AboutMp2 Expertise I prefer to answer questions relating to the Miata since this has been my area of specific
expertise since 1991. I can answer questions relating to the other Mazda models however
some limitation of expertise may reduce my accuracy.
Experience Mazda technician since 1987, shop owner and specialty are regarding the Miata since 1991 covering mechanical, electrical, trim and body. Specializing specifically in drivability concerns.GKHS 1985, BVC 1987, MNA 1989, ASE Master Technician Mechanical 1995, ASE Master Body/Paint/Collision 1996
Education/Credentials GKHS 1985, BVC 1987, MNA 1989, ASE Master Technician Mechanical 1995, ASE Master Body/Paint/Collision 1996
Question Last year we converted our 1991 Mazda Miata from R12 to R134. We replaced the compressor and dryer. However, after sitting out in heat and driving around in the city, the car will blow warm air. When I leave for work in the morning (6 am), it will blow cold.
Sometimes, it blows cold in the evening and sometimes, it blows warm in the day!
Should we replace the expansion valve or high pressure switch. Any suggestions would be greatly, greatly appreciated.
Get's rather hot here in Texas!
Thank you!
Answer Yeah I feel ya Louisiana too!
It's either low on charge or the expansion valve has an obstruction issue either corrosion or debris from the compressor.
If it feels like it just can't compete against the challenge of a hot day then the charge may be just low. R134A tends to evaporate through seals and O-rings more readily than the old R12 systems. As they get older O-rings and seals harden and change shape which invites the refrigerant to escape during expansion and contraction, very common. Not unusual and actually recommended to have the system evacuated and recharged every 15 months/15k. It removes moisture and scale and replenished the oil and refrigerant charge keeping everything in good working order and extending service life.
On the flip side, if it blows cold for up to 8-10 minutes or so then goes warm and repeats the cycle every so often then that is a sure sign of a blockage at the expansion valve. In some cases it stays blocked in other cases it blocks up (goes warm) then as the system equalizes the obstruction is freed allowing it to cool yet again until it blocks up once more (the cycle) If it is the expansion valve then replace the dryer again and every O-ring that gets exposed during repair.
The R134 i less efficient that the R12 especially in a converted system. Increased head pressure reduces the efficiency in hotter climates because the condenser is not sufficient in size. We have found adding a third pusher fan to the condenser makes a huge difference on pre '94 models in this ambient hot house we live in. Kits are available here.
