to find out if that was to low side or hi side he is a General Motors mechanic and not familiar with the Volvo. I was thinking that the left side was the low side and the black cap or cover on the right side was the high side. He did mention that they are some times hard to find, is there a diagram i can show him please. Thank you again